Expression of DC-SIGN-like C-Type Lectin Receptors in Salmo salar

NLRC3 regulates RIP2, STING, TBK1, and TRAF6 mediated type I IFN signaling and inflammatory response in large yellow croaker Larimichthys crocea

As a member of the NLRs family, NLRC3 has been determined to function in the NF-κB, MAPK, and type I IFN signaling, which are crucial for the host innate immunity and inflammatory response. In this study, an NLRC3 ortholog, named as Lc-NLRC3, was cloned and identified in large yellow croaker (Larimichthys crocea). The gene characteristics analysis revealed that Lc-NLRC3 consists of 18 exons and 17 introns, with a full-length open reading frame (ORF) of 3405 bp, encoding a protein of 1134 amino acids (aa), that containing a N-terminal CARD domain, a central NACHT domain, and a C-terminal LRRs domain. It was shown that Lc-NLRC3 is predominantly found in the cytosol, and was widely distributed across various tissues/organs, with the highest expression detected in the intestine, and could be induced by poly I:C, LPS, PGN, and Pseudomonas plecoglossicida stimulation. Importantly, Lc-NLRC3 overexpression significantly activate NF-κB, TNFα, IL-1β, IRF3, IRF7, and IFN1 promoters, whereas when co-expressed with RIP2, STING, or TBK1, it down-regulated those promoter activation compared to their individual overexpression alone, thereby suppressing downstream antiviral and inflammatory gene expression. Interestingly, Lc-NLRC3 associated with TRAF6 in IRF3/IRF7 promoter activation, and enhanced the expression of IRF7, Mx, ISG15, and TNF-α. Co-immunoprecipitation assays also confirmed interactions of Lc-NLRC3 with RIP2, STING, TBK1, and TRAF6. The above results imply that Lc-NLRC3 is an important regulator in RIP2, STING, TBK1, and TRAF6 mediated type I IFN signaling and inflammatory response.

Transcriptionally distinct B cell profiles in systemic immune tissues and peritoneal cavity of Atlantic salmon (Salmo salar) infected with salmonid alphavirus subtype 3

Teleost B cells producing neutralizing antibodies contribute to protection against salmonid alphavirus (SAV) infection, the etiological agent of pancreas disease, thereby reducing mortality and disease severity. Our previous studies show differences in B cell responses between the systemic immune tissues (head kidney (HK) and spleen) and the peritoneal cavity (PerC) after intraperitoneal SAV3 infection in Atlantic salmon (Salmo salar) where the response in PerC dominates at the late time points. By employing the same infection model, we aimed to further characterize these B cells. Immunophenotyping of teleost B cells is challenging due to limited availability of markers; however, RNA-seq opens an opportunity to explore differences in transcriptomic responses of these cells. Our analysis identified 334, 259 and 613 differentially expressed genes (DEGs) in Atlantic salmon IgM+IgD+ B cells from HK, spleen, and PerC, respectively, at 6 weeks post SAV3 infection. Of these, only 34 were common to all the three immune sites. Additionally, out of the top 100 genes with the highest fold change in expression, only four genes were common across B cells from the three sites. Functional enrichment analyses of DEGs using KEGG and GO databases demonstrated differences in enriched innate immune signaling and the cytokine-cytokine interaction pathways in B cells across the sites, with varying numbers of genes involved. Overall, these findings show the presence of transcriptionally distinct B cell subsets with innate immune functions in HK, spleen and PerC of SAV3-infected Atlantic salmon. Further, our data provide new insights into the immunoregulatory role of fish B cells through the differential expression of various cytokine ligands and receptors and will be a useful resource for further studies into B cell immune compartments.

DC-SIGN of Largemouth Bass (Micropterus salmoides) Mediates Immune Functions against Aeromonas hydrophila through Collaboration with the TLR Signaling Pathway

C-type lectins in organisms play an important role in the process of innate immunity. In this study, a C-type lectin belonging to the DC-SIGN class of Micropterus salmoides was identified. MsDC-SIGN is classified as a type II transmembrane protein. The extracellular segment of MsDC-SIGN possesses a coiled-coil region and a carbohydrate recognition domain (CRD). The key amino acid motifs of the extracellular CRD of MsDC-SIGN in Ca2+-binding site 2 were EPN (Glu-Pro-Asn) and WYD (Trp-Tyr-Asp). MsDC-SIGN-CRD can bind to four pathogen-associated molecular patterns (PAMPs), including lipopolysaccharide (LPS), glucan, peptidoglycan (PGN), and mannan. Moreover, it can also bind to Gram-positive, Gram-negative bacteria, and fungi. Its CRD can agglutinate microbes and displays D-mannose and D-galactose binding specificity. MsDC-SIGN was distributed in seven tissues of the largemouth bass, among which the highest expression was observed in the liver, followed by the spleen and intestine. Additionally, MsDC-SIGN was present on the membrane of M. salmoides leukocytes, thereby augmenting the phagocytic activity against bacteria. In a subsequent investigation, the expression patterns of the MsDC-SIGN gene and key genes associated with the TLR signaling pathway (TLR4, NF-κB, and IL10) exhibited an up-regulated expression response to the stimulation of Aeromonas hydrophila. Furthermore, through RNA interference of MsDC-SIGN, the expression level of the DC-SIGN signaling pathway-related gene (RAF1) and key genes associated with the TLR signaling pathway (TLR4, NF-κB, and IL10) was decreased. Therefore, MsDC-SIGN plays a pivotal role in the immune defense against A. hydrophila by modulating the TLR signaling pathway.

Influence of host genetic polymorphisms involved in immune response and their role in the development of Chikungunya disease: a review

Chikungunya virus (CHIKV) is transmitted by the bite of infected mosquitoes and can cause significant pathogenicity in humans. Moreover, its importance has increased in the Americas since 2013. The primary vectors for viral delivery are the mosquito species Aedes aegypti and Aedes albopictus. Several factors, including host genetic variations and immune response against CHIKV, influence the outcomes of Chikungunya disease. This work aimed to gather information about different single nucleotide polymorphisms (SNPs) in genes that influence the host immune response during an infection by CHIKV. The viral characteristics, disease epidemiology, clinical manifestations, and immune response against CHIKV are also addressed. The main immune molecules related to this arboviral disease elucidated in this review are TLR3/7/8, DC-SIGN, HLA-DRB1/HLA-DQB1, TNF, IL1RN, OAS2/3, and CRP. Advances in knowledge about the genetic basis of the immune response during CHIKV infection are essential for expanding the understanding of disease pathophysiology, providing new genetic markers for prognosis, and identifying molecular targets for the development of new drug treatments.

Research Progress of Dendritic Cell Surface Receptors and Targeting

Dendritic cells are the only antigen-presenting cells capable of activating naive T cells in humans and mammals and are the most effective antigen-presenting cells. With deepening research, it has been found that dendritic cells have many subsets, and the surface receptors of each subset are different. Specific receptors targeting different subsets of DCs will cause different immune responses. At present, DC-targeted research plays an important role in the treatment and prevention of dozens of related diseases in the clinic. This article focuses on the current status of DC surface receptors and targeted applications.

Immune response of DNA vaccinated-gilthead seabream (Sparus aurata) against LCDV-Sa infection: relevance of the inflammatory process

Lymphocystis disease is one of the main viral pathologies affecting cultured gilthead seabream (Sparus aurata) in the Mediterranean region. Recently, we have developed a DNA vaccine based on the major capsid protein (MCP) of the Lymphocystis disease virus 3 (LCDV-Sa). The immune response triggered by either LCDV-Sa infection or vaccination have been previously studied and seem to be highly related to the modulation of the inflammatory and the IFN response. However, a comprehensive evaluation of immune-related gene expression in vaccinated fish after viral infection to identify immunogenes involved in vaccine-induced protection have not been carried out to date. The present study aimed to fulfill this objective by analyzing samples of head-kidney, spleen, intestine, and caudal fin from fish using an OpenArray® platform containing targets related to the immune response of gilthead seabream. The results obtained showed an increase of deregulated genes in the hematopoietic organs between vaccinated and non-vaccinated fish. However, in the intestine and fin, the results showed the opposite trend. The global effect of fish vaccination was a significant decrease (p<0.05) of viral replication in groups of fish previously vaccinated, and the expression of the following immune genes related to viral recognition (tlr9), humoral and cellular response (rag1 and cd48), inflammation (csf1r, elam, il1β, and il6), antiviral response (isg15, mx1, mx2, mx3), cell-mediated cytotoxicity (nccrp1), and apoptosis (prf1). The exclusive modulation of the immune response provoked by the vaccination seems to control the progression of the infection in the experimentally challenged gilthead seabream.

Molecular characterization and functional analysis of CD209E from Nile Tilapia (Oreochromis Niloticus) involved in immune response to bacterial infection

CD209 plays significant roles in pathogen recognition, innate and adaptive immunity, and cell-cell interactions. In the present study, a CD209 antigen-like protein E from Nile tilapia (Oreochromis niloticus) (designated as OnCD209E) was identified and characterized. OnCD209E contains an open reading frame (ORF) of 771 bp encoding a 257 amino acid protein, as well as the carbohydrate recognition domain (CRD). Multiple sequence analysis exhibits that the amino acid sequence of OnCD209E was relatively high homologous to that of partial fish, especially the highly conserved CRD, in which four conserved disulfide-bonded cysteine residues, WIGL conserved motif and two Ca²⁺/carbohydrate-binding sites (EPD and WFD motifs) were founded. Quantitative real-time PCR and Western Blot revealed that OnCD209E mRNA/protein is generally expressed in all tissues examined, but with wealth in head kidney and spleen tissues. The mRNA expression of OnCD209E was significantly increased in brain, head kidney, intestine, liver, and spleen tissues in response to the stimulation with polyinosinic-polycytidylic acid, Streptococcus agalactiae and Aeromonas hydrophila in vitro. Recombinant OnCD209E protein exhibited detectable bacterial binding and agglutination activity against different bacteria as well as inhibited the proliferation of tested bacteria. Subcellular localization analysis revealed that OnCD209E was mostly localized in the cell membrane. Moreover, overexpression of OnCD209E could activate nuclear factor-kappa B reporter genes in HEK-293T cells. Collectively, these results demonstrated that CD209E may potentially involve in immune response of Nile tilapia against bacterial infection.

Multiomic Approach for Bioprospection: Investigation of Toxins and Peptides of Brazilian Sea Anemone Bunodosoma caissarum

Sea anemones are sessile invertebrates of the phylum Cnidaria and their survival and evolutive success are highly related to the ability to produce and quickly inoculate venom, with the presence of potent toxins. In this study, a multi-omics approach was applied to characterize the protein composition of the tentacles and mucus of Bunodosoma caissarum, a species of sea anemone from the Brazilian coast. The tentacles transcriptome resulted in 23,444 annotated genes, of which 1% showed similarity with toxins or proteins related to toxin activity. In the proteome analysis, 430 polypeptides were consistently identified: 316 of them were more abundant in the tentacles while 114 were enriched in the mucus. Tentacle proteins were mostly enzymes, followed by DNA- and RNA-associated proteins, while in the mucus most proteins were toxins. In addition, peptidomics allowed the identification of large and small fragments of mature toxins, neuropeptides, and intracellular peptides. In conclusion, integrated omics identified previously unknown or uncharacterized genes in addition to 23 toxin-like proteins of therapeutic potential, improving the understanding of tentacle and mucus composition of sea anemones.

Identification, expression patterns, evolutionary characteristics and recombinant protein activities analysis of CD209 gene from Megalobrama amblycephala

CD209 is a type II transmembrane protein in the C-type lectin family, which is involved in the regulation of innate and adaptive immune system. Although it has been widely studied in mammals, but little has been reported about fish CD209 genes. In the present study, Megalobrama amblycephala CD209 (MaCD209) gene was cloned and characterized, its expression patterns, evolutionary characteristics, agglutinative and bacteriostatic activities were analyzed. These results showed that the open reading frame (ORF) of MaCD209 gene was 795 bp, encoding 264 aa, and the calculated molecular weight of the encoded protein was 29.7 kDa. MaCD209 was predicted to contain 2 N-glycosylation sites, 1 functional domain (C-LECT-DC-SIGN-like) and 1 transmembrane domain. Multiple sequence alignment showed that the amino acid sequence of MaCD209 was highly homologous with that of partial fishes, especially the highly conserved C-LECT-DC-SIGN-like domain and functional sites of CD209. Phylogenetic analysis showed that the CD209 genes from M. amblycephala and other cypriniformes fishes were clustered into one group, which was reliable and could be used for evolutionary analysis. Then, adaptive evolutionary analysis of teleost CD209 was conducted, and several positively selected sites were identified using site and branch-site models. Quantitative real-time PCR analysis showed that MaCD209 gene was highly expressed in the liver and heart. Moreover, the expression of MaCD209 was significantly induced upon Aeromonas hydrophila infection, with the peak levels at 4 h or 12 h post infection. The immunohistochemical analysis also revealed increased distribution of MaCD209 protein post bacterial infection. In addition, recombinant MaCD209 (rMaCD209) protein was prepared using a pET32a expression system, which showed excellent bacterial binding and agglutinative activities in a Ca²⁺-independent manner. However, rMaCD209 could only inhibit the proliferation of Escherichia coli rather than A. hydrophila. In conclusion, this study identified the MaCD209 gene, detected its expression and evolutionary characteristics, and evaluated the biological activities of rMaCD209 protein, which would provide a theoretical basis for understanding the evolution and functions of fish CD209 genes.

An Update of Lectins from Marine Organisms: Characterization, Extraction Methodology, and Potential Biofunctional Applications

Lectins are a unique group of nonimmune carbohydrate-binding proteins or glycoproteins that exhibit specific and reversible carbohydrate-binding activity in a non-catalytic manner. Lectins have diverse sources and are classified according to their origins, such as plant lectins, animal lectins, and fish lectins. Marine organisms including fish, crustaceans, and mollusks produce a myriad of lectins, including rhamnose binding lectins (RBL), fucose-binding lectins (FTL), mannose-binding lectin, galectins, galactose binding lectins, and C-type lectins. The widely used method of extracting lectins from marine samples is a simple two-step process employing a polar salt solution and purification by column chromatography. Lectins exert several immunomodulatory functions, including pathogen recognition, inflammatory reactions, participating in various hemocyte functions (e.g., agglutination), phagocytic reactions, among others. Lectins can also control cell proliferation, protein folding, RNA splicing, and trafficking of molecules. Due to their reported biological and pharmaceutical activities, lectins have attracted the attention of scientists and industries (i.e., food, biomedical, and pharmaceutical industries). Therefore, this review aims to update current information on lectins from marine organisms, their characterization, extraction, and biofunctionalities.

Differential Transcriptomic Response of Rainbow Trout to Infection with Two Strains of IPNV

The IPN virus (IPNV) causes a highly contagious disease that affects farmed salmonids. IPNV isolates have been phylogenetically classified into seven genogroups, of which two are present in Chile, genogroups 1 and 5. This study aimed to compare the transcriptomic response of rainbow trout fry challenged with two Chilean isolates of IPNV, RTTX (genogroup 1), and ALKA (genogroup 5). Tissue samples from challenged individuals and controls were taken at 1, 7, and 20 days post-challenge and analyzed by RNA-Seq. The results revealed that infection with RTTX elicited a greater modulation of the trout transcriptome compared to ALKA infection, generating a greater number of highly differentially expressed genes in relation to the control fish. Gene Ontology enrichment indicated that functions related to the inflammatory and immune responses were modulated in fish challenged with both isolates throughout the trial, but with different regulation patterns. On day 1 post challenge, these functions were activated in those challenged with ALKA, but suppressed in RTTX-challenged fish. These results suggest that rainbow trout exhibit a differential transcriptomic response to infection with the two genetically distinct IPNV isolates, especially at early times post-infection.

A C-type lectin with a single CRD from Onychostoma macrolepis mediates immune recognition against bacterial challenge

C-type lectins (CTL) are a large group of pattern-recognition proteins and to play important roles in glycoprotein metabolism, multicellular integration, and immunity. Based on their overall domain structure, they can be classified as different groups that possess different physiological functions. A typical C-type lectin (named as OmLec1) was identified from the fish, Onychostoma macrolepis, an important cultured fish in China. Open reading frame of OmLec1 contains a 570 bp, encoding a protein of 189 amino acids that includes a signal peptide and a single carbohydrate-recognition domain. The phylogenetic analysis showed that OmLec1 could be grouped with C-type lectin from other fish. OmLec1 was expressed in all the tissues in our study, and the expression level was highest in liver. And its relative expression levels were significantly upregulated following infection with Aeromonas hydrophila. The recombinant OmLec1 protein (rOmLec1) could agglutinate some Gram-negative bacteria and Gram-positive bacteria in vitro in the presence of Ca²⁺, showing a typical Ca²⁺-dependent carbohydrate-binding protein. Furthermore, rOmLec1 purified from E. coli BL21 (DE3), strongly bound to LPS and PGN, as well as all tested bacteria in a Ca²⁺-dependent manner. These results indicate that OmLec1 plays a central role in the innate immune response and as a pattern recognition receptor that recognizes diverse pathogens among O. macrolepis.

Identification and characterization of a C-type lectin in turbot (Scophthalmus maximus) which functioning as a pattern recognition receptor that binds and agglutinates various bacteria

C-type lectins (CTLs) are important pathogen pattern recognition receptors that recognize carbohydrate structures. In present study, a C-type lectin domain family 4 member E-like gene from turbot, which tentatively named SmCLEC4E-like (SmCLEC4EL), was identified, and the expressional and functional analyses were performed. In our results, SmCLEC4EL showed conserved synteny with CLEC4E-like genes from several fish species in genome, and possessed a typical type II transmembrane CTL architecture: an N-terminal intracellular region, a transmembrane domain and a C-terminal extracellular region which contained a predicted carbohydrate recognition domain (CRD). In addition, SmCLEC4EL exhibited the highest expression level in spleen in healthy fish, and showed significantly induced expression in mucosal tissues, intestine and skin, under bacteria challenge. Finally, the recombinant SmCLEC4EL protein combined with LPS, PGN, LTA and five different kinds of bacteria in a dose-dependent manner, and agglutinated these bacteria strains in the presence of calcium. These findings collectively demonstrated that SmCLEC4EL, a calcium-dependent CTL, could function as a pattern recognition receptor in pathogen recognition and participate in host anti-bacteria immunity.