Development of an ELISA for quantification of the antimicrobial peptide piscidin 4 and its application to assess stress in fish

Optimization and validation of analytical affinity chromatography for the in-process monitoring and quantification of peptides containing a C-tag

Antimicrobial peptides and proteins (AMPs) are promising alternatives to conventional antibiotics for the treatment of infections caused by multidrug-resistant bacteria. The production of recombinant AMPs is facilitated by platform technologies such as the C-tag, a sequence of four C-terminal amino acids that allows immunoaffinity capture and purification. However, the detection and quantification of such products throughout the manufacturing process is a significant challenge. We therefore used a design of experiments approach to optimize a novel high-throughput analytical immunoaffinity chromatography method for the accurate quantification of AMPs containing a C-tag, resulting in minimal analyte carryover (98.8 ± 0.1 % product elution). We then validated the method in accordance with International Conference on Harmonisation guideline Q2(R2). Validation confirmed that the method achieves high specificity, linearity, accuracy, and precision. We implemented in-process control and quantification throughout the manufacturing process, from cell lysis to the final purified product. We found that the lysate and acidic samples (pH < 2) can lead to deviations. However, following sample pretreatment, C-tag quantification reduced the error to ≤ 4 %, which is potentially superior to current non-specific quantification methods such as UV absorbance and colorimetry. Implementing this method for in-process control and quantification throughout the manufacturing process achieves the reliable assessment of product quantity and quality. This method also offers improvements over the product-specific enzyme-linked immunosorbent assay currently used for C-tagged products because it has a higher precision, accuracy and throughput, with a measurement time of 2.5 min per sample. Our analytical affinity chromatography method is therefore a valuable tool for the quantification of AMPs as part of a novel platform technology approach for C-tagged products.

The Role of Antimicrobial Peptides (AMPs) in Aquaculture Farming

&nbsp;Antimicrobial peptides (AMPs) are the vital constituents that stimulate the innate immune defense system against pathogens and perform several biological activities, which provide the first defensive line against infectious diseases. Owing to their unique structure, they can be utilized as a therapeutic strategy for infectious diseases in fishes. Several kinds of AMPs are reported in fishes with broad-spectrum antimicrobial properties. Besides, the bacterial cells cannot develop resistance strains against these cationic compounds with low molecular weight. Thus, AMPs may be considered an alternative to antibiotics to prevent or control infectious diseases in aquaculture. It is essential to provide sufficient knowledge about the mode of action of AMPs against fish pathogenic agents and their future applications.&nbsp;

Structure and regulation of the NK-lysin (1-4) and NK-lysin like (a and b) antimicrobial genes in rainbow trout (Oncorhynchus mykiss)

Nk-lysin (Nkl), an antimicrobial peptide (AMP) product of natural killer cells and cytotoxic T cells in mammals, has recently been characterized in a number of finfish species. In this study, we identified six genes with sequence homology to Nkl and characterized their patterns of mRNA expression and abundances in rainbow trout (Oncorhynchus mykiss). The cDNA sequences for the six Nkls encoded precursor peptides of 128-133 aa in length, and mature peptides of 109-111 aa in length. Genomic DNA of the nkl1-4 genes consisted of five exons and four introns, whereas the nkl-like a & b genes consisted of four exons and three introns. Chromosomal locations of these peptides show that nkl1 was located on chromosome arm 25q, whereas the other five nkl genes were clustered on chromosome arm 19q. Phylogenetic analysis revealed a conserved structure of Nkls among the teleosts and further protein sequence analyses suggests that all six nkl genes fall within the Nkl sub-family of the Saposin family of proteins. Patterns of tissue-specific mRNA expression were asymmetric among the six trout Nkl homologues, with nkl1, nkl3, and nkl-like a & b occurring in immune competent organs such as spleen, gill, intestine and kidney, as well as pineal gland, brain and oocytes. However, nkl2 and nkl4, showed primary abundances in brain, pineal gland and oocyte tissues. Using mRNA sequencing, in whole-body pools of juvenile trout fry (1 g bw) exposed to Flavobacterium psychrophilum infection, we observed modest up-regulation (2-3 fold) of five (nkl 2-4 and nkl-like a & b) of the six nkl mRNAs over the five-day post-challenge time-course. However, no upregulation could be recorded in spleen tissue measured by qPCR in juvenile trout (270 g bw). Using mRNA sequencing again, mRNA abundances were determined in gill of juvenile trout (~57.7 g bw) exposed to various aquaculture stressors. The results indicated that all six nkls (nkl1-4 and nkl-like a and nkl-like b) were downregulated when exposed to high temperature, and that nkl1 was significantly downregulated following salinity challenge. Overall, these newly characterized AMPs may contribute to host innate immunity as they are modulated following pathogen challenge and by physiological stressors.

Fish-derived antimicrobial peptides: Activity of a chionodracine mutant against bacterial models and human bacterial pathogens

The increasing resistance to conventional antibiotics is an urgent problem that can be addressed by the discovery of new antimicrobial drugs such as antimicrobial peptides (AMPs). AMPs are components of innate immune system of eukaryotes and are not prone to the conventional mechanisms that are responsible of drug resistance. Fish are an important source of AMPs and, recently, we have isolated and characterized a new 22 amino acid residues peptide, the chionodracine (Cnd), from the Antarctic icefish Chionodraco hamatus. In this paper we focused on a new Cnd-derived mutant peptide, namely Cnd-m3a, designed to improve the selectivity against prokaryotic cells and the antimicrobial activity against human pathogens of the initial Cnd template. Cnd-m3a was used for immunization of rabbits, which gave rise to a polyclonal antibody able to detect the peptide. The interaction kinetic of Cnd-m3a with the Antarctic bacterium Psychrobacter sp. (TAD1) was imaged using a transmission electron microscopy (TEM) immunogold method. Initially the peptide was associated with the plasma membrane, but after 180 min of incubation, it was found in the cytoplasm interacting with a DNA target inside the bacterial cells. Using fluorescent probes we showed that the newly designed mutant can create pores in the outer membrane of the bacteria E. coli and Psychrobacter sp. (TAD1), confirming the results of TEM analysis. Moreover, in vitro assays demonstrated that Cnd-m3a is able to bind lipid vesicles of different compositions with a preference toward negatively charged ones, which mimics the prokaryotic cell. The Cnd-m3a peptide showed quite low hemolytic activity and weak cytotoxic effect against human primary and tumor cell lines, but high antimicrobial activity against selected Gram - human pathogens. These results highlighted the high potential of the Cnd-m3a peptide as a starting point for developing a new human therapeutic agent.

The antibacterial activity and mechanism analysis of piscidin 5 like from Larimichthys crocea

Chemical drugs, such as antibiotics, were still important materials to prevent and cure diseases of aquatic organisms. However, antibiotics abuse do not only make the effects little, but also cause other bad problems, such as bacterial resistance and drug residues. Therefore, seeking the effective substitutes of antibiotics was an approach needed to be explored. Antibacterial peptides (AMPs) attracted more and more attention in the recent years. The parasitism and secondary bacterial invasion caused by ectroparasite Cryptocaryon irritans was a disaster to almost all host fish, including Larimichthys crocea. Reports indicated many AMPs played a key role in the whole parasitic infection cycle. Piscidin 5 like was a member of piscidin family. In the study, the antibacterial activity and mechanisms of piscidin 5 like from L.coreca (Lc-P5L) were detected. Liquid growth inhibition results showed recombinant Lc-P5L (rLc-P5L) had broad antibacterial spectrum and strong bactericidal activity. The bactericidal activity functioned in dose- and time-dependent manners. SEM (scanning electron microscope) observed the relatively detailed bactericidal process, rLc-P5L treatment resulted in a mass of bacteria piling together, appearing plenty of strange filaments and covering on the bacteria. Besides, S.aureus overgrowed plenty of granules, formed holes on the membrane of a few cells, and contents poured out from the holes. At the same time, antibacterial mechanisms were explored. After direct incubation with bacteria, western blot detected the apparently positive signal of rLc-P5L on bacteria; secondly, the incubation first with LPS (lipopolysaccharide) or LTA (lipoteichoic acid) significantly affect the binding of rLc-P5L to bacteria again, which indicated rLc-P5L could bind to bacteria through interaction with some PAMPs (pathogen-associated molecular patterns). In addition, rLc-P5L could interact with bacterial genome DNA by dose- and time-dependent means. In summary, rLc-P5L binded to bacteria surface through targeting to some PAMPs to damage membrane, and entered into cells to interact with genome DNA to disturb normal metabolism when it reached to some certain time and concentration thresholds, which were likely to be its pathway to exert antibacterial activity.

Distribution of three isoforms of antimicrobial peptide, chrysophsin-1, -2 and -3, in the red sea bream, Pagrus (Chrysophrys) major

We report here a liquid chromatography/electrospray ionization-tandem mass spectrometry assay for the quantification of three isoforms of antimicrobial peptide (AMP), chrysophsin-1, -2 and -3, in the red sea bream, Pagrus (Chrysophrys) major. Chrysophsin-1 was mainly distributed in the pyloric caeca and gills, followed by intestine and stomach. Chrysophsin-2 was detected in the gills and stomach, but chrysophsin-3 was only in the gills. The present procedure is valuable as a general method for simultaneous determination of the level of multiple AMP isoforms in fish tissues, and the data give important information for understanding the significance of each AMP isoform in host defense.

Pike intestinal reaction to Acanthocephalus lucii (Acanthocephala): immunohistochemical and ultrastructural surveys

Background

The Northern pike, Esox lucius, is a large, long-lived, top-predator fish species and occupies a broad range of aquatic environments. This species is on its way to becoming an important model organism and has the potential to contribute new knowledge and a better understanding of ecology and evolutionary biology. Very few studies have been done on the intestinal pathology of pike infected with helminths. The present study details the first Italian record of adult Acanthocephalus lucii reported in the intestine of E. lucius.

Results

A total of 22 pike from Lake Piediluco (Central Italy) were examined, of which 16 (72.7%) were infected with A. lucii. The most affected areas of gastrointestinal tract were the medium and distal intestine. The intensity of infection ranged from 1 to 18 parasites per host. Acanthocephalus lucii penetrated mucosal and submucosal layers which had a high number of mast cells (MCs) with an intense degranulation. The cellular elements involved in the immune response within the intestine of pike were assessed by ultrastructural techniques and immunohistochemistry using antibodies against met-enkephalin, immunoglobulin E (IgE)-like receptor (FCεRIγ), histamine, interleukin-6, interleukin-1β, substance P, lysozyme, serotonin, inducible-nitric oxide synthase (i-NOS), tumor necrosis factor-α (TNF-α) and the antimicrobial peptide piscidin 3 (P3). In intestines of the pike, several MCs were immunopositive to 9 out of the 11 aforementioned antibodies and infected fish had a higher number of positive MCs when compared to uninfected fish.

Conclusions

Pike intestinal tissue response to A. lucii was documented. Numerous MCs were seen throughout the mucosa and submucosal layers. In infected and uninfected intestines of pike, MCs were the dominant immune cell type encountered; they are the most common granulocyte type involved in several fish-helminth systems. Immunopositivity of MCs to 9 out of 11 antibodies is of great interest and these cells could play an important key role in the host response to an enteric helminth. This is the first report of A. lucii in an Italian population of E. lucius and the first account on positivity of MCs to piscidin 3 and histamine in a non-perciform fish.

Effects of cortisol and lipopolysaccharide on expression of select growth-, stress- and immune-related genes in rainbow trout liver

Many studies have shown that stress-induced cortisol levels negatively influence growth and immunity in finfish. Despite this knowledge, few studies have assessed the direct effects of cortisol on liver immune function. Using real-time PCR, the expression of three cortisol-responsive genes (GR: glucocorticoid receptor, IGF-1: insulin-like growth factor-I and SOCS-1: suppressor of cytokine signaling-I), genes involved with innate and adaptive immunity (IL-1β: interleukin-1 beta, IgM: immunoglobin-M and Lyz: lysozyme), and liver-specific antimicrobial peptides (hepcidin and LEAP-2A: liver-expressed antimicrobial peptide-2A) was studied in vitro using rainbow trout liver slices. The abundances of GR, SOCS-1 and IGF-1 mRNAs were suppressed by cortisol treatment. Abundance of IL-1β mRNA was upregulated by LPS and suppressed by cortisol treatment in a time-dependent manner. While abundance of IgM mRNA was suppressed by cortisol treatment and stimulated by LPS, there were no effects of cortisol or LPS on abundance of Lyz mRNA. Abundance of hepcidin and LEAP-2A mRNA levels were suppressed by cortisol treatment and stimulated by LPS. These results demonstrate that cortisol directly suppresses abundance of GR, IGF-1, IL-1β, IgM, hepcidin, LEAP-2A and SOCS-1 mRNA transcripts in the rainbow trout liver. We report for the first time, a suppressive effect of cortisol (within 8 h of treatment) on hepcidin and LEAP-2A mRNAs in rainbow trout liver, which suggests that acute stress may negatively affect liver immune function in rainbow trout.

Fish antimicrobial peptides (AMP's) as essential and promising molecular therapeutic agents: A review

Antimicrobial peptides (AMPs) are generally considered as an essential component of innate immunity, thereby providing the first line of defense against wide range of pathogens. In addition, they can also kill the pathogens which are generally resistant to number of antibiotics, thereby providing the avenues for the development of future therapeutic agents. Fishes are constantly challenged by variety of pathogens which not only shows detrimental effect on their health but also increases risk of becoming resistant to conventional antibiotics. As fishes rely more on innate immunity, AMPs can serve as a potential defensive weapons in fishes for combating emerging devastating diseases. Generally, AMPs show multidimensional properties like rapid diffusion to the site of infection, recruitment of other immune cells to infected tissues and vigorous potential to rapidly neutralize broad range of pathogens (bacterial, fungal and viral). AMPs also exhibit diverse biological effect like endotoxin neutralization, immunomodulation and induction of angiogenesis in mammals. Due to these properties AMPs have become one of the most promising therapeutic agents to be studied. Till date, many AMPs have been isolated from the fishes but not fully characterized at molecular level. This review provides an overview of the structures, functions, and putative mechanisms of major families of fish AMPs. Further, we also highlighted how fish AMPs can be used as a novel therapeutic tool which is the theme of future research in drug development.

A fish model for the study of the relationship between neuroendocrine and immune cells in the intestinal epithelium: Silurus glanis infected with a tapeworm

Immunohistochemical, immunofluorescence and ultrastructural studies were conducted on a sub-population of 20 wels catfish Silurus glanis from a tributary of the River Po (Northern Italy). Fish were examined for the presence of ecto- and endo-parasites; in the intestine of 5 fish, 11 specimens of cestode Glanitaenia osculata were noted and was the only helminth species encountered. The architecture of intestine and its cellular features were nearly identical in either the uninfected S. glanis or in those harboring G. osculata. Near the site of worm's attachment, mucous cells, several mast cells (MCs), few neutrophils and some endocrine cells (ECs) were found to co-occur within the intestinal epithelium. MCs and neutrophils were abundant also in the submucosa. Immunohistochemical staining revealed that enteric ECs were immunoreactive to met-enkephalin, galanin and serotonin anti-bodies. The numbers of ECs, mucous cells and MCs were significantly higher in infected wels catfish (Mann-Whitney U test, p < 0.05). Dual immunofluorescence staining with the biotinylated lectin Sambucus nigra Agglutinin and the rabbit polyclonal anti-met-enkephalin or anti-serotonin, with parallel transmission electron microscopy, showed that ECs often made intimate contact with the mucous cells and epithelial MCs. The presence of numerous MCs in intestinal epithelium shows S. glanis to be an interesting model fish to study processes underlying intestinal inflammation elicited by an enteric worm. Immune cells, ECs and mucous cells of the intestinal epithelium have been described at the ultrastructural level and their possible functions and interactions together will be discussed.

A Diverse Family of Host-Defense Peptides (Piscidins) Exhibit Specialized Anti-Bacterial and Anti-Protozoal Activities in Fishes

Conventional antibiotics and other chemical-based drugs are currently one of the most common methods used to control disease-related mortality in animal agriculture. Use of the innate immune system to decrease disease related mortalities is a novel alternative to conventional drugs. One component of the innate immune system is the host-defense peptides, also known as antimicrobial peptides. Host-defense peptides are typically small, amphipathic, α-helical peptides with a broad-spectrum of action against viral, bacterial, fungal, and/or protozoal pathogens. Piscidins are host-defense peptides first discovered in the hybrid striped bass (white bass, Morone chrysops, x striped bass, M. saxatilis). In this paper we identify four new piscidin isoforms in the hybrid striped bass and describe their tissue distributions. We also determine the progenitor species of origin of each piscidin (orthology) and propose a revised nomenclature for this newly described piscidin family based on a three class system. The Class I piscidins (22 amino acids in length; striped bass and white bass piscidin 1 and piscidin 3) show broad-spectrum activity against bacteria and ciliated protozoans, while the Class III piscidins (55 amino acids in length; striped bass and white bass piscidin 6 and striped bass piscidin 7) primarily show anti-protozoal activity. The Class II piscidins (44-46 amino acids in length; striped bass and white bass piscidin 4 and white bass piscidin 5) have a level of activity against bacteria and protozoans intermediate to Classes I and III. Knowledge of piscidin function and activity may help in the future development of disease-resistant lines of striped bass and white bass that could be used to produce superior hybrids for aquaculture.

Piscidin: Antimicrobial peptide of rock bream, Oplegnathus fasciatus

The piscidin family consists of antimicrobial peptides (AMPs) that are mainly found in fish and are crucial effectors of fish innate immune responses. The piscidin family typically has broad-spectrum antimicrobial activity and can modulate immune responses. In this study, we cloned rock bream piscidin (Rbpisc) and investigated its gene expression and biological activity (including antimicrobial and cytotoxic activities). The coding region of Rbpisc consisted of 213 base pairs (bp) encoding 70 amino acid residues. The tertiary structure predicted for Rbpisc includes an amphipathic helix-loop-helix structure. The Rbpisc gene was highly expressed in the gills of healthy fish. The gene expression of Rbpisc increased in the gills after pathogen infection, while the expression was down-regulated in other tissues. A synthetic peptide based on the AMP 12 domain amino acid sequence of Rbpisc appeared to have broad-spectrum antimicrobial activity against various bacteria. However, the synthetic peptide exhibited weak haemolytic activity against fish erythrocytes. These results suggest that Rbpisc might play an important role in the innate immune responses of rock bream.

Pro-inflammatory caspase-1 activation during the immune response in cells from rainbow trout Oncorhynchus mykiss (Walbaum 1792) challenged with pathogen-associated molecular patterns

In response to pathogens, the higher vertebrate innate immune system activates pro-inflammatory caspase-1 which is responsible for the processing and secretion of several important cytokines involved in the host's defence against infection. To date, caspase-1 has been described in few teleost fish, and its activity has been demonstrated through substrate cleavage and inhibition by pharmacological agents. In this study, the detection of the active form of caspase-1 during the immune response in salmonid fish is described, where two antibodies were produced. These antibodies differentially recognize the structural epitopes of the inactive pro-caspase-1 and the processed active form of the caspase. Firstly, caspase-1 activation was demonstrated in vitro by ELISA, Western blotting and immunocytochemistry in rainbow trout macrophages exposed to different pathogen-associated molecular patterns plus the pathogen Aeromonas hydrophila. This activity was clearly abrogated by a caspase inhibitor and seems to be unrelated to IL-1β secretion. Caspase-1 activation was then validated in vivo in gill cells from fish challenged with Aeromonas salmonicida. These results represent the first demonstration of caspase-1 activation in salmonids, and the first evidence of the putative regulatory role which this protease plays in inflammatory response in this fish group, as described for some other teleosts and mammals.

Antimicrobial Peptides as Mediators of Innate Immunity in Teleosts

Antimicrobial peptides (AMPs) have been identified throughout the metazoa suggesting their evolutionarily conserved nature and their presence in teleosts is no exception. AMPs are short (18–46 amino acids), usually cationic, amphipathic peptides. While AMPs are diverse in amino acid sequence, with no two AMPs being identical, they collectively appear to have conserved functions in the innate immunity of animals towards the pathogens they encounter in their environment. Fish AMPs are upregulated in response to pathogens and appear to have direct broad-spectrum antimicrobial activity towards both human and fish pathogens. However, an emerging role for AMPs as immunomodulatory molecules has become apparent—the ability of AMPs to activate the innate immune system sheds light onto the multifaceted capacity of these small peptides to combat pathogens through direct and indirect means. Herein, this review focuses on the role of teleost AMPs as modulators of the innate immune system and their regulation in response to pathogens or other exogenous molecules. The capacity to regulate AMP expression by exogenous factors may prove useful in modulating AMP expression in fish to prevent disease, particularly in aquaculture settings where crowded conditions and environmental stress pre-dispose these fish to infection.

Immunogenicity and pharmacokinetics of short, proline-rich antimicrobial peptides

Aim: The potential of proline-rich antimicrobial peptides (PrAMPs) to treat multidrug-resistant Gram-negative pathogens has been intensively investigated. They are efficacious at low doses in infection models and well tolerated in healthy mice at high doses. Methods & results: PrAMPs Onc72 and Api88 were nonimmunogenic in mice unless conjugated to a carrier protein. Monoclonal IgG1/IgG2b antibodies produced by hybridoma cells were mapped to different Onc72 regions and combined in a sandwich-ELISA in a pharmacokinetic study. Onc72 was detected at concentrations up to 32 µg/ml in murine blood after administering 20 mg/kg and reached several organs within 10 min. Conclusion: Both PrAMPs were not immunogenic and Onc72 concentrations in blood were well above the minimal inhibitory concentrations for Enterobacteriaceae further confirming their potential as novel antibiotics.

Histopathology and the inflammatory response of European perch, Perca fluviatilis muscle infected with Eustrongylides sp. (Nematoda)

BACKGROUND

The European perch, Perca fluviatilis L. is a common paratenic host of dioctophymatid nematodes belonging to the genus Eustrongylides. In this host, once infected oligochaetes, which serve as the first intermediate host, are ingested, Eustrongylides migrates through the intestine and is frequently encountered within the musculature, free within the body cavity, or encapsulated on the viscera. The current study details the first Italian record of Eustrongylides sp. with larvae reported in the muscle of P. fluviatilis.

METHODS

Uninfected and nematode-infected muscle tissues of perch were fixed and prepared for histological evaluation and electron microscopy. Some sections were subjected to an indirect immunohistochemical method using anti-PCNA, anti-piscidin 3 and anti-piscidin 4 antibodies.

RESULTS

A total of 510 P. fluviatilis (TL range 15-25 cm) from Lake Trasimeno, Perugia were post-mortemed; 31 individuals had encysted nematode larvae within their musculature (1-2 worms fish(-1)). Histologically, larvae were surrounded by a capsule with an evident acute inflammatory reaction. Muscle degeneration and necrosis extending throughout the sarcoplasm, sarcolemmal basal lamina, endomysial connective tissue cells and capillaries was frequently observed. Within the encapsulating reaction, macrophage aggregates (MAs) were seen. Immunohistochemical staining with the proliferating cell nuclear antigen (PCNA) revealed numerous PCNA-positive cells within the thickness of the capsule and in the immediate vicinity surrounding Eustrongylides sp. larvae (i.e. fibroblasts and satellite cells), suggesting a host response had been initiated to repair the nematode-damaged muscle. Mast cells (MCs) staining positively for piscidin 3, were demonstrated for the first time in response to a muscle-infecting nematode. The piscidin 3 positive MC's were seen principally in the periphery of the capsule surrounding the Eustrongylides sp. larva.

CONCLUSIONS

A host tissue response to Eustrongylides sp. larvae infecting the musculature of P. fluviatilis was observed. Numerous fibroblasts, MAs and MCs were seen throughout the thick fibroconnectival layer of the capsule enclosing larvae. PCNA positive cells within the capsule suggest that host repair of nematode damaged muscle does occur, while the presence of the antimicrobial peptide piscidin 3 is shown for the first time. This is first report of Eustrongylides sp. in an Italian population of P. fluviatilis.

Measures of immune system status in young-of-the-year winter flounder Pseudopleuronectes americanus

The immune status of young-of-the-year (YOY) winter flounder Pseudopleuronectes americanus was evaluated in fish collected from six areas around Long Island, NY, U.S.A. representing more urban areas with high population density in the west, to less densely populated more rural areas in to the east. Gene expression markers for innate immunity (pleurocidin) and contaminant exposure (cytochrome P4501A; cyp1a) were measured in liver and fin of fish collected at each site. Expression of pleurocidin was significantly higher in fin than liver, but was highly variable among individuals. Some statistically significant differences in pleurocidin expression among sites were observed, although elevated levels were not associated with degree of urbanization. Expression was related in part to fish size: a positive correlation between expression and total length (LT ) of fish was observed with the largest LT class (>125 mm) exhibiting significantly elevated pleurocidin expression as compared with fish in the smaller LT class. This indicates that immune competency may increase with age. No site-specific differences in cyp1a expression were observed. These data suggest that exposure to aromatic hydrocarbon contaminants is fairly widespread throughout the study area and that any differences in pleurocidin expression in YOY P. americanus are probably due to other factors. Antimicrobial activity was also measured as a functional indicator of immune response. Activity was highly variable, showing no significant site-specific differences, and no significant correlation to pleurocidin expression. The lack of correlation between pleurocidin expression and antimicrobial activity indicates that other antimicrobial peptides may be active against the bacteria tested or that other factors are influencing antimicrobial activity. This is the first quantitative evaluation of pleurocidin expression in YOY P. americanus from an urban area. Further work is needed to characterize factors controlling pleurocidin expression, as well as other indicators of immune response in young fish.

Expression analysis and biological activity of moronecidin from rock bream, Oplegnathus fasciatus

The piscidin-family, one of antimicrobial peptides (AMPs) mainly distributed in fish, is crucial effectors of fish innate immune response. Piscidin-family typically has broad-spectrum antimicrobial activity and the ability to modulate the immune response. In this study, we identified moronecidin (Rbmoro) included in piscidin-family from rock bream and investigated its gene expression using quantitative real-time PCR and biological activity (including antimicrobial and cytotoxic activity). The coding region of Rbmoro was 204 bp encoding 67 amino acid residues. Tertiary structure prediction of Rbmoro showed an amphipathic α-helical structure. Rbmoro gene was widely expressed in different tissues of healthy fish. Additionally, Rbmoro gene expression was induced in all tested tissues after infection with Edwardsiella tarda, Streptococcus iniae and red seabream iridovirus. We synthesized mature peptide of Rbmoro based on amino acid sequence of its AMP 12 domain, and the synthetic peptide appeared broad-spectrum antimicrobial activity to various bacteria. However, the synthetic peptide has weak haemolytic activity against fish erythrocytes. These results suggest that Rbmoro might play an important role in innate immune response of rock bream.

Piscidins in the intestine of European perch, Perca fluviatilis, naturally infected with an enteric worm

This study set out to determine how an enteric parasite, the thorny-headed worm Acanthocephalus lucii, affected the expression of antimicrobial peptides (piscidins) in its host population, the European perch (Perca fluviatilis) collected from Lake Piediluco in Central Italy. A total of 87 perch were examined; 44 (50.5%) were infected with A. lucii (1-18 worms fish(-1)). Pathological changes and immune response were assessed using histological, ultrastructural and immunohistochemical techniques. The acanthocephalans only penetrated the surficial zone of the intestinal wall and induced only slight inflammation. The main damage was destruction of the mucosal epithelium covering the villi adjacent to the parasite's attachment site, and included necrosis and degeneration. Infected intestine had numerous mast cells (MCs), often in close proximity to, and within, the capillaries, and were associated with fibroblasts of the submucosal layer. Mast cells were irregular in shape with a cytoplasm filled by numerous electron-dense, membrane-bounded granules. Immunostaining of intestine with antibodies against the antimicrobial peptides piscidin 3 and piscidin 4 showed subpopulations of MCs that were positive. Piscidin-positive MCs were mainly observed among the epithelial cells of the intestine, but also within the submucosa. In both uninfected and parasite-infected perch, the number of MCs positive for piscidin 4 was higher than those immunoreactive with piscidin 3 (p < 0.05). For both piscidins, there was no significant difference in the number of positive MCs between parasite-infected and uninfected intestine (p > 0.05). However, uninfected fish showed higher immunostaining intensity for piscidin 3 than infected conspecifics (p < 0.05).

Development of a sandwich ELISA for quantifying hepcidin in Rainbow trout

One of the most widespread antimicrobial peptides (AMPs) in fish is the hepcidins, which have potent, broad-spectrum activity against viruses, bacteria, fungi, and parasites. Moreover, they play the role of central regulation of iron metabolism and their expression is over-regulated by bacterial and viral infections, inflammation and vaccination. Quantification of their expression is an important factor in understanding their function. We therefore generated two polyclonal antibodies using synthetic peptides in order to measure hepcidin expression via sandwich ELISA. The specificity of both antibodies was confirmed by identifying an absence of cross-reactivity with other peptides that have similar pI and with the detection by Western blot of only one 9.6 kDa immunoreactive band corresponding to the hepcidin prepropeptide. The sensitivity of the sandwich ELISA was in the order of 0.005 ng/μL of hepcidin, which allowed analysis of the presence of the peptide and its variation in different tissues of Oncorhynchus mykiss. With the sandwich ELISA it could be seen that hepcidin expression in rainbow trout challenged with Aeromonas salmonicida was increased twofold over the untreated fish in head kidney samples, in correlation with the increase in the observed transcriptional level in the head kidney cells. These results provide the first evidence for quantifying the presence of active hepcidin and may be a useful indicator of disease susceptibility, providing a new, sensitive tool for rapid screening of population health.

A complementary LC-ESI-MS and MALDI-TOF approach for screening antibacterial proteomic signature of farmed European sea bass mucus

Antibacterial protection in the mucus is provided by antimicrobial compounds and till now few numbers of AMP and proteins were identified. Herein, mass spectral profiling of fresh mucus from farmed sea bass (Dicentrarchus labrax) using Matrix-assisted laser desorption/ionization-time-of-flight mass spectrometer (MALDI-TOF) and liquid chromatography mass spectrometry is investigated in order to survey the infective/healthy status of the mucus. We identify AMP peptides of 2891.7, 2919.45 and 2286.6 Da molecular weight respectively and characterize Chrysophsins in the mucus of Dicentrarchus labrax. These peptides display broad-spectrum bactericidal activity against Gram-negative (Minimum Inhibitory Concentrations namely MICs < 0.5 μM) and Gram-positive bacteria (MICs < 0.5 μM) including Escherichia coli and Bacillus subtilis. Furthermore, sensitivity to yeast Candida albicans is reported for the first time and shows interesting MICs of less than 2 μM. We also demonstrate that the fish pathogen Aeromonas salmonoicida is sensitive to Chrysophsins (MICs ranging between 5 and 14 μM). Our mucus molecular mass mapping developed approach allows for fast exploration of immune status. Our data provides evidence that Chrysophsins are secreted by immune cells and are released in mucus of non-challenged farmed European sea bass. These results suggest that Chrysophsins, secreted by gills of red sea bream, are an important widespread component of Teleostei defense against disease.

Peptides as the next generation of anti-infectives

Synthesis and large-scale manufacturing technologies are now available for the commercial production of even the most complex peptide anti-infectives. Married with the potential of this class of molecule as the next generation of effective, resistance-free and safe antimicrobials, and a much better understanding of their biology, pharmacology and pharmacodynamics, the first regulatory approvals and introduction into clinical practice of these promising drug candidates will likely be soon. This is a key juncture in the history/life cycle of peptide anti-infectives and, perhaps, their commercial and therapeutic potential is about to be realized. This review highlights the promise of these agents as the next generation of therapeutics and summarizes the challenges faced in, and lessons learned from, the past.

A piscidin-like antimicrobial peptide from the icefish Chionodraco hamatus (Perciformes: Channichthyidae): molecular characterization, localization and bactericidal activity

Antimicrobial peptides (AMPs) are considered one of the most ancient components of the innate immune system. They are able to exert their protection activity against a variety of microorganisms, and are widely distributed in both vertebrates and invertebrates. In this paper we focused on an AMP identified in the Antarctic teleost Chionodraco hamatus, an icefish species. The cDNA sequence of the AMP, named chionodracine, is comprised of 515 bp and translates for a putative protein precursor of 80 amino acids, with a signal peptide of 22 amino acids. The structural features evidenced in the primary sequence of chionodracine lead to the inclusion of the peptide in the antimicrobial family of piscidins. The analysis by real-time PCR of the basal gene transcripts of chionodracine in different icefish tissues showed that the highest expression was found in gills, followed by head kidney. The chionodracine expression levels in head kidney leukocytes were up-regulated in vitro both by LPS and poly I:C, and in vivo by LPS. A putative chionodracine mature peptide was synthesized and employed to obtain a polyclonal antiserum, which was used in immunohistochemistry of gills sections and revealed a significant positivity associated with mast cells. The bactericidal activity of the peptide was investigated and found significant against Antarctic psychrophilic bacteria strains (Psychrobacter sp. TAD1 and TA144), the Gram-positive Bacillus cereus, and at a lesser extent against the Gram-negative Escherichia coli. Interestingly, the haemolytic activity of chionodracine was tested in vitro on human erythrocytes and no significant lysis occurred until peptide concentration of 50 μM.

Development of a new antibody for detecting natural killer enhancing factor (NKEF)-like protein in infected salmonids

The main cellular responses of innate immunity are phagocytic activity and the respiratory burst, which produces a high amount of reactive oxygen species. Natural killer enhancing factor (NKEF) belongs to the peroxiredoxin family that has an antioxidant function and enhances cytotoxic cell activity. This molecule may play a key role in macrophage and cytotoxic cell communication during the innate immune response of fish against pathogens. In fish, the NKEF gene has been characterized in some species as showing an up-regulation in infected fish, suggesting a trigger effect upon NK-like cells. To detect and localize this molecule in salmonids at protein level, a monospecific polyclonal antibody was generated. A probable NKEF-like protein epitope region was identified and characterized using bioinformatic tools, and the sequence was chemically synthesized using Fmoc strategy, analysed by RP-HPLC and its molecular weight confirmed by mass spectrometry. The synthetic peptide was immunized and antibodies from ascitic fluid were obtained. The resulting antibody is a versatile tool for detecting NKEF by different immune techniques such as ELISA, Western blotting and immunohistochemistry. Analysis of NKEF-like protein is a useful method for characterizing immune properties of this molecule in fish during response to pathogens.

Impact of acute stress on antimicrobial polypeptides mRNA copy number in several tissues of marine sea bass (Dicentrarchus labrax)

Background

In comparison to higher vertebrates, fish are thought to rely heavily on innate immune system for initial protection against pathogen invasion because their acquired immune system displays a considerably poor immunological memory, and short-lived secondary response. The endogenous antimicrobial polypeptides (AMPPs) directly and rapidly killing pathogens such as bacteria, fungi, parasites, and viruses are included within the realm of innate defenses. In addition to piscidins, AMPPs that in recent years have been shown to be commonly linked to innate defense, are histones and their polypeptide fragments, and peptides derived from the respiratory protein hemoglobin. There is evidence that a number of stresses lead to significant regulation of AMPPs and thus their monitoring could be a highly sensitive measure of health status and risk of an infectious disease outbreak, which is a major impediment to the continued success of virtually all aquaculture enterprises and is often the most significant cause of economic losses.

Results

We firstly isolated and deposited in Genbank database the cDNA sequences encoding for hemoglobin-β-like protein (Hb-LP) [GeneBank: JN410659], H2B histone-like protein 1 (HLP1) GenBank: JN410660], and HLP2 [GenBank: JN410661]. The "de novo" prediction of the three-dimensional structures for each protein is presented. Phylogenetic trees were constructed on Hb-LP, HLP1, and HLP2 sequences of sea bass and those of other teleost, avian, reptiles, amphibian and mammalian species. We then used real time RT-PCR technology to monitor for the first time in sea bass, dynamic changes in mRNA copy number of Hb-LP, HLP1, HLP2, and dicentracin in gills, skin, eyes, stomach and proximal intestine in response to acute crowding/confinement stress. We showed that acute crowding stress induces an increase in the expression levels of the aforementioned genes, in gills and skin of sea bass, but not in other tissues, and that this expression patterns are not always rapidly reversed upon re-exposure to normal conditions.

Conclusion

The higher expression of the four target genes in gills and skin of sea bass suggests that this AMPP represents a first and immediate line of defense in combating pathogens and stressors since these tissues constitute the first physiological barriers of the animal.

Mast cell responses to Ergasilus (Copepoda), a gill ectoparasite of sea bream

Immunocytochemical, light microscopy and ultrastructural studies were conducted on gill of sea bream, Sparus aurata L., naturally parasitized with the important parasitic copepod Ergasilus sp. to assess pathology and cellular responses. Thirty-seven S. aurata were examined from a fish farm; 26 (70%) were parasitized, with infection intensity ranging from 3 to 55 parasites per fish. Hosts were divided into two groups, lightly infected fish (<15 parasites per fish) and heavily infected fish (>15 parasites per fish). In histological sections, the copepod encircled gill lamellae with its second antennae, compressed the epithelium, provoked hyperplasia and hemorrhage, occluded arteries and often caused lamellar disruption. Fusion of the secondary lamellae due to epithelial hyperplasia was common in all infected fish; heavily infected fish showed more intense branchial inflammation. In both healthy and infected fish, mast cells (MCs) were free within the connective tissue inside and outside the blood vessels of the primary lamellae and made close contact with vascular endothelial cells, mucous cells and rodlet cells (RCs). MCs were irregular in shape with a cytoplasm filled by numerous electron-dense, membrane-bound granules. Immunostaining of primary and secondary gill filaments with an antibody against the antimicrobial peptide (AMP) piscidin 3 (anti-piscidin 3 antibody, anti-HAGR) revealed a subpopulation of MCs that were positive. These MCs were more abundant in gills of heavily infected fish than in either lightly infected or uninfected fish (ANOVA, P<0.05). Our report documents the response of gill to ectoparasite infection and provides further evidence that mast cells and their AMPs may play a role in responding to branchial ectoparasite infections.

Cod cathelicidin: isolation of the mature peptide, cleavage site characterisation and developmental expression

Cathelicidin antimicrobial peptides are multifunctional peptides that are important in the innate immune system of mammals. Cathelicidins have been identified in several fish species. In this study we have isolated cathelicidin from Atlantic cod (Gadus morhua) and identified the cleavage site from the cathelin propart. This is the first isolation of a cathelicidin from teleost fish. The mature cathelicidin was found to be a 67-residues peptide, highly cationic with a pI of 13. Reversed phase chromatographic fractions containing the purified peptide had pronounced antimicrobial activity and the activity of the mature peptide was confirmed using a synthetic peptide. We examined the expression of cathelicidin during cod larvae early development using real-time PCR and detected expression that varied in the course of the first 68 days post hatching (dph). Two groups of larvae having a different food regime were compared. Cathelicidin expression was found to differ between the two groups and this could be linked to their food input. The presence and rapid adjustment of cathelicidin expression in the larvae indicate that the immune system of cod is active from early on in development and responds to external stimuli by the production of antimicrobial peptides.

Applications of antimicrobial peptides from fish and perspectives for the future

Fish are a major component of the aquatic fauna. Like other organisms, fish secrete different kinds of antimicrobial peptides (AMPs), which are positively charged short amino-acid-chain molecules involved in host defense mechanisms. Environmental hazards and the greenhouse effect have led to increased evolution of drug- and vaccine-resistant pathogenic strains, and it is necessary to find new drugs with structural uniqueness to fight them. Aquatic sources contain thousands of fish species, and each secretes AMPs with structural differences which can be used by the pharmaceutical industry in its search for novel drugs to treat drug-resistant pathogens. Not only limited to antimicrobial functions, AMPs possess other desirable characteristics which may be exploited in the near future. In this review, we list fish AMPs available from published reports, and discuss application-oriented functions of these AMPs. Notably, the possibilities of using fish AMPs as antimicrobial agents, vaccine adjuvants, inactivated vaccines, and antitumor agents are discussed in this review.

Evidence for synergism of the antimicrobial peptide piscidin 2 with antiparasitic and antioomycete drugs

Piscidins are potent, broad-spectrum, host-produced antimicrobial peptides (AMPs) that appear to constitute the most common AMP family in teleost fish. Here, we show that piscidin 2 has potent activity against the water mould Saprolegnia, one of the most important pathogens of freshwater fish. The minimum oomyceticidal concentration (MOC₁₀₀) of piscidin 2 against zoospores of three pathogenic isolates of Saprolegnia ranged from 12.5 to 25.0 μg mL⁻¹. This piscidin concentration is well within levels that have been estimated to be present in at least some fish (1-32.5 μg mL⁻¹). In the presence of either copper or malachite green, two drugs commonly used to treat water moulds, there was evidence for partial synergism (PSYN) with piscidin 2. There was also evidence for PSYN after exposure of the ciliate parasite Tetrahymena pyriformis to piscidin 2 plus copper. Our data provide further evidence that piscidins may be an important host defence against skin and gill pathogens and that the piscidin levels in host tissue might influence the success of drug treatments.

Quantitative enzyme-linked immunosorbent assay determination of an abundant hemoglobin-derived anti-infective peptide in human placenta

A fragment of the human beta-chain of hemoglobin (HEM), hHEMbeta111-146, was shown to have broad antimicrobial properties. The 3.9-kDa peptide was postulated to occur in high concentrations in placenta tissue. We established a reliable method to quantify hHEMbeta111-146 in placenta tissue. Our methodology consists of a tissue extraction step (step 1), a chromatographic enrichment step (step 2), and a final quantification step (step 3) by enzyme-linked immunosorbent assay (ELISA). The specificity of the ELISA reaction was confirmed by parallel analysis of the samples via Western blot (step 4). The ELISA measured the absorbance of a tetramethylbenzidine substrate at 450nm. It showed no cross-reactivity with the corresponding gamma- and alpha-HEM regions and low cross-reactivity with the beta-HEM region and full-length HEM. The sample preparation procedure enabled a prepurification of hHEMbeta111-146, completely eliminating cross-reactive proteins and HEM peptides. The linear range of detection in step 3 was 20-200ng/well (200-2000microg/L) with a limit of quantification of 23ng/well (230microg/L) and a limit of detection of 7ng/well (70microg/L). The assay was characterized by good linearity (r(2)>0.99), intraday precision (coefficient of variation [CV]=2.2-8.3%), interday precision (CV=1.8-9.1%), and accuracy (76-109%). The mean recovery of the ELISA was determined to be 97%, and the overall recovery during steps 1-3 was found to be 40.3+/-2.5%. We measured concentrations from 0.28 to 0.74mg/g placenta tissue of the hHEMbeta111-146 in different placenta samples with an average concentration of 0.57mg/g. This abundant concentration supports an important physiological role of hHEMbeta111-146 in the placenta infective barrier.

Detection of antimicrobial peptides related to piscidin 4 in important aquacultured fish

Epithelial surfaces of fish, such as the gut, skin and gills, comprise a large surface area for possible pathogen invasion. Antimicrobial peptides (AMPs), innate immunity components, play a significant role in protecting fish. Piscidins are a family of AMPs. In this study, we detected the presence of the recently discovered piscidin 4 via bug blot, Western blot, ELISA and/or immunohistochemistry in striped bass (Morone saxatilis), white bass (M. chrysops), European seabass (Dicentrarchus labrax), gilthead seabream (Sparus aurata), red drum (Sciaenops ocellatus), and barramundi (Lates calcarifer). Via bug blot, gill extracts from all species had antibacterial activity corresponding to the migration rate of piscidin 4. Western blotting showed that piscidin 4 immunoreactivity was greatest in striped bass gill extract. The concentrations of piscidin 4 detected by the ELISA in striped bass gill (approximately 20 microg/ml) were well within the levels that are inhibitory to important fish bacterial pathogens. Piscidin 4 was also detected via immunohistochemistry in all fish except barramundi. Piscidin 4-positive cells were identified as mast cells (MC), but not all MC were piscidin 4-positive. Species, age, size and physiological condition at sampling were some factors that might affect piscidin expression in different species. Our data provide strong evidence that piscidin 4 isoforms are present in all these commercially important species.