Pattern recognition protein binds to lipopolysaccharide and β-1,3-glucan and activates shrimp prophenoloxidase system

Nanoplastic exposure weakens immunocompetence in the burrowing tarantula (Chilobrachys guangxiensis) following pathogen-associated molecular pattern challenges

Nanoplastics (NPs) have emerged as critical environmental contaminants, with growing concerns regarding their potential harm to organisms. Despite this, knowledge remains limited on whether NP exposure diminishes the capacity of organisms to respond to additional environmental stressors. In this study, we evaluated immune function in a burrowing tarantula, Chilobrachys guangxiensis, following NP exposure and subsequent challenges with lipopolysaccharide (LPS) and β-1,3-glucan. The total hemocyte count (THC) and hemolymph encapsulation rate were assessed to determine immune disruption. In addition, transcriptomic analyses were conducted to elucidate the mechanisms involved after both primary and secondary exposures. Results indicated that prolonged NP exposure did not cause significant changes in immunocompetence in C. guangxiensis. However, upon secondary exposure to LPS or β-1,3-glucan, individuals pre-exposed to NPs displayed significant changes in THC and impaired encapsulation capacity. Gene expression profiling based on quantitative real-time PCR revealed that LPS and β-1,3-glucan elicited varying immune responses and distinct gene expression profiles in NP-exposed C. guangxiensis. These findings suggest that NP exposure weakens immunocompetence in C. guangxiensis. This study provides comprehensive insights into the immune responses triggered by different pathogen-associated molecular patterns in NP-exposed C. guangxiensis, offering a novel perspective on the complex immunotoxicological effects of NP pollution.

A C-type lectin of Helicoverpa armigera maintains the stability of the hemolymph microbiota by regulating the expression of lysozyme

An increasing body of evidence suggests that the insect hemolymph is not a sterile environment and that various nonpathogenic microorganisms can stably or transiently inhabit the hemolymph in many insect species. However, little is currently known about how the insect immune system maintains microbial homeostasis within the hemolymph. In this study, a C-type lectin of Helicoverpa armigera (HaCTL6) was shown to be involved in maintaining the stability of the hemolymph microbiota. The expression of H. armigera antimicrobial peptide (AMP) genes was down-regulated after RNAi of HaCTL6. Moreover, the knockdown of HaCTL6 resulted in a decrease in the antibacterial activity and an increase in the total bacterial load of the hemolymph. Transcriptome analysis showed that a lysozyme (HaLysozyme-like) was significantly down-regulated after HaCTL6 RNAi. Moreover, the knockdown of HaLysozyme-like led to a decrease in the antibacterial activity and an increase in the total bacterial load of the hemolymph. Furthermore, the injection of recombinant HaLysozyme-like into the hemocoel caused a significant reduction in the total number of bacteria in the hemolymph. These results indicate that HaCTL6 may regulate the homeostasis of bacteria in the hemolymph by utilizing HaLysozyme-like as an effector.

Characterization of a serine protease homolog from Macrobrachium nipponense and its involvement in AMP synthesis and proPO activation

Serine protease homolog (SPH) with a clip domain is crucial for activating prophenoloxidase. In this study, we isolated and characterized an SPH gene from Macrobrachium nipponense, designated as MnSPH. The full-length cDNA sequence of MnSPH was 1709 bp, including an open reading frame of 1383 bp that encoded 460 amino acids. The predicted MnSPH protein contained a signal peptide, two low-density complex regions, and a Tryp_SPc domain. Although SMART was unable to predict a clip domain in MnSPH, it does possess a conserved cysteine pattern that resembles the characteristic pattern of clip domains. Phylogenetic analysis revealed that MnSPH first clustered with SPH of Pacifastacus leniusculus and subsequently formed a clade with other SPHs or prophenoloxidase-activating factors (PPAFs) from crustaceans. MnSPH exhibited high expression levels in the gills and stomach of M. nipponense, with relatively lower expression in other tissues. Upon infection with Vibrio parahaemolyticus and Staphylococcus aureus, the expression levels of MnSPH were significantly upregulated at multiple time points in the hemocytes of M. nipponense. Furthermore, the knockdown of MnSPH in the hemocytes resulted in the inhibition of several antimicrobial peptide (AMP) genes and a significant reduction in phenoloxidase activity. The survival rate of prawns was reduced after MnSPH knockdown. These findings suggested that MnSPH plays a pivotal role in the innate immune response of M. nipponense during pathogen infection.

Differentially Expressed Genes and Alternative Splicing Analysis Revealed the Difference in Virulence to American Eels (Anguilla rostrata) Infected by Edwardsiella anguillarum and Aeromonas hydrophila

Edwardsiella anguillarum and Aeromonas hydrophila are two common bacterial pathogens affecting cultivated eels, and the differences in their virulence remain unclear. In this study, after two groups of American eels (Anguilla rostrata) were administered the LD50 dose of E. anguillarum and A. hydrophila, respectively, the histopathology of the liver, trunk kidney, and spleen, as well as transcriptomic RNA sequencing (RNA-seq) analysis of the spleen, was examined at three time points: pre-infection (Con group) and post-infection at 36 h (Ea_36 group, Ah_36 group) and 60 h (Ea_60 group, Ah_60 group). The results showed that the differences in pathological changes were characterized by severe hepatocyte edema at 36 h post-infection (hpi) and hepatocyte atrophy at 60 hpi in the livers of eels infected by A. hydrophila, in contrast to the severe atrophy of glomeruli in the trunk kidneys and numerous bacterial nodules in the spleens of eels infected by E. anguillarum. The RNA-seq results revealed 906 and 77 typical differentially expressed genes (DEGs) in eels infected with E. anguillarum and A. hydrophila, respectively, compared to the control eels. The DEGs between the infected and control groups were predominantly annotated in GO terms related to binding, catalytic activity, membrane part, cell part, and cellular process, as well as in KEGG pathways associated with human diseases and organismal systems. The GO enrichment analysis showed 83 and 146 differential GO terms, along with 32 and 78 differential KEGG pathways in two comparisons of Ea_36 vs Con versus Ah_36 vs Con and Ea_60 vs Con versus Ah_60 vs Con, respectively. Furthermore, the analysis of differential alternative splicing genes (DASs) showed 1244 and 1341 DASs out of 12,907 and 12,833 AS genes, respectively, in the comparisons of Ea_36 vs Ah_36 and Ea_60 vs Ah_60. These DASs were enriched in two common KEGG pathways: "NOD-like receptor signaling pathway" and "necroptosis" which shared 11 hub DASs. Finally, analysis of protein-protein interactions revealed that 91 of 412 cross DASs between Ea_36 vs Ah_36 and Ea_60 vs Ah_60 potentially play an essential role in the difference in virulence of E. anguillarum and A. hydrophila in American eels, with 12 encoded proteins being particularly notable. Together, this study is the first to report a comparative pathogenicity and RNA-seq analysis of E. anguillarum and A. hydrophila in American eels, shedding new light on our understanding of the differences in virulence as revealed by pathological changes, DEGs, and DASs, contributing to more effective control strategies to prevent outbreaks of bacterial infections.

The first report of a C-type lectin contains a CLIP domain involved in antibacterial defense in Macrobrachium nipponense

We identified a novel C-type lectin (CTL) from Macrobrachium nipponense, designated as Mn-clip-Lec. It consists of 1315 bp with an open reading frame of 1098 bp, encoding a polypeptide of 365 amino acids. Mn-clip-Lec contains 6 exons and 5 introns. Mn-clip-Lec possessed a CLIP domain at the N-terminal and two carbohydrate recognition domains at the C-terminal. Interaction between Mn-clip-Lec and MnLec was found by Yeast two-hybrid analysis. The expressions of Mn-clip-Lec, MnLec, prophenoloxidase (proPO)-activating system-associated genes (MnPPAF, MnPPAE, and MnPO), and antimicrobial peptides (AMPs) (MnALF and MnCRU) were up-regulated after the challenge with Staphylococcus aureus. RNA interference (RNAi)-mediated suppression of the Mn-clip-Lec and MnLec genes in S. aureus-challenged prawns reduced the transcripts of MnPPAF, MnPPAE, MnPO, MnALF and MnCRU. Knockdown of Mn-clip-Lec and MnLec resulted in decrease in PO activity in M. nipponense infected with S. aureus. The recombinant Mn-clip-Lec (rMn-clip-Lec) protein bound all tested bacteria and agglutinated S. aureus. A sugar-binding assay revealed that rMn-clip-Lec could bind to LPS or PGN. rMn-clip-Lec accelerated the clearance of S. aureus in vivo. Our findings suggest that Mn-clip-Lec and its interacting MnLec play important roles in the induction of the proPO system and AMPs expression in M. nipponense during bacterial infection.

The Interplay of TLR-NFκB Signalling Pathway and Functional Immune-Related Enzymes in the Inflammatory Response of Ciona robusta

The close phylogenetic relationship between ascidians (Tunicata) and vertebrates makes them a powerful model for studying the innate immune system. To better understand the nature and dynamics of immune responses and the mechanisms through which bacterial infections are detected and translated into inflammation in Ciona robusta, we applied an approach combining in vivo lipopolysaccharide (LPS) stimulation, immune-labelling techniques and functional enzymatic analyses. The immunohistochemistry showed that Toll-like receptor 4 (TLR4) and nuclear factor kappa B (NFκB) were expressed during the inflammatory pharynx response 4 h post-LPS, with the formation of nodules in pharynx vessel lumen. Also, the endothelium vessels were involved in the inflammatory response. Observations of histological sections from naive and buffer-inoculated ascidians confirmed an immuno-positive response. Enzyme immune parameters-which included the activity of phenoloxidase, glutathione peroxidase, lysozyme, alkaline phosphatase and esterase-showed up-modulation 4 h after LPS injection, confirming their participation during ascidian inflammatory response. These findings provide new insights into the mechanisms underlying the LPS-induced C. robusta response and suggest that a broad innate immune mechanism, as in vertebrates, is involved in the regulation of inflammatory responses. Further findings in this direction are needed to cover knowledge gaps regarding the organized set of molecular and cellular networks involved in universal immune interactions with pathogens.

The yeast-human coevolution: Fungal transition from passengers, colonizers, and invaders

Fungi are the cause of more than a billion infections in humans every year, although their interactions with the host are still neglected compared to bacteria. Major systemic fungal infections are very unusual in the healthy population, due to the long history of coevolution with the human host. Humans are routinely exposed to environmental fungi and can host a commensal mycobiota, which is increasingly considered as a key player in health and disease. Here, we review the current knowledge on host-fungi coevolution and the factors that regulate their interaction. On one hand, fungi have learned to survive and inhabit the host organisms as a natural ecosystem, on the other hand, the host immune system finely tunes the response toward fungi. In turn, recognition of fungi as commensals or pathogens regulates the host immune balance in health and disease. In the human gut ecosystem, yeasts provide a fingerprint of the transient microbiota. Their status as passengers or colonizers is related to the integrity of the gut barrier and the risk of multiple disorders. Thus, the study of this less known component of the microbiota could unravel the rules of the transition from passengers to colonizers and invaders, as well as their dependence on the innate component of the host's immune response. This article is categorized under: Infectious Diseases > Environmental Factors Immune System Diseases > Environmental Factors Infectious Diseases > Molecular and Cellular Physiology.

Cellular and transcriptomic response to pathogenic and non-pathogenic Vibrio parahaemolyticus strains causing acute hepatopancreatic necrosis disease (AHPND) in Litopenaeus vannamei

The shrimp industry has historically been affected by viral and bacterial diseases. One of the most recent emerging diseases is Acute Hepatopancreatic Necrosis Disease (AHPND), which causes severe mortality. Despite its significance to sanitation and economics, little is known about the molecular response of shrimp to this disease. Here, we present the cellular and transcriptomic responses of Litopenaeus vannamei exposed to two Vibrio parahaemolyticus strains for 98 h, wherein one is non-pathogenic (VpN) and the other causes AHPND (VpP). Exposure to the VpN strain resulted in minor alterations in hepatopancreas morphology, including reductions in the size of R and B cells and detachments of small epithelial cells from 72 h onwards. On the other hand, exposure to the VpP strain is characterized by acute detachment of epithelial cells from the hepatopancreatic tubules and infiltration of hemocytes in the inter-tubular spaces. At the end of exposure, RNA-Seq analysis revealed functional enrichment in biological processes, such as the toll3 receptor signaling pathway, apoptotic processes, and production of molecular mediators involved in the inflammatory response of shrimp exposed to VpN treatment. The biological processes identified in the VpP treatment include superoxide anion metabolism, innate immune response, antimicrobial humoral response, and toll3 receptor signaling pathway. Furthermore, KEGG enrichment analysis revealed metabolic pathways associated with survival, cell adhesion, and reactive oxygen species, among others, for shrimp exposed to VpP. Our study proves the differential immune responses to two strains of V. parahaemolyticus, one pathogenic and the other nonpathogenic, enlarges our knowledge on the evolution of AHPND in L. vannamei, and uncovers unique perspectives on establishing genomic resources that may function as a groundwork for detecting probable molecular markers linked to the immune system in shrimp.

Crab microRNA-381-5p regulates prophenoloxidase activation and phagocytosis to promote intracellular bacteria Spiroplasma eriocheiris infection by targeting mannose-binding protein

Mannose-binding lectin plays an essential role in bacteria or virus-triggered immune response in mammals. Previous proteomic data revealed that in Eriocheir sinensis, the mannose-binding protein was differentially expressed after Spiroplasma eriocheiris infection. However, the function of mannose-binding protein against pathogen infection in invertebrates is poorly understood. In this study, a crab mannose-binding protein (EsMBP) was characterized and enhanced the host resistance to S. eriocheiris infection. The application of recombinant C-type carbohydrate recognition domain (CTLD) of EsMBP led to increased crab survival and decreased S. eriocheiris load in hemocytes. Meanwhile, the overexpression of CTLD of EsMBP in Raw264.7 cells inhibited S. eriocheiris intracellular replication. In contrast, depletion of EsMBP by RNA interference or antibody neutralization attenuated phenoloxidase activity and hemocyte phagocytosis, rendering host more susceptible to S. eriocheiris infection. Furthermore, miR-381-5p in hemocytes suppressed EsMBP expression and negatively regulated phenoloxidase activity to exacerbate S. eriocheiris invasion of hemocytes. Taken together, our findings revealed that crab mannose-binding protein was involved in host defense against S. eriocheiris infection and targeted by miR-381-5p, providing further insights into the control of S. eriocheiris spread in crabs.

Lectin diversity and their positive roles in WSSV replication through regulation of calreticulin expression and inhibiting ALFs expression

In biological evolution, gene duplication (GD) generates new genes to facilitate new functions. C-type lectins (CTLs) in crayfish have been extended by GD to expand their family members. In this study, four CTL genes generated by GD were identified from Procambarus clarkii (PcLec1-4). Among these four genes, PcLec1 can also generate new isoforms with different numbers of tandem repeats through DNA slip mispairing. PcLec1-4 was widely expressed in multiple tissues. The expression levels of PcLec1-4 were upregulated in the intestine of P. clarkii upon white spot syndrome virus (WSSV) challenge at multiple time points. Further analysis indicated that GATA transcription factor regulated PcLec1-4 expression. RNA interference and recombinant PcLec1-4 protein injection experiments suggested that PcLec1-4 promoted the expression of calreticulin (PcCRT) and negatively regulated the expression of antimicrobial peptides, thereby promoting WSSV replication. This study contributes to the understanding of the function of CTLs produced by GD during WSSV invasion in crustaceans.

Characterization of a Lipopolysaccharide- and Beta-1,3-Glucan Binding Protein (LGBP) from the Hepatopancreas of Freshwater Prawn, Macrobrachium rosenbergii, Possessing Lectin-Like Activity

The study focuses on the isolation, characterization, and expression analysis of a lectin from the hepatopancreas of Macrobrachium rosenbergii. The protein was isolated by affinity chromatography on a melibiose-agarose column. The molecular weight of the native protein was found to be ~120 kDa which consists of a single polypeptide of ~39.5 kDa. On mass spectrometric analysis, the protein was identified as lipopolysaccharide- and beta-1,3-glucan binding protein (LGBP). LGBP showed hemagglutination with rabbit RBC like a lectin and its carbohydrate-binding specificity was determined by the hemagglutination inhibition test. The protein also showed antibacterial activity against two Gram-negative bacteria Vibrio harveyi and Aeromonas sobria, and one Gram positive bacteria Bacillus cereus in the disc diffusion test. Rabbit antiserum was raised against the purified LGBP and used to develop a sandwich ELISA system for quantitation of the protein in hepatopancreas and serum samples of M. rosenbergii. The expression of the LGBP transcripts in muscle, hepatopancreas, and gill tissues from M. rosenbergii juveniles at 72 h post-challenge of V. harveyi was not modulated as noticed in qPCR analysis. However, significant increases in the concentrations of LGBP protein in hepatopancreas (5.23 ± 0.45 against 3.43 ± 0.43 mg/g tissue in control) and serum (1.08 ± 0.14 against 0.61 ± 0.08 µg/ml in control) were observed in the challenged group of prawns in ELISA suggesting its putative role against bacterial infections. The study for the first time characterized the native LGBP of M. rosenbergii showing a multifunctional role in immunity.

The immunomodulatory and antioxidant effects of β-glucans in invertebrates

β-glucans (βGs) are carbohydrate polymers linked by β-1,3, 1,4 or 1,6 bonds, they have been used to protect against potential pathogens and prevent lethal diseases. The immune system possesses several receptors that identify a wide range of structures and trigger cellular and humoral mechanisms. However, the mechanisms by which βGs activate the immune system of invertebrate organisms have not been fully clarified. This review is focused on evaluating the effect of βGs on innate immune system in invertebrates. βGs stimulate different cellular and humoral mechanisms, such as phagocytosis, oxygen species production, extracellular trap formation, proPO system, and antimicrobial peptide synthesis, moreover, βGs increase survival rate and decrease pathogen load in several species.

Quantification of proteomic profile changes in the hemolymph of crayfish during in vitro coagulation

Hemolymph is the circulatory fluid that fills the body cavity of crustaceans, analogous to blood in vertebrates. Hemolymph coagulation, similar to blood clotting in vertebrates, plays a crucial role in wound healing and innate immune responses. Despite extensive studies on the clotting process in crustaceans, no comparative quantitative analysis of the protein composition of non-clotted and clotted hemolymph in any decapod has been reported. In this study, we used label-free protein quantification with high-resolution mass spectrometry to identify the proteomic profile of hemolymph in crayfish and quantify significant changes in protein abundances between non-clotted and clotted hemolymph. Our analysis identified a total of two-hundred and nineteen proteins in both hemolymph groups. Furthermore, we discussed the potential functions of the top most high and low-abundant proteins in hemolymph proteomic profile. The quantity of most of the proteins was not significantly changed during coagulation between non-clotted and clotted hemolymph, which may indicate that clotting proteins are likely pre-synthesized, allowing for a swift coagulation response to injury. Four proteins still showed abundance differences (p < 0.05, fold change>2), including C-type lectin domain-containing proteins, Laminin A chain, Tropomyosin, and Reverse transcriptase domain-containing proteins. While the first three proteins were down-regulated, the last one was up-regulated. The down-regulation of structural and cytoskeletal proteins may affect the process of hemocyte degranulation needed for coagulation, while the up-regulation of an immune-related protein might be attributed to the phagocytosis ability of viable hemocytes during coagulation.

Injection administration of mangosteen, Garcinia mangostana, husk extract enhances physiological and immune-neuroendocrinological regulation of Macrobrachiumrosenbergii

The study aimed to investigate the effects of injecting mangosteen husk hot-water extracts (MHE) on immune and physiological factors in Macrobrachium rosenbergii. Different doses of MHE (10, 20, and 40 μg prawn-1) were injected into the prawns, and various immune and physiological parameters were evaluated. The results revealed that higher doses of MHE (20 and 40 μg prawn-1) led to significant increases in immune parameters, improved phagocytic activity, and clearance efficiency. However, certain parameters, such as phenoloxidase activity per granulocyte, plasma glucose, and lactate levels were decreased after injection. Moreover, prawns injected with MHE and subjected to hypothermal stress exhibited changes in haemolymph dopamine and norepinephrine. Prawns injected with MHE for 7 days showed increased survival rates when challenged with Lactococcus garvieae. The relative survival percentages were 11.8%, 46.6%, and 47.1% for MHE doses of 10, 20, and 40 μg prawn-1 injection, respectively, indicating enhanced resistance to the pathogen. In conclusion, injecting MHE can act as an immunostimulant and physiological and neuroendocrine regulator for prawns, enhancing their resistance to L. garvieae.

Epigenetic Modulations for Prevention of Infectious Diseases in Shrimp Aquaculture

Aquaculture assumes a pivotal role in meeting the escalating global food demand, and shrimp farming, in particular, holds a significant role in the global economy and food security, providing a rich source of nutrients for human consumption. Nonetheless, the industry faces formidable challenges, primarily attributed to disease outbreaks and the diminishing efficacy of conventional disease management approaches, such as antibiotic usage. Consequently, there is an urgent imperative to explore alternative strategies to ensure the sustainability of the industry. In this context, the field of epigenetics emerges as a promising avenue for combating infectious diseases in shrimp aquaculture. Epigenetic modulations entail chemical alterations in DNA and proteins, orchestrating gene expression patterns without modifying the underlying DNA sequence through DNA methylation, histone modifications, and non-coding RNA molecules. Utilizing epigenetic mechanisms presents an opportunity to enhance immune gene expression and bolster disease resistance in shrimp, thereby contributing to disease management strategies and optimizing shrimp health and productivity. Additionally, the concept of epigenetic inheritability in marine animals holds immense potential for the future of the shrimp farming industry. To this end, this comprehensive review thoroughly explores the dynamics of epigenetic modulations in shrimp aquaculture, with a particular emphasis on its pivotal role in disease management. It conveys the significance of harnessing advantageous epigenetic changes to ensure the long-term viability of shrimp farming while deliberating on the potential consequences of these interventions. Overall, this appraisal highlights the promising trajectory of epigenetic applications, propelling the field toward strengthening sustainability in shrimp aquaculture.

Transcriptome analysis of Macrobrachium rosenbergii hemocytes in response to Staphylococcus aureus infection

The aquaculture industry has suffered significant financial losses as a result of disease outbreaks. In particular, disease outbreaks have become a major problem that can seriously affect the sustainable development of the Macrobrachium rosenbergii aquaculture industry. It is crucial to determine the defense mechanism of the host after pathogenic invasion in order to provide effective defense measures after disease outbreaks. Shrimp, like other invertebrates, primarily depend on their innate immune systems to defend against pathogens, and recognize and resist pathogens through humoral and cellular immune responses. In this investigation, we used RNA-seq technology to investigate the transcriptome of hemocytes from M. rosenbergii induced by Staphylococcus aureus. Our main targets were immune pathways and genes related to innate immunity. RNA-seq identified 209,069 and 204,775 unigenes in the control and experimental groups, respectively. In addition, we identified 547 and 1734 differentially expressed genes (DEGs) following S. aureus challenge after 6 and 12 h (h), respectively. GO and KEGG enrichment analysis revealed that the DEGs were significantly enriched in several biological signalling pathways, including NOD-like receptor, PI3K-Akt, Toll and Imd, IL-17, TGF-beta, RIG-I-like receptor, cAMP, apoptosis, and C-type lectin receptor. Sixteen DEGs were chosen at random for qPCR verification; these results concurred with those from sequencing. Our findings revealed that immune-related genes play an important role in antibacterial activities and have specific functions for gram-positive bacteria. These results provide more data for the prevention of M. rosenbergii diseases and offer a basis for the better prevention of diseases.

Granules of immune cells are the source of organelles in the regenerated nerves of crayfish antennae

Regeneration refers to the regrowing and replacing of injured or lost body parts. Crayfish antennae are nervous organs that are crucial for perceiving environmental signals. Immune cells (hemocytes) are responsible for neurogenesis in crayfish. Here, we used transmission electron microscopy to investigate at ultrastructural levels the potential roles of immune cells in nerve regeneration in crayfish antennae after amputation. The results showed that, while all three types of hemocytes were observed during nerve regeneration, granules of semi-granulocytes and granulocytes are the main sources of new organelles such as mitochondria, the Golgi apparatus and nerve fibres in the regenerated nerves of crayfish antennae. We describe the transformation of immune cell granules into different organelles in the regenerating nerve at ultrastructural levels. Also, we observed that the regeneration process speeds up after crayfish moulting. In conclusion, the granules are compacted packages of versatile materials carried by immune cells and can be converted into different organelles during nerve regeneration in crayfish antennae.

Lactobacillus plantarum isolated from kefir enhances immune responses and survival of white shrimp (Penaeus vannamei) challenged with Vibrio alginolyticus

Lactobacillus plantarum is known for its probiotics benefit to host, although the effects vary among strains. This study conducted a feeding experiment of three Lactobacillus strains, MRS8, MRS18 and MRS20, which were isolated from kefir and incorporated into the diets of shrimp to evaluate the effects of non-specific immunity, immune-related gene expression, and disease resistance of white shrimp (Penaeus vannamei) against Vibrio alginolyticus. To prepare the experimental feed groups, the basic feed was mixed with different concentrations of L. plantarum strains MRS8, MRS18, and MRS 20, which were incorporated at 0 CFU (control), 1 × 10⁶ CFU (groups 8-6, 18-6, and 20-6), and 1 × 10⁹ CFU (groups 8-9, 18-9, and 20-9) per gram of diet for an in vivo assay. During the rearing period for 28 days of feeding each group, immune responses, namely the total hemocyte count (THC), phagocytic rate (PR), phenoloxidase activity, and respiratory burst were examined on days 0, 1, 4, 7, 14, and 28. The results showed that groups 20-6, 18-9 and 20-9 improved THC, and groups 18-9 and 20-9 improved phenoloxidase activity and respiratory burst as well. The expression of immunity-related genes was also examined. Group 8-9 increased the expression of LGBP, penaeidin 2 (PEN2) and CP, group 18-9 increased the expression of proPO1, ALF, Lysozyme, penaeidin 3 (PEN3) and SOD, and group 20-9 increased the expression of LGBP, ALF, crustin, PEN2, PEN3, penaeidin 4 (PEN4) and CP (p < 0.05). Groups 18-6, 18-9, 2-6, and 20-9 were further used in the challenge test. After feeding for 7 days and 14 days, Vibrio alginolyticus was injected into white shrimp and observed the shrimp survival for 168 h. The results showed that compared to the control, all groups improved the survival rate. Especially, feeding group 18-9 for 14 days improved the survival rate of white shrimp (p < 0.05). After the challenge test for 14 days, the midgut DNA of survival white shrimps was extracted to analyze the colonization of L. plantarum. Among the groups, (6.61 ± 3.58) × 10⁵ CFU/pre shrimp of L. plantarum in feeding group 18-9 and (5.86 ± 2.27) × 10⁵ CFU/pre shrimp in group 20-9 were evaluated by qPCR. Taken together, group 18-9 had the best effects on the non-specific immunity, the immune-related gene expression, and the disease resistance, which might be due to the benefit of the probiotic colonization.

Effectiveness of various cacao pod husk extraction byproducts in promoting growth and immunocompetence in Litopenaeus vannamei

Extracts from plant products can promote growth, can act as immunostimulants, and have antibacterial and antiparasitic properties. These extracts can be used as alternatives to the chemical treatments commonly used to prevent and control disease in aquatic species. Research on the subject has focused on identifying invasive plants or agricultural waste products that can be used as immunostimulants. The present study further identified an optimal means of extracting pectin from cacao pod husks to promote growth performance and immunocompetence in Litopenaeus vannamei that would both reduce production costs and enable waste recycling. The byproducts of pectin extraction from cacao pod husks, that is, dried cacao pod husk powder (DCP), steamed DCP (sDCP), hot water-treated cacao pod husk powder (HCP), hot water-treated cacao pod husk supernatant (HCS), and cacao pod husk pectin (CPH pectin), were used to create five experimental diets, which were administered to five groups. The control group was fed a basal diet. The growth and immunocompetence of the shrimp were determined after 30, 60, 90 and 120 days of feeding. To identify the most cost-effective means of obtaining dried cacao pod husks, this study firstly determined the costs and effectiveness of the sun-drying, dehumidification, and heated-wind drying techniques. According to the results of growth performance, the CPH pectin group had higher survival but lower weight gain than the DCP, sDCP, HCP, and HCS groups did. At 30, 60, and 90 days, the clearance efficiency of the experimental groups was higher than that of the control group. At 60 days, the experimental groups had significantly higher phagocytic activity than the control group did. However, at 30 and 90 days the HCP, HCS and CPH pectin group had higher phagocytic activity. The total hemocyte count, differential hemocyte count, phenoloxidase activity, and respiratory bursts of the CPH pectin group were higher at 30 days but the same as those of the control group at 60 and 90 days. After 120 days of feeding trial, the resistance of L. vannamei fed with diets containing byproducts of pectin extraction from cacao pod husks significantly enhanced compared to that in BD group when they were infected with Vibrio aliginolyticus for 168 h, and the related higher survival rate can be observed in HCP, HCS and CPH pectin groups. The study findings suggest that diet-administered HCP and HCS have long-term immunostimulant potential and that CPH pectin has potential in the early stages of feeding. In addition, when heated air drying was employed, a moisture level of below 10% was obtained within 12 h. The results of this study indicate that adding HCP obtained from heated air-dried cacao pod husks to the feed of L. vannamei is the most cost-effective and sustainable means of promoting long-term growth performance and immunocompetence in the species.

Effects of environmental factors on the cellular and molecular parameters of the immune system in decapods

Crustaceans and in particular decapods (i.e. shrimp, crabs and lobsters) are a diverse, commercially and ecologically important group of organisms. They are exposed to a range of environmental factors whose abiotic and biotic components are prone to fluctuate beyond their optimum ranges and, in doing so, affect crustaceans' immune system and health. Changes in key environmental factors such as temperature, pH, salinity, dissolved oxygen, ammonia concentrations and pathogens can provoke stress and immune responses due to alterations in immune parameters. The mechanisms through which stressors mediate effects on immune parameters are not fully understood in decapods. Improved knowledge of the environmental factors - above all, their abiotic components - that influence the immune parameters of decapods could help mitigate or constrain their harmful effects that adversely affect the production of decapod crustaceans. The first part of this overview examines current knowledge and information gaps regarding the basic components and functions of the innate immune system of decapods. In the second part, we discuss various mechanisms provoked by environmental factors and categorize cellular and molecular immune responses to each environmental factor with special reference to decapods.

Impact of Dietary Administration of Seaweed Polysaccharide on Growth, Microbial Abundance, and Growth and Immune-Related Genes Expression of The Pacific Whiteleg Shrimp (Litopenaeus vannamei)

This work aims to determine the impact of dietary supplementation of polysaccharide, extracted from brown seaweeds Sargassum dentifolium on growth indices, feed utilization, biochemical compositions, microbial abundance, expressions of growth and immunity-related genes, and stress genes of the Pacific Whiteleg shrimp Litopenaeus vannamei. A total of 360 post-larvae of L. vannamei were randomly distributed into a 12-glass aquarium (40 L of each) at a stocking density of 30 shrimp with an initial weight of (0.0017 ± 0.001 g). During the 90-day experiment trial, all shrimp larvae were fed their respective diets at 10% of total body weight, three times a day. Three experimental diets were prepared with different seaweed polysaccharide (SWP) levels. The basal control diet had no polysaccharide level (SWP₀), while SWP₁, SWP₂, and SWP₃ contained polysaccharides at concentrations of 1, 2, and 3 g kg^-1 diet, respectively. Diets supplemented with polysaccharide levels showed significant improvements in weight gain and survival rate, compared to the control diet. Whole-body biochemical composition and the microbial abundance (the total count of heterotrophic bacteria and Vibrio spp.) of L. vannamei showed significant differences among polysaccharide-treated diets compared to the control. At the end of the feeding experiment, the dietary supplementation of polysaccharide levels enhanced the expression of growth-related genes (Insulin-like growth factors (IGF-I, IGF-II), immune-related genes (β -Glucan-binding protein (β-Bgp), Prophenoloxidase (ProPO), Lysozyme (Lys), and Crustin), and stress genes (Superoxide dismutase (SOD) and Glutathione peroxidase (GPx) in the muscle tissue of L. vannamei. However, the current study concluded that the inclusion rate of 2 g kg^-1 of polysaccharide as a dietary additive administration enhanced both weight gain and survival rate of L. vannamei, while the incorporation level of 3 g kg^-1 reduces the abundance of pathogenic microbes and enhances the growth-, immunity- and stress-related gene expressions of L. vannamei.

White spot syndrome virus impact on the expression of immune genes and gut microbiome of black tiger shrimp Penaeus monodon

The gut microbiome plays an essential role in the immune system of invertebrates and vertebrates. Pre and pro-biotics could enhance the shrimp immune system by increasing the phenoloxidase (PO), prophenoloxidase (ProPO), and superoxide dismutase activities. During viral infection, the host immune system alteration could influence the gut microbiome composition and probably lead to other pathogenic infections. Since the JAK/STAT pathway is involved in white spot syndrome virus (WSSV) infection, we investigated the intestine immune genes of STAT-silenced shrimp. During WSSV infection, expression levels of PmVago1, PmDoral, and PmSpätzle in PmSTAT-silenced shrimp were higher than normal. In addition, the transcription levels of antimicrobial peptides, including crustinPm1, crustinPm7, and PmPEN3, were higher in WSSV-challenged PmSTAT-silenced shrimp than the WSSV-infected normal shrimp. Meanwhile, PmSTAT silencing suppressed PmProPO1, PmProPO2, and PmPPAE1 expressions during WSSV infection. The microbiota from four shrimp tested groups (control group, WSSV-infected, PmSTAT-silenced, and PmSTAT-silenced infected by WSSV) was significantly different, with decreasing richness and diversity due to WSSV infection. The relative abundance of Bacteroidetes, Actinobacteria, and Planctomycetes was reduced in WSSV-challenged shrimp. However, at the species level, P. damselae, a pathogen to human and marine animals, significantly increased in WSSV-challenged shrimp. In constrast, Shewanella algae, a shrimp probiotic, was decreased in WSSV groups. In addition, the microbiota structure between control and PmSTAT-silenced shrimp was significantly different, suggesting the importance of STAT to maintain the homeostasis interaction with the microbiota.

PvML1 suppresses bacterial infection by recognizing LPS and regulating AMP expression in shrimp

Toll and Toll-like receptors (TLRs) play essential roles in the innate immunity of Drosophila and mammals. Recent studies have revealed the presence of Toll-mediated immune signaling pathways in shrimp. However, the recognition and activation mechanism of Toll signaling pathways in crustaceans remain poorly understood due to the absence of key recognition molecules, such as peptidoglycan recognition proteins. Here, a novel MD2-related lipid-recognition (ML) member named PvML1 was characterized in Penaeus vannamei. We found that PvML1 shared a similar 3D structure with human MD2 that could specifically recognize lipopolysaccharides (LPS) participating in LPS-mediated TLR4 signaling. PvML1 was highly expressed in hemocytes and remarkably upregulated after Vibrio parahemolyticus challenge. Furthermore, the binding and agglutinating assays showed that PvML1 possessed strong binding activities to LPS and its key portion lipid A as well as Vibrio cells, and the binding of PvML1 with bacterial cells led to the agglutination of bacteria, suggesting PvML1 may act as a potential pathogen recognition protein upon interaction with LPS. Besides, coating V. parahemolyticus with recombinant PvML1 promoted bacterial clearance in vivo and increased the survival rate of bacterium-challenged shrimp. This result was further confirmed by RNAi experiments. The knockdown of PvML1 remarkably suppressed the clearance of bacteria in hemolymph and decreased the survival rate of infected shrimp. Meanwhile, the silencing of PvML1 severely impaired the expression of a few antimicrobial peptides (AMPs). These results demonstrated the significant correlation of bacterial clearance mediated by PvML1 with the AMP expression. Interestingly, we found that PvML1 interacted with the extracellular region of PvToll2, which had been previously shown to participate in bacterial clearance by regulating AMP expression. Taken together, the proposed antibacterial model mediated by PvML1 might be described as follows. PvML1 acted as a potential recognition receptor for Gram-negative bacteria by binding to LPS, and then it activated PvToll2-mediated signaling pathway by interacting with PvToll2 to eliminate invading bacteria through producing specific AMPs. This study provided new insights into the recognition and activation mechanism of Toll signaling pathways of invertebrates and the defense functions of ML members.

Full-length transcriptome sequencing and comparative transcriptome analysis of Eriocheir sinensis in response to infection by the microsporidian Hepatospora eriocheir

As a new generation of high-throughput sequencing technology, PacBio Iso-Seq technology (Iso-Seq) provides a better alternative sequencing method for the acquisition of full-length unigenes. In this study, a total of 22.27 gigabyte (Gb) subread bases and 128,614 non-redundant unigenes (mean length: 2,324 bp) were obtained from six main tissues of Eriocheir sinensis including the heart, nerve, intestine, muscle, gills and hepatopancreas. In addition, 74,732 unigenes were mapped to at least one of the following databases: Non-Redundant Protein Sequence Database (NR), Gene Ontology (GO), Kyoto Encyclopaedia of Genes and Genomes (KEGG), KEGG Orthology (KO) and Protein family (Pfam). In addition, 6696 transcription factors (TFs), 28,458 long non-coding RNAs (lncRNAs) and 94,230 mRNA-miRNA pairs were identified. Hepatospora eriocheir is the primary pathogen of E. sinensis and can cause hepatopancreatic necrosis disease (HPND); the intestine is the main target tissue. Here, we attempted to identify the key genes related to H. eriocheir infection in the intestines of E. sinensis. By combining Iso-Seq and Illumina RNA-seq analysis, we identified a total of 12,708 differentially expressed unigenes (DEUs; 6,696 upregulated and 6,012 downregulated) in the crab intestine following infection with H. eriocheir. Based on the biological analysis of these DEUs, several key processes were identified, including energy metabolism-related pathways, cell apoptosis and innate immune-related pathways. Twelve selected genes from these DEUs were subsequently verified by quantitative real-time PCR (qRT-PCR) analysis. Our findings enhance our understanding of the E. sinensis transcriptome and the specific association between E. sinensis and H. eriocheir infection.

Aquaculture sustainability through alternative dietary ingredients: Microalgal value-added products

Aquaculture contributes remarkably to the global economy and food security through seafood production, an important part of the global food supply chain. The success of this industry depends heavily on aquafeeds, and the nutritional composition of the feed is an important factor for the quality, productivity, and profitability of aquaculture species. The sustainability of the aquaculture industry depends on the accessibility of quality feed ingredients, such as fishmeal and fish oil. These traditional feedstuffs are under increasing significant pressure due to the rapid expansion of aquaculture for human consumption and the decline of natural fish harvest. In this review, we evaluated the development of microalgal molecules in aquaculture and expanded the use of these high-value compounds in the production of aquaculture diets. Microalgae-derived functional ingredients emerged as one of the promising alternatives for aquafeed production with positive health benefits. Several compounds found in microalgae, including carotenoids (lutein, astaxanthin, and β-carotene), essential amino acids (leucine, valine, and threonine), β-1-3-glucan, essential oils (docosahexaenoic acid and eicosapentaenoic acid), minerals, and vitamins, are of high nutritional value to aquaculture.

Effects of dietary Clostridium autoethanogenum protein on the growth, disease resistance, intestinal digestion, immunity and microbiota structure of Litopenaeus vannamei reared at different water salinities

The shortage of fishmeal (FM) resources limits the healthy development of aquaculture. Developing new protein sources to replace FM in aquatic feeds is an effective measure to alleviate this situation. However, the application effect of new protein sources is greatly affected by water salinity, which is an important parameter of aquaculture. In this study, the growth, disease resistance, and intestinal digestion, immunity, and microbiota structure of Litopenaeus vannamei (initial weight: 0.38 ± 0.01 g) fed on Clostridium autoethanogenum protein (CAP) or not at three different water salinities (15 ‰, 30 ‰, and 45 ‰) were compared, aiming to explore the effects of dietary CAP on shrimp when suffering different salinity stresses. The results showed that the growth performance, feed utilization, and survival rate (SR) after pathogen challenge of L. vannamei could be significantly improved by dietary CAP when compared with the control at the same salinity and they were also significantly affected by salinity changes when L. vannamei was fed on the same protein source. With the increase in salinity, obvious upregulation was observed in the activities and gene expression of digestive enzymes both in L. vannamei fed on FM and CAP, with significantly higher levels in L. vannamei fed on CAP than in those fed on FM at the same salinity. Meanwhile, the expression levels of immune genes in the CAP group were significantly higher than those in the FM group at different salinities. The intestinal microbiota analysis showed that CAP could increase the relative abundance of beneficial bacteria and decrease the relative abundance of harmful bacteria in the intestine of L. vannamei at the phylum, family, and genus levels, and it was more affected by salinity changes when compared with FM. Besides, the changes in salinity and protein sources led to different changes in the intestinal microflora function of L. vannamei. In sum, this study indicated that CAP could improve the growth, disease resistance, digestive capacity, and intestinal microflora of L. vannamei with a much more intense immune response and enhance its ability to cope with salinity stress.

Heat Shock Protein 70 Is a Damage-Associated Molecular Pattern That by Binding to Lipopolysaccharide and β-1,3-Glucan-Binding Protein Activates the Prophenoloxidase System in Shrimp

Recent studies have initiated a paradigm shift in understanding heat shock protein 70 (HSP70) functions in the shrimp immune system. However, the mechanism by which Litopenaeus vannamei (Lv)HSP70 modulates the innate immune response remains unclear. This study shows that LvHSP70 binds to the pattern recognition receptor LPS and β-1,3-glucan-binding protein (LvLGBP), and subsequently leads to the activation of the prophenoloxidase system. Injection of shrimp with rLvHSP70 significantly (p < 0.05) upregulated the gene and protein expression of the key pattern recognition receptor LvLGBP. A coimmunoprecipitation and ELISA-based binding assay strongly confirmed the binding of LvHSP70 to LvLGBP at polysaccharide recognition motifs (PLS motifs) with a Kd of 4.44 μM and its competitive binding with LPS (IC50) is 8.036 μM. Conversely, LPS efficiently competed with LvHSP70 for binding to LvLGBP in a concentration-dependent manner with an IC50 of 7.662 μM, indicating that both are ligands of LvLGBP and likely bind at the same site. Binding of LvHSP70 to LvLGBP highly activated phenoloxidase activity in shrimp hemocyte lysate supernatants. Gene silencing of LvLGBP impaired the activation of phenoloxidase activity in shrimp by rLvHSP70, indicating that LvHSP70-LvLGBP interaction was essential for stimulating the immune cascade. Taken together, these results demonstrated that LvHSP70 is a ligand of LvLGBP similar to LPS and acts as a damage-associated molecular pattern to modulate the shrimp immune system via the prophenoloxidase system, eventually leading to the production of melanin and toxic reactive intermediates against invading pathogens.

Control of vibriosis in shrimp through the management of the microbiota and the immune system

Shrimp aquaculture is constantly threatened by recurrent outbreaks of diseases caused by pathogenic bacteria of the genus Vibrio. Acute hepatopancreatic necrosis disease (AHPND) is one of the most aggressive vibriosis reported to date in the shrimp industry. AHPND provokes massive mortalities, causing economic losses with strong social impacts. Control of vibriosis requires the application of multifactorial strategies. This includes vibrio exclusion, shrimp microbiota, particularly in the digestive tract, and shrimp health management through immune stimulation. This paper reviews these two strategies for the prophylactic control of vibriosis. First, we describe the devastating effects of AHPND and the cellular and humoral effectors of the shrimp immune system to cope with this pathology. Secondly, the mechanisms of action of probiotics and their positive impacts are highlighted, including their immunostimulant effects and their role in the balance of the shrimp microbiota. Finally, we reviewed immunostimulants and prebiotics polysaccharides that together with probiotics act benefiting growth, feed efficiency and the microbiota of the digestive tract of farmed shrimp.

In vivo study of a novel protein kinase C that mediates immunocompetence and catecholamine biosynthesis in hemocytes of Litopenaeus vannamei by using its potential competitive inhibitor, bisindolylmaleimide I

This study applied bisindolylmaleimide I (BSM), a pharmacological competitive inhibitor of protein kinase C (PKC) enzymatic activity, at 1.25 pmol shrimp^-1 for 60 min to investigate the potential involvement of PKC in signal transduction pathways in the hemocytes of Litopenaeus vannamei. A novel PKC in L. vannamei (LvnPKC) was identified and characterized and was determined to be involved in mediating the neuroendocrine-immune regulatory network. The hemocytes of L. vannamei that receive BSM exhibit significantly decreased PKC activity and LvnPKC gene and protein expression levels. Furthermore, the total hemocyte count, hyaline cells, and semigranular cells increased significantly along with significant decreases in granular cells, and meanwhile, the significantly increased phenoloxidase activity, respiratory bursts, superoxide dismutase (SOD) activity, phagocytic activity, and neutrophil extracellular trap were observed; however, phagocytic activity decreased significantly. In a molecular model, the gene expressions of lipopolysaccharide- and β-1,3-glucan-binding protein, peroxinectin, cytosolic manganese SOD, mitochondrial manganese SOD, and copper/zinc SOD in the hemocytes of L. vannamei that had received BSM decreased significantly, but prophenoloxidase I increased significantly. In catecholamine biosynthesis, tyrosine, dopamine, and norepinephrine decreased significantly in the hemocytes of L. vannamei that had received BSM, and l-dihydroxyphenylalanine increased. Moreover, tyrosine hydroxylase (TH) activity increased significantly, whereas TH and dihydroxyphenylalanine decarboxylase gene expression decreased significantly. These findings suggest that BSM inhibits PKC activity in hemocytes in which LvnPKC gene and protein expression are also inhibited. Additionally, the hemocytes' immunocompetence, including their prophenoloxidase and antioxidant systems, phagocytic activity, and catecholamine biosynthesis, was disrupted, confirming the roles of LvnPKC in mediating the neuroendocrine-immune regulatory network in hemocytes.

The Combined Use of Pediococcus pentosaceus and Fructooligosaccharide Improves Growth Performance, Immune Response, and Resistance of Whiteleg Shrimp Litopenaeus vannamei Against Vibrio parahaemolyticus

In this study, we evaluated the effect of probiotic bacteria Pediococcus pentosaceus supplemented at different inclusion levels in a control diet [basal diet containing 0.5% fructooligosaccharide (FOS)] on the growth performance, feed conversion ratio, immune response, and the disease resistance of whiteleg shrimp Litopenaeus vannamei juveniles against Vibrio parahaemolyticus. A control diet with 0.5% FOS but without P. pentosaceus supplementation (Control) was prepared. In addition, three other test diets were also formulated: control diet supplemented with P. pentosaceus at (i) 1 × 106 cfu g-1 diet (P1), (ii) 1 × 107 cfu g-1 diet (P2), or (iii) 1 × 108 cfu g-1 diet (P3). After a 60-day feeding trial, the experimental shrimps were challenged with V. parahaemolyticus. The results showed that dietary supplementation of P. pentosaceus significantly improved the growth performance and immune responses of L. vannamei juveniles. The juveniles that were fed with a P2 or P3 diet recorded the maximum increase in the final body weight, final length, weight gain, and survival rate. The total hemocyte counts, phenoloxidase, and lysozyme activity of shrimp fed with either of these two diets were significantly enhanced. The results also showed that juveniles fed with a P2 or P3 diet exhibited significantly lower mortality when challenged with V. parahaemolyticus. Overall results suggested that a combination of P. pentosaceus at the inclusion level of 1 × 107 cfu g-1 diet (P2) and 0.5% FOS could be considered as a potential synbiotic formulation for improving the growth, health, and robustness of L. vannamei.

A synbiotic containing prebiotic prepared from a by-product of king oyster mushroom, Pleurotus eryngii and probiotic, Lactobacillus plantarum incorporated in diet to improve the growth performance and health status of white shrimp, Litopenaeus vannamei

This study aimed to evaluate the effects of a synbiotic composite an extract from a by-product of king oyster mushroom, Pleurotus eryngii (KOME), and probiotic Lactobacillus plantarum 7-40 on the growth performance and health status of white shrimp, Litopenaeus vannamei. The KOME was able to stimulate the growth of probiotic, but not the growth of Vibrio pathogens, including V. alginolyticus, V. parahaemolyticus, and V. harveyi. Four diets were formulated, including a control diet supplemented without prebiotic and probiotic, a basal diet supplemented with KOME (5 g kg^-1) (ME), a basal diet supplemented with probiotic (1 × 10⁸ CFU kg^-1) (LP), and a basal diet supplemented with KOME (5 g kg^-1) and probiotic (1 × 10⁸ CFU kg^-1) (SYN). Shrimp fed the ME, LP, and SYN diets had significantly higher survival than that of shrimp fed with the control diet for 8 weeks. Shrimp in the SYN group also had a significantly higher weight gain and total final weight in comparison with the control and other treatments. In the intestinal tract, lactic acid bacteria count was significantly higher in the SYN group, whereas the Vibrio-like bacteria count was significantly higher in the ME group than in the control group. For the health status assessment, the disease resistance of shrimp against V. alginolyticus was improved in all treatments compared to the shrimp in control. Shrimps in the SYN group had significantly lower cumulative mortality due to the significant increase in immune responses, including phenoloxidase, respiratory burst, and lysozyme activity, and the gene expression of pexn and pen4 in the haemocytes, and lgbp, sp, propoii, pexn, pen3a, pen4, and gpx in the haepatopancreas of shrimp as compared to the control. Therefore, it is suggested that a combination of KOME and probiotics can be used as a synbiotic to improve the growth performance and reduce the risk of infectious diseases caused by Vibrio and at the same time significantly contribute to the circular economy.

A novel C-type lectin LvCTL 4.2 has antibacterial activity but facilitates WSSV infection in shrimp (L. vannamei)

Glycan-binding protein C-type lectin (CTL), one of the pattern recognition receptors (PRRs), binds to carbohydrates on the surface of pathogens and elicits antimicrobial responses in shrimp innate immunity. The objective was to identify and characterize a novel C-type lectin LvCTL 4.2 in Litopenaeus vannamei. The LvCTL 4.2 protein consisted of a signal peptide at the N terminal and a carbohydrate-recognition domain (CRD) with a mutated mannose-binding (Glu-Pro-Ala; EPA) motif at the C terminal, and thereby has a putative secreted mannose-binding C-type lectin architecture. LvCTL 4.2 was highly expressed in nervous tissue and stomach. Infection with white spot syndrome virus (WSSV) induced expression of LvCTL 4.2 in shrimp stomach at 12 h post infection. Conversely, there was no obvious upregulation in expression of LvCTL 4.2 in stomach or hepatopancreas of shrimp with AHPND (acute hepatopancreas necrosis disease). Pathogen binding assays confirmed recombinant LvCTL 4.2 protein (rLvCTL 4.2) had significant binding ability with the WSSV virion, Gram-negative, and Gram-positive bacteria. Moreover, rLvCTL 4.2 had strong growth inhibition of Vibrio parahaemolyticus. Silencing LvCTL 4.2 suppressed WSSV replication, whereas pretreatment of WSSV with rLvCTL 4.2 facilitated viral replication in vivo. In conclusion, LvCTL 4.2 acted as a PRR that inhibited AHPND-causing bacteria, but facilitated WSSV pathogenesis.

Dietary administration of tyramine upregulates on immune resistance, carbohydrate metabolism, and biogenic amines in Macrobrachium rosenbergii

Survival rates of prawn, Macrobrachium rosenbergii, against Lactococcus garvieae, immune parameters, carbohydrate metabolism and biogenic amines were determined when the prawn were fed diets containing tyramine (TA) at the levels of 1 and 10 mg kg^-1. Results showed that prawn fed diets containing TA for 3 days, challenged with L. garvieae, and then continuously fed individually tested diets had a significantly higher survival rate than those fed the control diet at 168 h after the challenge, in a dose-dependent manner. Results included significant increases in total haemocyte count (THC), granular cells (GCs), semigranular cells (SGCs), phenoloxidase (PO) activity, respiratory bursts (RBs), RBs per haemocyte, phagocytic activity, and clearance efficiency to L. garvieae. Significantly lower plasma glucose and lactate were observed in prawn fed with TA-containing diets for 3 days, a result consistent with increases in the survival rate of the challenge test and the haemolymph octopamine (OA) level. Haemolymph dopamine (DA), norepinephrine (NE), TA, and OA levels of prawn that were fed TA-supplemented diets increased significantly after 1 day, and OA level increased continuously until the third day with a dose-effect relationship. It is therefore concluded that TA can be absorbed from a TA-containing diet to elevate haemolymph TA level, inducing the release of DA, NE, and OA to maintain homeostasis. The higher, more extensive OA expression promoted carbohydrate metabolism and immune resistance in M. rosenbergii.

The conservation and diversity of ascidian cells and molecules involved in the inflammatory reaction: The Ciona robusta model

Ascidians are marine invertebrate chordates belonging to the earliest branch (Tunicata) in the chordate phylum, therefore, they are of interest for studying the evolution of immune systems. Due to the known genome, the non-colonial Ciona robusta, previously considered to be C. intestinalis type A, is a model species for the study of inflammatory response. The internal defense of ascidians mainly relies on hemocytes circulating in the hemolymph and pharynx. Hemocytes can be in vivo challenged by LPS injection and various granulocyte and vacuolated cell populations differentiated to produce and release inflammatory factors. Molecular biology and gene expression studies revealed complex defense mechanisms involving different inflammatory hemocytes. Furthermore, cloning procedures allowed sequence analyses and molecular studies disclose immune-related gene families including TOLL-like receptors, galectins, C-type lectins, collectins, interlectins, pentraxine-like, peroxinectins, complement factors-like, TNFα-like, IL-17-like, TGF-like, MIF-like. These genes are promptly upregulated by the inflammatory stimulus and show a time course of transcription similar to each other. Domains sequence similarity and phylogenetic relationships with the vertebrate counterparts are shedding some light on immune-related gene evolution. Selective bioassays as well as bioinformatic approaches have allowed the characterization of antimicrobial peptides and the identification of post transcriptional molecular mechanisms able of influencing dynamics of gene regulation are described. In synthesis, the purpose of this article is to further explore the topic of hemocyte and molecules related to internal defence of ascidians involved in the inflammatory reaction, as well as to discuss current and future study options through a detailed literature review.

β-glucan as a promising food additive and immunostimulant in aquaculture industry

The use of antibiotics in aquatic feed reduces the incidence of disease and enhances growth performance, although it presents harmful effects, such as development of resistant bacteria and accumulation in the natural environment. A variety of immune stimulants including probiotics, prebiotics, synbiotics, phytobiotics, organic acids, nucleotides, antioxidants, microalgae, yeast and enzymes have been used in the aquaculture industry. In recent decades, much attention has been paid on finding a variety of immunostimulants with lower cost which also affect specific and non-specific immunity and improve fish resistance against a wide range of pathogens. These stimulants strengthen the fish’s immune system by increasing the number of phagocytes, lysozyme activity and level of immunoglobulin. The use of immune stimulants as an effective tool to overcome diseases and strengthen the immune system of farmed species, leads to the promotion of cellular and humoral defense mechanisms and increases resistance to infectious diseases. Among these immunostimulants used in aquaculture, β-glucans are of particular importance. Glucans are complex polysaccharide compounds extracted from the cell wall of yeasts and fungi. These compounds can stimulate fish growth, survival, and immune function. Therefore, this review discusses the role and importance of β-glucan as a food additive in aquaculture and examines the impact of these compounds on the growth performance, immunity and biochemical parameters of farmed species.

Synbiotic combination of prebiotic, cacao pod husk pectin and probiotic, Lactobacillus plantarum, improve the immunocompetence and growth of Litopenaeus vannamei

To reach the sustainable development goals on waste recycling, cacao pod husk (CPH), produced as an agricultural waste byproduct during the cacao bean processing was applied to manufacture CPH pectin for developing the potential for diverse application in aquaculture, minimizing CPH impact to the environment and bringing benefits to the agriculture and aquaculture industries. In this study, CPH pectin (5 g/kg diet) and Lactobacillus plantarum (LP; 10¹⁰ cfu/kg diet) were separately introduced to the diets of Litopenaeus vannamei for a 56-day feeding trial, and two synbiotic combinations of CPH pectin and LP (CPH pectin at 5 g/kg diet + LP at 10⁷ cfu/kg diet or at 10¹⁰ cfu/kg diet) were also conducted. After the 56-day feeding trial, significantly elevated percent weight gain, percent length gains and feeding efficiency in L. vannamei were only observed in synbiotic combination of CPH pectin at 5 g/kg diet and LP at 10⁷ cfu/kg diet treatment, and the remainder of the treatments remained consistently similar to the control. Significantly increases in total haemocyte count, granular cells, phenoloxidase activity, and respiratory bursts were observed in L. vannamei fed with synbiotics at 7-28 days of feeding, accompanied by significant promotion of phagocytic activity and clearance efficiency in response to V. alginolyticus challenge during 56 days of feeding trial. Furthermore, at the end of the 56 days of feeding trial, shrimp receiving CPH pectin and/or LP treatments showed a significantly higher survival ratio against V. alginolyticus infection and hypothermal stress. It was therefore concluded that CPH pectin or LP was confirmed as an immunostimulant for L. vannamei to trigger immunocompetence through oral administration without negative effects within 56 days of feeding trial, and the synbiotic combination of CPH pectin and LP exhibited complementary and synergistic effects on growth performance and immunocompetence in L. vannamei.

Early Changes in Crayfish Hemocyte Proteins after Injection with a β-1,3-glucan, Compared to Saline Injected and Naive Animals

Early changes in hemocyte proteins in freshwater crayfish Pacifastacus leniusculus, in response to an injection with the fungal pattern recognition protein β-1,3-glucan (laminarin) were investigated, as well as changes after saline (vehicle) injection and in naïve animals. Injection of saline resulted in rapid recruitment of granular hemocytes from surrounding tissues, whereas laminarin injection on the other hand induced an initial dramatic drop of hemocytes. At six hours after injection, the hemocyte populations therefore were of different composition. The results show that mature granular hemocytes increase in number after saline injection as indicated by the high abundance of proteins present in granular cell vesicles, such as a vitelline membrane outer layer protein 1 homolog, mannose-binding lectin, masquerade, crustin 1 and serine protease homolog 1. After injection with the β-1,3-glucan, only three proteins were enhanced in expression, in comparison with saline-injected animals and uninjected controls. All of them may be associated with immune responses, such as a new and previously undescribed Kazal proteinase inhibitor. One interesting observation was that the clotting protein was increased dramatically in most of the animals injected with laminarin. The number of significantly affected proteins was very few after a laminarin injection when compared to uninjected and saline-injected crayfish. This finding may demonstrate some problematic issues with gene and protein expression studies from other crustaceans receiving injections with pathogens or pattern recognition proteins. If no uninjected controls are included and no information about hemocyte count (total or differential) is given, expressions data for proteins or mRNAs are very difficult to properly interpret.

Differentially Expressed Genes in Hepatopancreas of Acute Hepatopancreatic Necrosis Disease Tolerant and Susceptible Shrimp (Penaeus vannamei)

Acute hepatopancreatic necrosis disease (AHPND) is a lethal disease in marine shrimp that has caused large-scale mortalities in shrimp aquaculture in Asia and the Americas. The etiologic agent is a pathogenic Vibrio sp. carrying binary toxin genes, pirA and pirB in plasmid DNA. Developing AHPND tolerant shrimp lines is one of the prophylactic approaches to combat this disease. A selected genetic line of Penaeus vannamei was found to be tolerant to AHPND during screening for disease resistance. The mRNA expression of twelve immune and metabolic genes known to be involved in bacterial pathogenesis were measured by quantitative RT-PCR in two populations of shrimp, namely P1 that showed susceptibility to AHPND, and P2 that showed tolerance to AHPND. Among these genes, the mRNA expression of chymotrypsin A (ChyA) and serine protease (SP), genes that are involved in metabolism, and crustin-P (CRSTP) and prophenol oxidase activation system 2 (PPAE2), genes involved in bacterial pathogenesis in shrimp, showed differential expression between the two populations. The differential expression of these genes shed light on the mechanism of tolerance against AHPND and these genes can potentially serve as candidate markers for tolerance/susceptibility to AHPND in P. vannamei. This is the first report of a comparison of the mRNA expression profiles of AHPND tolerant and susceptible lines of P. vannamei.

Pectin of cacao pod husk, an efficient immunostimulant for white shrimp, Litopenaeus vannamei

The disposal of cacao pod husk, a byproduct of cacao bean processing, can cause serious adverse environmental impacts, motivating scientist to explore and develop potential beneficial applications of this resource. Dried cacao pod husk was extracted with ethanol to obtain a 10.6% pectin of cacao pod husks (pCPH), and its effects on the immunocompetence of Litopenaeus vannamei were estimated. Measured variables included total haemocyte count, differential haemocyte count, phenoloxidase activity, respiratory bursts, as well as phagocytic activity and clearance efficiency against Vibrio alginolyticus after receiving pCPH at 0, 1.5, 3, and 6 μg shrimp^-1 for 0, 1, 3 and 7 days via injection, and their resistance to thermal stress and V. alginolyticus infection were further evaluated. No significant differences were observed in total haemocyte count, differential haemocyte count, and respiratory bursts in shrimp receiving pCPH at 1.5 μg shrimp^-1 for 1 day; however, these variables were significantly elevated after 3 days of injection, compared to the control group. The significantly increased phenoloxidase activity was assessed in shrimp receiving pCPH at 1.5, 3 and 6 μg shrimp^-1 within 3 days, and activity returned to the baseline after 7 days. Furthermore, the reduced phenoloxidase activity per granulocytes or respiratory bursts per haemocytes maintained homeostasis following the variation of haemogram. For gene expression assessments in haemocytes, the immune-related genes of the lipopolysaccharide and β-1,3-glucan binding protein, prophenoloxidase II and anti-lipopolysaccharide factor as well as innate immune signaling pathway-related genes of toll-like receptors 1 and 3 significantly increased after shrimp received pCPH for 1 day. The increases in phagocytic activity and clearance efficiency were only detected in shrimp receiving pCPH at 6 μg shrimp^-1 within 7 days, compared to the control. There was no significant difference in the mortality ratio of shrimp against hyperthermal stress when they received pCPH for 1 day, and the significant higher resistance to hypothermal stress and V. alginolyticus infection were found in shrimp received pCPH at 6 μg shrimp^-1 for 1 days than those in the other treatments. It is therefore found that pCPH triggers immune responses serving as an immunostimulant capable of enhancing resistance against V. alginolyticus and hypothermal stress.

Role of novel protein kinase C in neuroendocrine-immune regulatory network in haemocytes of Litopenaeus vannamei: An in vitro approach

Shrimp lack adaptive immune systems and mainly rely on the cellular and humoral defences, involving the haemocytes (functionally analogous to vertebrate leukocytes) in non-self matter recognition, elimination, and in downstream coagulation. Furthermore, the linkage between stress-induced catecholamine (CA), a class of biogenic amines (BAs), releasing and immunological responses has been detected in shrimp. Varied isotypes of protein kinase C (PKC) regulate multiple cellular processes following their specific location and distribution within the cells, and a novel PKC identified in Litopenaeus vannamei (termed as LvnPKC) is proposed to mediate signaling transduction of immunocompetence and BA biosynthesis. In the present study, we analyzed the effects of the LvnPKC-silenced haemocytes by co-incubating with its dsRNA on the immune responses specific to prophenoloxidase (proPO) and antioxidant systems as well as phagocytic activity. In addition, the capability of haemocytes to produce BAs was assessed. The results revealed that LvnPKC-silenced haemocytes can induce interference in phenoloxidase and superoxide dismutase activities, respiratory bursts, and phagocytic activity; meanwhile, the disturbed gene expressions of proPO activating enzyme, proPOII, lipopolysaccharide- and β-1,3-glucan-binding protein, and cytosolic manganese superoxide dismutase were detected. The same deviated pattern was observed in tyrosine, dopamine, and norepinephrine levels, and in dopamine β-hydroxylase (DBH) activity and gene expressions of tyrosine hydroxylase, DOPA decarboxylase, and DBH involving in BA biosynthesis. Taken together, these results suggest that the immunocompetence and BA biosynthesis of haemocytes can be mediated via LvPKC signaling transduction, which proved the presence of a neuroendocrine-immune regulatory network in haemocytes.

An ShK-domain serine protease of Eriocheir sinensis regulates the PO activity to resist Spiroplasma eriocheiris infection

A novel serine protease contains two ShK-domain was found from the Chinese mitten crab Eriocheir sinensis (EsShK-SP). The full-length EsShK-SP cDNA is 1927 bp and contains a 1260-bp open reading frame encoding a protein of 420 amino acids, including a signal peptide, two ShK domain, and Tryp-SPC domain. Quantitative real-time PCR showed that EsShK-SP was expressed mainly in the hemocytes, gills, intestine, and nerve, but weakly in heart, muscle, and hepatopancreas. After infected with Spiroplasma eriocheiris, the expression of EsShK-SP was significantly up-regulated from 1 d to 9 d. The Tryp-SPC domain was ligated with pGEX-4T-1 vector and prokaryotic expressed to obtain recombinant protein rSPC. When rSPC and S. eriocheiris stimulated the hemocytes of E. sinensis, the PO activity was significantly up-regulated. The subcellular localization revealed that recombinant EsShK-SP was mainly located in the cytoplasm of Drosophila S2 cells. Both absolute real-time PCR and confocal laser scanning microscope results showed that over-expression of EsShK-SP in S2 cells could decrease the copy number of S. eriocheiris. Meanwhile, the over-expression of EsShK-SP also increased the PO activity and cell viability of S2 cells. After EsShK-SP RNA interference using dsRNA, the expression levels of proPO and activity of PO decreased significantly from 48 h to 96 h. The knockdown of EsShK-SP by RNAi resulted in the copy number of S. eriocheiris in the EsShK-SP silenced group was significantly increased compared to the control groups during S. eriocheiris infection. Meanwhile, the survival rate of crabs decreased in the EsShK-SP-dsRNA group. The above results indicated that EsShK-SP plays an important immune role during E. sinensis against S. eriocheiris through regulation of the proPO system.

Identification and functional characterization of a novel C-type lectin from the kuruma shrimp, Marsupenaeus japonicus

C-type lectins (CTLs) are immune molecules that are crucial to the invertebrate innate immune system with the primary function of recognizing invading pathogens. In the present study, a novel CTL was cloned from Marsupenaeus japonicus (MjCTL), and its tissue distribution and expression patterns over time in response to white spot syndrome virus (WSSV) and Vibrio parahaemolyticus were further investigated. The open reading frame (ORF) of MjCTL was 513 bp and encoded a polypeptide of 170 amino acids, which contained a signal peptide and a carbohydrate recognition domain (CRD) that are typical for CTLs. MjCTL was primarily expressed in the hepatopancreas and weakly expressed in hemocytes, gill, stomach, intestine, heart, muscle and eyestalk. The expression level of MjCTL in the hepatopancreas was dramatically increased at 48 h post-injection with WSSV at a dosage of 1 × 10⁵ virions. Glutathione-S-transferase (GST) pull-down assays showed that MjCTL could directly bind to several WSSV envelope proteins, including VP19, VP24, VP26 and VP28. Moreover, MjCTL displayed antibacterial activity against V. parahaemolyticus. Our results indicated that MjCTL exhibited multiple functions in innate immune response against pathogens.

Immune activation by a multigene family of lectins with variable tandem repeats in oriental river prawn (Macrobrachium nipponense)

Genomic regions with repeated sequences are unstable and prone to rapid DNA diversification. However, the role of tandem repeats within the coding region is not fully characterized. Here, we have identified a new hypervariable C-type lectin gene family with different numbers of tandem repeats (Rlecs; R means repeat) in oriental river prawn (Macrobrachium nipponense). Two types of repeat units (33 or 30 bp) are identified in the second exon, and the number of repeat units vary from 1 to 9. Rlecs can be classified into 15 types through phylogenetic analysis. The amino acid sequences in the same type of Rlec are highly conservative outside the repeat regions. The main differences among the Rlec types are evident in exon 5. A variable number of tandem repeats in Rlecs may be produced by slip mispairing during gene replication. Alternative splicing contributes to the multiplicity of forms in this lectin gene family, and different types of Rlecs vary in terms of tissue distribution, expression quantity and response to bacterial challenge. These variations suggest that Rlecs have functional diversity. The results of experiments on sugar binding, microbial inhibition and clearance, regulation of antimicrobial peptide gene expression and prophenoloxidase activation indicate that the function of Rlecs with the motif of YRSKDD in innate immunity is enhanced when the number of tandem repeats increases. Our results suggest that Rlecs undergo gene expansion through gene duplication and alternative splicing, which ultimately leads to functional diversity.

Injection of an extract of fresh cacao pod husks into Litopenaeus vannamei upregulates immune responses via innate immune signaling pathways

Immunostimulation is a novel method and a promising development in aquaculture. Products derived from plants exhibit various biological activities. In this study, the hot-water extract isolated from fresh cacao (Theobroma cacao) pod husks (CPHs) was administered by injection to evaluate cellular signaling pathways of innate immunity, the immunostimulating potential, disease resistance, and hypothermal tolerance of white shrimp, Litopenaeus vannamei. Results showed significant increases in the total hemocyte count, semigranular cells, granular cells, phenoloxidase activity, and respiratory bursts (RBs) of hemocytes per unit of hemolymph at 1 day, and in phagocytic activity toward and the clearance efficiency of Vibrio alginolyticus at 1-3 days after shrimp were injected with fresh CPH extract at 40 μg shrimp^-1. However, only RBs per hemocyte had significantly decreased at 1 day after the injection. All immune parameters had returned to control levels by 3 days after receiving fresh CPH extract except for RBs, phagocytic activity, and the clearance efficiency, which had returned to control values by 7 days. Furthermore, at 1 day after the injection, the peroxinectin, prophenoloxidase (proPO) II, toll-like receptors (TLR) 3, signal transducer and activator of transcription (STAT), and crustin in shrimp receiving fresh CPH extract at 20 μg shrimp^-1, and the lipopolysaccharide and β-1,3-glucan-binding protein, proPO II, TLR1, and STAT in shrimp receiving fresh CPH extract at 40 μg shrimp^-1 were significantly higher than those of shrimp receiving saline. After injecting fresh CPH extract at 10-40 μg shrimp^-1 and 40 μg shrimp^-1, the mortality of shrimp challenged with V. alginolyticus and exposed to 14 °C for 96 h significantly decreased, respectively. These results suggest that fresh CPH extract can be used as an immunostimulant and a physiological regulator for shrimp through injection administration to enhance immunological and physiological responses, which can elevate the resistance against V. alginolyticus and tolerance against hypothermal stress in L. vannamei.

The temporary modulation of tyramine on immune responses, carbohydrate metabolism, and catecholamines in Macrobrachium rosenbergii

Tyramine (TA), a biogenic monoamine, plays various important physiological roles including immunological regulation in invertebrates. In this study, the effects of TA on the regulation of immune resistance, carbohydrate metabolism and biogenic monoamine, as well as its signaling pathway in Macrobrachium rosenbergii were determined. Results showed that total haemocyte count, hyaline cells, semigranular cells, and phenoloxidase activity per 50 μL of haemolymph and per granulocyte (the sum of semigranular and granular cells) at 0.5 h as well as phagocytic activity and clearance efficiency to Lactococcus garvieae at 1 h of prawn injected with TA at 1 nmol prawn^-1 significantly increased, but the significantly decreased plasma lysozyme activity, phagocytic activity, clearance efficiency, and haemolymph glucose and dopamine were observed in prawn injected with TA at 10 nmol prawn^-1 for 0.5 h. Respiratory bursts and haemolymph lactate in two TA-injection treatments at 0.5 h and 0.5-1 h, respectively, were significantly higher than those of the saline control, and in addition, TA depressed dopamine release in a dose-dependent manner after 0.5 h of TA injection. All the examined parameters returned to control levels after prawn injected with TA for 2 h. The inhibited effect of TA (at 10 nmol prawn^-1 injection) on the phagocytic activity and clearance efficiency to pathogens was blocked by prazosin (an α1 adrenoceptors antagonist). For prawn received TA for 1 h then challenged with Lactococcus garvieae at 2 × 10⁵ colony-forming units prawn^-1, the survival ratio of TA 1 nmol prawn^-1-injected prawn significantly increased by 20%, compared to the saline-challenged control or TA 10 nmol prawn^-1-injected prawn after 144 h of challenge. These results suggested that the level of dopamine release suppression regulated by TA resulted in the immunoenhancing or immunosuppressive effects in prawn, and the signaling pathways of TA in mediating immune function were through octopamine (OA)/TA receptors.

Ciona robusta hemocyte populational dynamics and PO-dependent cytotoxic activity

Hemocyte populations from the ascidian Ciona robusta, separated through a Percoll discontinuous density gradient, are further characterized by May-Grünwald-Giemsa staining and a cytochemical reaction for phenoloxidase. Variability in cell density, acidophilic property and phenoloxidase activity suggest multiple hemocyte type populations, cell lineages and morphotypes that may be involved in distinct cellular responses. Therefore, unilocular refractile granulocytes, typical of this ascidian species, enriched in a fraction separated from the hemolymph show in vitro phenoloxidase-dependent cytotoxic activity against mammalian erythrocytes and a tumor cell lineage, in addition the properties listed above indicate relationships with vacuolated signet ring cells. Finally, bromo-deoxyuridine with, diamino-phenylindole fluorescent reaction and May-Grünwald-Giemsa staining show that in the hemolymph there are hyaline amoebocytes and granulocytes with potential proliferating activity. Present findings and reviewed images of previously reported inflammatory hemocytes in the tunic and pharynx allow us to speculate on theoretical outlines of hemocyte differentiation pathways.

Novel protein kinase C participates catecholamine biosynthesis and immunocompetence modulation in haemocytes of Litopenaeus vannamei

The catecholamine biosynthesis is required for physiological and immunological responses against stress, and the neuroendocrine-immune regulatory network plays a crucial role in immunocompetence of shrimp. A novel protein kinase C of Litopenaeus vannamei (LvnPKC) is involved in immune defense and signaling transduction in haemocytes, and in the present study, the gene silence technique is conducted to identify the role of LvnPKC on catecholamine biosynthesis and immunocompetence modulation in haemocytes of L. vannamei. The results show that tyrosine significantly increases in haemocytes of LvnPKC-silenced shrimp, and in the meantime, the obvious decrease of L-3, 4-dihydroxyphenylalanine and increase of dopamine as well as the consistent norepinephrine levels are detected. Tyrosine hydroxylase and dopamine β-hydroxylase activities are significantly reduced in haemocytes of LvnPKC-silenced shrimp. Total haemocyte count, hyaline cells and granulocytes insignificantly differ among treatments, and the obvious increase of phenoloxidase activity, respiratory bursts, superoxide dismutase and glutathione peroxidase activities are observed in haemocytes of LvnPKC-silenced shrimp, and furthermore, the downregulated phagocytic activity was observed. It is therefore concluded that the LvnPKC mediates catecholamine biosynthesis and immunocompetence in haemocytes, and plays a crucial role in the neuroendocrine-immune regulatory network.

Identification of two LGBPs (isoform1 and isoform2) and their function in AMP expression and PO activation in male hepatopancreas

Two lipopolysaccharides (LPS) and β-1, 3-glucan binding protein (LGBP), designated as PcLGBP isoform1 and PcLGBP isoform2, respectively, were identified from Procambarus clarkii in this study. The full-length cDNA of PcLGBP isoform1 was 1308 bp containing an open reading frame (ORF) of 1113 bp encoding a protein of 370 amino acids. The full-length cDNA of PcLGBP isoform2 was 1440 bp containing an ORF of 1245 bp encoding a protein of 414 amino acids. Predicted PcLGBP isoform1 and PcLGBP isoform 2 proteins contained a signal peptide, a glycoside hydrolase domain, and a low-complexity region. The difference between the two LGBP isoforms was that PcLGBP isoform2 had 44 more amino acids behind the signal peptide than the PcLGBP isoform1. The PcLGBP isoform1 and PcLGBP isoform2 transcripts mainly expressed in the hepatopancreas in female and male crayfish. Moreover, the expression levels of the two genes in the hepatopancreas were higher in male than that in female crayfish. Upon being challenged with Vibrio parahaemolyticus or LPS, the expression levels of PcLGBP isoform1 and PcLGBP isoform2 in the hepatopancreas of female and male crayfish were most significantly up-regulated at different time points. The transcripts of anti-lipopolysaccharide factors (ALF5, ALF6, ALF8, and ALF9) and crustins (CRU1, CRU2, CRU3, and CRU4) were evidently down-regulated in the hepatopancreas of V. parahaemolyticus-challenged total PcLGBP (including PcLGBP isoform1 and PcLGBP isoform2)-silenced male crayfish. In addition, the phenoloxidase (PO) activity in the hepatopancreas of male crayfish was evidently higher than that of female crayfish. PcLGBP knock down could significantly decrease the PO activity in the hepatopancreas lysate (HLS) in male crayfish. The PO activity of male crayfish HLS was significantly increased when incubated with a mixture of recombinant LGBP protein and LPS or β-1, 3 glucan. We conclude that LGBP isoforms from P. clarkii function as a pattern recognition protein for recognizing and binding LPS and β-1, 3 glucan, and thus regulate the synthesis of antimicrobial peptides and activate the prophenoloxidase system.

Phloroglucinol Treatment Induces Transgenerational Epigenetic Inherited Resistance Against Vibrio Infections and Thermal Stress in a Brine Shrimp (Artemia franciscana) Model

Emerging, infectious diseases in shrimp like acute hepatopancreatic necrosis disease (AHPND) caused by Vibrio parahaemolyticus and mortality caused by other Vibrio species such as Vibrio harveyi are worldwide related to huge economic losses in industrial shrimp production. As a strategy to prevent disease outbreaks, a plant-based phenolic compound could be used as a biocontrol agent. Here, using the brine shrimp (Artemia franciscana) as a model system, we showed that phloroglucinol treatment of the parental animals at early life stages resulted in transgenerational inherited increased resistance in their progeny against biotic stress, i.e., bacteria (V. parahaemolyticus AHPND strain and V. harveyi) and abiotic stress, i.e., lethal heat shock. Increased resistance was recorded in three subsequent generations. Innate immune-related gene expression profiles and potential epigenetic mechanisms were studied to discover the underlying protective mechanisms. Our results showed that phloroglucinol treatment of the brine shrimp parents significantly (P < 0.05) enhanced the expression of a core set of innate immune genes (DSCAM, proPO, PXN, HSP90, HSP70, and LGBP) in subsequent generations. We also demonstrated that epigenetic mechanisms such as DNA methylation, m6A RNA methylation, and histone acetylation and methylation (active chromatin marker i.e., H3K4Me3, H3K4me1, H3K27me1, H3 hyperacetylation, H3K14ac and repression marker, i.e., H3K27me3, H4 hypoacetylation) might play a role in regulation of gene expression leading toward the observed transgenerational inheritance of the resistant brine shrimp progenies. To our knowledge, this is the first report on transgenerational inheritance of a compound-induced robust protected phenotype in brine shrimp, particularly protected against AHPND caused by V. parahaemolyticus and vibriosis caused by V. harveyi. Results showed that epigenetic reprogramming is likely to play a role in the underlying mechanism.