Effect of size and temperature on the quantity of immunoglobulin in channel catfish, Ictalurus punctatus

Climate change can impair bacterial pathogen defences in sablefish via hypoxia-mediated effects on adaptive immunity

Low-oxygen levels (hypoxia) in aquatic habitats are becoming more common because of global warming and eutrophication. However, the effects on the health/disease status of fishes, the world's largest group of vertebrates, are unclear. Therefore, we assessed how long-term hypoxia affected the immune function of sablefish, an ecologically and economically important North Pacific species, including the response to a formalin-killed Aeromonas salmonicida bacterin. Sablefish were held at normoxia or hypoxia (100% or 40% air saturated seawater, respectively) for 6-16 weeks, while we measured a diverse array of immunological traits. Given that the sablefish is a non-model organism, this involved the development of a species-specific methodological toolbox comprised of qPCR primers for 16 key immune genes, assays for blood antibacterial defences, the assessment of blood immunoglobulin (IgM) levels with ELISA, and flow cytometry and confocal microscopy techniques. We show that innate immune parameters were typically elevated in response to the bacterial antigens, but were not substantially affected by hypoxia. In contrast, hypoxia completely prevented the ∼1.5-fold increase in blood IgM level that was observed under normoxic conditions following bacterin exposure, implying a serious impairment of adaptive immunity. Since the sablefish is naturally hypoxia tolerant, our results demonstrate that climate change-related deoxygenation may be a serious threat to the immune competency of fishes.

Production and characterization of a mouse monoclonal antibody against smallmouth bass (Micropterus dolomieu) IgM

A murine monoclonal antibody (mAb, IgG2a) was produced for the detection of smallmouth bass (Micropterus dolomieu) immunoglobulin (IgM). The antibody is specific for IgM heavy chain and was shown to also recognize the Ig heavy chain of largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus) using Western Blot analysis of plasma from 9 teleost taxa. When applied to the analysis of smallmouth bass total plasma IgM using ELISA, the mAb was found to be effective when used in an inhibition kinetic assay.

Fluctuation of biochemical, immunological, and antioxidant biomarkers in the blood of beluga (Huso huso) under effect of dietary ZnO and chitosan-ZnO NPs

The objective of the present study was to investigate the effects of dietary supplementation with zinc oxide (ZnO) and chitosan-zinc nanoparticles (chitosan-ZnO NPs) on biochemical, immunological, and antioxidant biomarkers in blood of juvenile belugas (Huso huso). The beluga juveniles with initial weight of 287 ± 46 g were fed with eight experimental diets containing 0 g kg^-1 ZnO (the control diet); 10, 20, and 40 mg kg^-1 ZnO; and 10, 20, and 40 mg kg^-1 chitosan-ZnO NPs and 36 mg kg^-1 chitosan. After 28 days of culture, the fish were fed with ZnO and chitosan-ZnO NP-supplemented diets showed a more significant increase in total antioxidant capacity (TAC), superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), glutathione peroxidase (GPX), and glutathione S-transferase (GST) activity (p < 0.05) compared to the control group. There were no significant differences (p > 0.05) in malondialdehyde (MDA) and glucose level in all treatment groups. The results showed that with increasing levels of ZnO and chitosan-ZnO NPs, alternative complement activity (ACH50), and total immunoglobulin, total protein, albumin, and lysozyme had a significant increase in fish fed with ZnO and chitosan-ZnO NP-supplemented diets compared to the control group (p < 0.05). ALP, ALT, and AST enzyme activities showed significant difference between control and treatment groups (p > 0.05), while the levels of LDH enzyme activity, urea, and creatinine decreased by increasing both ZnO and chitosan-ZnO NP levels. These results demonstrated that dietary chitosan-ZnO NPs could improve the health status, immune function, and antioxidant capacity of the cultured beluga juvenile.

The effects of quercetin on immunity, antioxidant indices, and disease resistance in zebrafish (Danio rerio)

The main purpose of this study was to evaluate the immunity, antioxidant indices, and disease resistance of quercetin in zebrafish (Danio rerio). A total of 630 fish were assigned to 21 tanks with 30 fish/tank, and they were exposed to 0, 0.01, 0.1, 1, 10, 100, and 1000 μg/L quercetin, respectively, for 56 days. Results indicated that the immune indices including acid phosphatase (ACP), myeloperoxidase (MPO), lysozyme activities, and Complement 3 (C3), C4, IgM contents were significantly higher in 1 μg/L quercetin group than these parameters in the control group (P < 0.05). TNF-α and IL-8 mRNA expressions significantly decreased as the levels of quercetin increased up to 1 μg/L and increased thereafter (P < 0.05). 1 and 10 μg/L quercetin groups showed significantly lower TNF-α and IL-8 mRNA levels than the quercetin-free group. Transforming growth factor-β and IL-10 mRNA levels showed an obviously opposite trend with TNF-α expression. The SOD, GPX, CAT, T-AOC activities, and SOD and GPX gene expression in the liver were enhanced with increasing quercetin up to 1 μg/L, and decreased thereafter. MDA contents were affected by quercetin, in which 1 and 10 μg/L quercetin had a significantly lower level than that of the control group (P < 0.05). Defensin and Leap-II mRNA expression in the liver were the highest for fish exposed to 1 μg/L quercetin. The fish that exposed to 1 μg/L quercetin also showed a significantly higher survival rate than these of fish exposed to 0, 0.01, and 1000 μg/L quercetin (P < 0.05). In conclusion, the optimal level of quercetin promotes immunostimulant properties, antioxidant indices, and disease resistance of zebrafish.

Screening of immuno-modulatory potential of different herbal plant extracts using striped catfish (Pangasianodon hypophthalmus) leukocyte-based in vitro tests

Many medicinal plants have been shown to possess biological effects, including immuno-modulatory activities on human and other mammals. However, studies about the potential mechanisms of plant extracts on the humoral and tissular immunities in fish have received less attention. This study aimed to screen the immunestimulating properties of 20 ethanol plant extracts on striped catfish Pangasianodon hypophthalmus leukocytes. The peripheral blood mononuclear cells (PBMCs) and head kidney leukocytes (HKLs) of striped catfish (50 ± 5 g per fish) were stimulated at 10 and 100 μg of each plant extract per mL of cell culture medium. Several humoral immune parameters (lysozyme, complement and total immunoglobulin) were examined at 24-h post stimulation (hps). Furthermore, the responses of four cytokine genes, namely il1β, ifrγ 2a and b, and mhc class II were assessed by quantitative real-time PCR at 6, 12, 24, and 48 hps. The results showed that lysozyme, complement as well as total immunoglobulin levels in both PBMCs and HKLs were regulated by some of the plant extracts tested in a concentration-dependent manner; some plant extracts induced the highest immune responses at the low dose (10 μg mL^-1) while others were more efficient at high dose (100 μg mL^-1). Among the extracts, five extracts including garlic Allium sativum L. (As), neem Azadirachta indica A. Juss (Ai), asthma-plant Euphorbia hirta L. (Eh), bhumi amla Phyllanthus amarus Schum. et Thonn (Pa), and ginger Zingiber officinale Rosc (Zo) induced significant changes in the expression of pro-inflammatory cytokine (il1β), antiviral cytokines (ifrγ 2a and b) and adaptive immune cytokine (mhc class II) in striped catfish cells. Pa always modulated the strongest expression of the four cytokines in PBMCs and HKLs over the whole experimental period (p < 0.05), whereas Zo did not stimulate the mhc class II expression in striped catfish leukocytes throughout experimental periods. These in vitro results demonstrated that some plant extracts could differently modulate great potential immune response in fish, supporting their applications in further in vivo experiments.

Estrogen-dependent seasonal adaptations in the immune response of fish

Clinical and experimental evidence shows that estrogens affect immunity in mammals. Less is known about this interaction in the evolutionary older, non-mammalian, vertebrates. Fish form an excellent model to identify evolutionary conserved neuroendocrine-immune interactions: i) they are the earliest vertebrates with fully developed innate and adaptive immunity, ii) immune and endocrine parameters vary with season, and iii) physiology is constantly disrupted by increasing contamination of the aquatic environment. Neuro-immuno-endocrine interactions enable adaption to changing internal and external environment and are based on shared signaling molecules and receptors. The presence of specific estrogen receptors on/in fish leukocytes, implies direct estrogen-mediated immunoregulation. Fish leukocytes most probably are also capable to produce estrogens as they express the cyp19a and cyp19b - genes, encoding aromatase cytochrome P450, the enzyme critical for conversion of C19 steroids to estrogens. Immunoregulatory actions of estrogens, vary among animal species, and also with dose, target cell type, or physiological condition (e.g., infected/non-infected, reproductive status). They moreover are multifaceted. Interestingly, season-dependent changes in immune status correlate with changes in the levels of circulating sex hormones. Whereas E2 circulating in the bloodstream is perhaps the most likely candidate to be the physiological mediator of systemic immune-reproductive trade-offs, leukocyte-derived hormones are hypothesized to be mainly involved in local tuning of the immune response. Contamination of the aquatic environment with estrogenic EDCs may violate the delicate and precise allostatic interactions between the endogenous estrogen system and the immune system. This has negative effects on fish health, but will also affect the physiology of its consumers.

Effects of dietary onion (Allium cepa) powder on growth, innate immune response and hemato-biochemical parameters of beluga (Huso huso Linnaeus, 1754) juvenile

The present study was aimed at determining the effects of dietary onion powder on growth, innate immune response and hemato-biochemical parameters of beluga juvenile (Huso huso). Basal diets containing onion powder 0 (control), 0.5 and 1% of feed were fed to beluga juvenile. At the end of the experiment, the highest weight gain (WG%) and specific growth rate (SGR) was observed in group fed with 1% onion (P < 0.05). There were no significant difference (P > 0.05) about feed conversion ratio (FCR) in treatment groups that fed diets containing various levels of onion powder. After 8 weeks, serum lysozyme activity, superoxide dismutase activity (SOD), respiratory burst activity and serum total immunoglobulin (Ig) showed a significant increase in treatment group with 1% onion powder compared to other groups (P < 0.05). The group fed 1% onion showed a significantly increases in the number of erythrocytes (RBC), leucocyte (WBC), haematocrit (Hct) levels compared to the control group (P < 0.05). Haemoglobin, monocyte, lymphocyte and neutrophil had no significant change (P > 0.05) in treatment groups and control. The analysis of AST and LDH levels showed a significant decrease in 1% onion compared to the control and 0.5% onion diet (P < 0.05), while ALT and ALP levels were not influenced (P > 0.05). The blood glucose, total protein, triglyceride, cholesterol, albumin and globulin levels were lower in treated groups compared with the control (P < 0.05). The results of this study demonstrated that dietary onion powder could be an improvement in growth, hematological parameters and immune function of beluga juvenile.

Effects of fenugreek (Trigonella foenum graecum) on gilthead seabream (Sparus aurata L.) immune status and growth performance

The possible effect of dietary administration of fenugreek (Trigonella foenum graecum) on gilthead seabream (Sparus aurata L.) immune status and growth performance was studied. Fish were divided into 4 groups before being fed with commercial diet supplemented with 0% (control), 1%, 5% and 10% of fenugreek seeds for 4 weeks. The effects of the diets were analysed on the cellular (respiratory burst activity and leucocyte peroxidase content) and humoral (complement activity, antiprotease, total protein, peroxidase, and IgM level) immune parameters, as well as growth and haematological parameters (WBC and RBC counts). The results recorded enhancement in all the assayed parameters in fish fed fenugreek diets comparing to control fish. The expression of several immune-related genes in head-kidney (MHC1, CSF-1R, IL-8, and IgM) and different antioxidant enzyme genes in liver (GR, CAT and SOD) of seabream specimens were also investigated. Again, the highest fenugreek doses tested provoked significant up-regulation in most of immune-related genes and antioxidant enzyme genes (p < 0.05). No adverse effects were observed on intestine and liver morphology on fish fed fenugreek diets. The present results suggest that the fenugreek seed, specially the highest dosage used in the present work could be considered a good food supplement to improve the immune status and increase the production of gilthead seabream.

Physiology and immunology of mucosal barriers in catfish (Ictalurus spp.)

The mucosal barriers of catfish (Ictalurus spp) constitute the first line of defense against pathogen invasion while simultaneously carrying out a diverse array of other critical physiological processes, including nutrient adsorption, osmoregulation, waste excretion, and environmental sensing. Catfish depend more heavily on mucosal barriers than their terrestrial counterparts as they are continuously interacting with the aquatic microbiota. Our understanding of these barriers, while growing, is still limited relative to that of mammalian model systems. Nevertheless, a combination of molecular and cellular studies in catfish over the last few decades, and particularly within the last few years, has helped to elucidate many of the primary actors and pathways critical to their mucosal health. Here we describe aspects of innate and adaptive immune responses in the primary mucosal tissues (skin, gill, and intestine) of catfish, focusing on mucus-driven responses, pathogen recognition, soluble mediators, and immunoglobulin and T-cell derived immunity. Modulation of mucosal barriers will be critical moving forward for crafting better diets, improving vaccine delivery, enhancing water quality, and ensuring sustainable production practices in catfish.

Effects of dihydroquercetin obtained from deodar (Cedrus deodara) on immune status of gilthead seabream (Sparus aurata L.)

The use of medicinal plants as prophylactic method in fish is considered safe and a very promising alternative to the use of chemicals in aquaculture practices. The prospective mode of action of dihydroquercetin, fraction of the medical plant deodar (Cedrus deodara), was evaluated on immune status of gilthead seabream (Sparus aurata L.). Fish were divided into 4 groups before being fed for 14 days with commercial diets supplemented with 0% (control), 0.1%, 0.5% and 1% of dihydroquercetin. Cellular (phagocytosis and respiratory burst activities) and humoral (seric complement activity, antiprotease, total protein, peroxidase, bactericidal activity and IgM level) immune parameters were investigated. The results recorded enhancement in all the tested parameters and in all the dihydroquercetin supplemented groups compared to the control. Interestingly, the fish received the lowest dose of dihydroquercetin (0.1%) showed a highly significant difference (p < 0.05) in phagocytosis, respiratory burst, IgM level, total protein, complement, antiprotease and bactericidal activities compared to the control. Direct effect of different doses of dihydroquercetin on head-kidney leucocytes was also studied in a previous in vitro assay. Again, the lowest doses tested provoked the highest immune cellular activities, where, the highest phagocytic and respiratory bust activities were recorded in leucocytes incubated with 0.025% and 0.0125% doses, respectively. Therefore, the results suggest that low concentrations of dihydroquercetin as food supplements are able to increase the immune status of gilthead seabream.

Detection and characterization of phospholipase A(2) (PLA(2)) in Caiman latirostris and Caiman yacare plasma

Reptiles have proven to have a versatile and efficient nonspecific immune system adapted to the environments in which they commonly live. Phospholipase A(2) (PLA(2)) is important hydrolytic enzyme involved in the regulation of specific types of messengers, with significant roles in the innate immune response. A number of agents that exert effects on cellular receptors emit a series of signals leading to the increased activity of PLA(2). Phospholipase A(2) has been identified and characterized in temperature, plasma concentration, and kinetic dependence in two species of caiman. The results of these studies suggest that the high PLA(2) activities observed in caiman plasma may be an important component of a well-developed innate immunity. Based on the knowledge of their properties, this powerful immunologic component should be evaluated as a possible application in the veterinary or even human therapeutic industry. Additionally, this is another reason to consider these animals excellent models for the study of immune phylogenetic mechanisms.

Haematological and innate immune responses in Puntius sarana: normal range and seasonal variation

A study was conducted to measure the normal ranges, seasonal and annual variations in haematological and immune parameters of juvenile healthy Puntius sarana (weighing 75–100 g) during three major seasons over two consecutive years. Significantly (P<0.05) lower serum myeloperoxidase and ceruloplasmin activities, superoxide production, plasma glucose level, packed cell volume and haemoglobin concentration were detected in winter as compared to the summer season. However, serum lysozyme activity, antiprotease activity, total erythrocyte count (TEC) and TLC profiles were consistent during all seasons. The reference intervals (25th–75th) of each parameter were estimated and a range was established. The annual changes in immune parameters with minimum and maximum values were measured and a significant variation was noticed in myeloperoxidase, antiprotease, total protein levels and TEC over two consecutive years. The lower levels in haematological and innate immune status of fish during winter possibly indicate a higher disease risk period for the species.

Temperature effects on immune response and hematological parameters of channel catfish Ictalurus punctatus vaccinated with live theronts of Ichthyophthirius multifiliis

This study evaluated the influence of temperature on the immune responses and hematological parameters in channel catfish Ictalurus punctatus immunized via intraperitoneal injection with live theronts of Ichthyophthirius multifiliis. Fish were distributed in 18 aquaria and received 9 treatments: 4 groups of fish were vaccinated with live theronts and maintained at constant temperature 15 °C, 20 °C, 25 °C and 30 °C; 3 groups of fish vaccinated and subjected to cycling temperature regime from 15-25 °C, 20-25 °C and 20-30 °C, changed 5 °C each day; 2 groups of fish were not vaccinated and served as controls at 25 °C, one with Ich challenge and the other without challenge. Non vaccinated fish and those vaccinated at 15 °C or 15-25 °C did not show anti-Ich antibodies in the serum 14 and 21 days post-immunization. The antibody levels were significantly higher from fish vaccinated at 25 °C, 30 °C, 20-25 °C and 20-30 °C compared to fish at 15 °C, 20 °C and 15-25 °C both 14 and 21 days post-immunization. At constant water temperature, fish vaccinated at 15 °C showed significantly higher mortality rate (67.8%, P < 0.05) than those vaccinated at 20 °C, 25 °C, and 30 °C (0-10.7% mortalities). At cycling water temperature, fish vaccinated at 15-25 °C showed significantly higher mortality rate (67.8%) than those vaccinated at 20-25 °C and 20-30 °C (P < 0.05). Twenty days after immunization fish vaccinated at 30 °C and 20-30 °C showed significant increase in the red blood cells, white blood cells, thrombocytes and monocytes. Six days after challenge with I. multifiliis theronts the fish showed decreased white blood cells, thrombocytes and monocytes. This study suggests that vaccinated catfish were severely impacted by low temperature, either at 15 °C constant temperature or at 15-25 °C cycling temperature. The fish showed no anti-Ich antibodies and suffered high mortality similar to non vaccinated control fish.

Development and characterization of rifampicin-resistant mutants from high virulent strains of Flavobacterium columnare

Flavobacterium columnare is divided into three genetic groups or genomovars, genomovar II being highly virulent for channel catfish. A modified live vaccine is currently available to prevent columnaris disease under the licensed name Aquavac-Col(®) . The strain of F. columnare used to generate the avirulent rifampicin-resistant mutant used in Aquavac-Col(®) belonged to genomovar I, the less virulent group towards channel catfish. In this study, we describe the generation and characterization of rifampicin-resistant mutants from genomovar II strains. A total of 13 new mutants were obtained, and eight of them (two from each parent strain) were genetically and phenotypically characterized. Highly conserved regions within the ribosomal operons were identical between parent and mutant strains. Genetic differences between mutants and their parent strains were revealed by amplified fragment length polymorphism (AFLP). Genetic changes were distinctive among different mutants. Analysis of the lipopolysaccharide (LPS) showed that while some mutants lacked a few molecular bands of the LPS, some exhibited the same LPS profiles as their parent strains. Comparison between immunogenic proteins from mutants and parents was carried out by immunoblot analysis and further confirmed the uniqueness of individual mutants. A complete set of rifampicin-resistant mutants with different genetic and immunogenic properties from the highly virulent genomovar II has been created. These mutants may have the potential of becoming vaccine candidates against columnaris disease.

Isolation and characterization of immunoglobulin M of Asian sea bass, Lates calcarifer and its level in serum

Asian sea bass immunoglobulin M (IgM) was purified from the sera of Lates calcarifer by affinity chromatography. Analysis of the purified IgM on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing and non-reducing conditions revealed that the sea bass IgM was a tetrameric protein with a molecular weight of 896 kDa; it contained an equimolar heavy chain and light chain with molecular weight of 83 kDa and 27 kDa respectively. However, besides the covalently linked tetrameric IgM, noncovalently linked tetramer dissociated into dimeric and monomeric forms also demonstrated by non-reducing SDS-PAGE. Carbohydrate moieties were found to be linked with both heavy and light chains. A polyclonal rabbit anti-Asian sea bass IgM was prepared which showed a specific reaction of anti-fish IgM antibody with IgM of sea bass. Sea bass IgM concentration was determined in the serum by indirect ELISA. The average IgM concentration in the sera of the healthy sea bass was 5.4±1.8 mg ml−1; it amounted to 16.7% of the total serum protein.

Immunological control of fish diseases

All metazoans possess innate immune defence system whereas parameters of the adaptive immune system make their first appearance in the gnathostomata, the jawed vertebrates. Fish are therefore the first animal phyla to possess both an innate and adaptive immune system making them very interesting as regards developmental studies of the immune system. The massive increase in aquaculture in recent decades has also put greater emphasis on studies of the fish immune system and defence against diseases commonly associated with intensive fish rearing. Some of the main components of the innate and adaptive immune system of fish are described. The innate parameters are at the forefront of immune defence in fish and are a crucial factor in disease resistance. The adaptive response of fish is commonly delayed but is essential for lasting immunity and a key factor in successful vaccination. Some of the inherent and external factors that can manipulate the immune system of fish are discussed, the main fish diseases are listed and the pathogenicity and host defence discussed. The main prophylactic measures are covered, including vaccination, probiotics and immunostimulation. A key element in the immunological control of fish diseases is the great variation in disease susceptibility and immune defence of different fish species, a reflection of the extended time the present day teleosts have been separated in evolution. Future research will probably make use of molecular and proteomic tools both to study important elements in immune defence and prophylactic measures and to assist with breeding programmes for disease resistance.

Cloning, expression, and immunogenicity of Flavobacterium columnare heat shock protein dnaJ

The Flavobacterium columnare heat shock protein (HSP) gene dnaJ* was isolated, cloned, expressed, and used as an antigen in a recombinant vaccine strategy for channel catfish Ictalurus punctatus. The F. columnare dnaJ* sequence was obtained from genomovars I and II and showed intraspecies variability. Recombinant protein was expressed and purified from Escherichia coli cultures and injected intraperitoneally (12 microg of purified DnaJ/fish) into fingerling channel catfish. In addition, induced (expressing the recombinant DnaJ) and uninduced (no recombinant protein being produced) E. coli cultures were also used to immunize fish. At 28 d postimmunization, antibody response was evaluated and the fish were challenged with F. columnare. A specific immune response against DnaJ was observed in fish immunized with DnaJ or E. coli cultures expressing DnaJ. No protection against the disease, however, was observed in F. columnare-challenged fish that had been immunized with DnaJ. Some level of protection was observed in fish immunized with uninduced and induced E. coli lysates. Although HSPs have been shown to be immunodominant and good candidates for subunit vaccines in other animals, DnaJ failed to protect against columnaris disease in channel catfish.

Warmwater fish vaccinology in catfish production

The ability of the fish industry to provide a continuous supply of fish protein depends on both proper biosecurity and strategies to significantly reduce the risk of infectious diseases. Vaccination is a safe and effective means to prevent disease and to increase the productivity and profitability of farmed fish. Vaccines are likely to be the prime prophylactic measure of the future because of rapidly developing advances in fish vaccine technology and producer acceptance. The efficacy of a vaccine is influenced by a variety of factors that must be considered in the development of vaccination strategies for fish. This review highlights some of these factors. The response to a modified live vaccine against Edwardsiella ictaluri is used for illustration.

Comparison of lipopolysaccharide and protein profiles between Flavobacterium columnare strains from different genomovars

Lipopolysaccharide (LPS) and total protein profiles from four Flavobacterium columnare isolates were compar. These strains belonged to genetically different groups and/or presented distinct virulence properties. Flavobacterium columnare isolates ALG-00-530 and ARS-1 are highly virulent strains that belong to different genomovars while F. columnare FC-RR is an attenuated mutant used as a live vaccine against F. columnare. Strain ALG-03-063 is included in the same genomovar group as FC-RR and presents a similar genomic fingerprint. Electrophoresis of LPS showed qualitative differences among the four strains. Further analysis of LPS by immunoblotting revealed that the avirulent mutant lacks the higher molecular bands in the LPS. Total protein analysis displayed by immunoblotting showed differences between the strains analysed although common bands were present in all the isolates. FC-RR lacked two distinct common bands (34 and 33 kDa) shared by the other three isolates. Based on the difference of LPS and total protein profiles, it is possible to discriminate the attenuated mutant FC-RR from other F. columnare strains.

Antibody repertoire development in teleosts--a review with emphasis on salmonids and Gadus morhua L

The group of teleosts is highly diverse, comprising more than 23000 extant species. Studies of the teleost antibody repertoire have been conducted in many different species within different orders, though some species and families have been better characterised than others. The Atlantic cod (Gadus morhua L.) and several species within the Salmoninae (e.g. Salmo salar and Oncorynchus mykiss) are among the best-studied teleosts in terms of the antibody repertoire. The estimated size of the repertoire, the organisation of immunoglobulin (IG) gene segments, the expressed IG repertoire, the IgM serum concentration, and the serum antibody responses reveal some fundamental differences between these species. The serum IgM concentration of G. morhua is some ten times higher than that of S. salar, though G. morhua is characterised as a 'low' (or 'non') responder in terms of specific antibody production. In contrast, an antibody response is readily induced in S. salar, although the response is strongly regulated by antigen induced suppression. The IGHD gene of G. morhua has a unique structure, while the IGHM and IGHD genes of S. salar have a characteristic genomic organisation in two parallel loci. In addition, salmonids, express a broad repertoire of IGH and IGI V-region gene segments, while a single V gene family dominates the expressed heavy and light chain repertoire of G. morhua. Little is known about the developing antibody repertoire during ontogeny, in different stages of B-cell maturation, or in separate B-cell subsets. Information on the establishment of the preimmune repertoire, and the possible role of environmental antigens is also sparse.

Channel catfish immunoglobulins: repertoire and expression

The channel catfish, Ictalurus punctatus, is widely recognized as an important model for studying immune responses in ectothermic vertebrates. It is one of the few fish species for which defined viable in vitro culture systems have been established and is currently the only fish species from which a variety of functionally distinct clonal leukocyte lines are available. Moreover, there is a large basis of biochemical and molecular information on the structure and function of catfish immunoglobulins (Igs). Catfish, as other teleosts, have a tetrameric homolog of IgM as their predominant serum Ig plus a homolog of IgD. They also have genetic elements basically similar to those of mammals, which encode and regulate their expression. The catfish Ig heavy (H) chain locus is a translocon-type locus with three Igdelta genes linked to an Igmu gene or pseudogene. The catfish IgH locus is estimated to contain approximately 200 variable (V) region genes representing 13 families as well as at least three diversity (D) and 11 joining (JH) genes. The catfish has two light (L) chain isotypes, F and G, both encoded by loci organized in multiple cassettes of VL-JL-CL with the VL in the opposite transcriptional orientation. Hence, all requisite components for encoding antibodies are present in the catfish, albeit with certain variations. In the future, whether or not additional unique features of Ig function and expression will be found remains to be determined.

Cutaneous antibodies from channel catfish, Ictalurus punctatus (Rafinesque), immune to Ichthyophthirius multifiliis (Ich) may induce apoptosis of Ich theronts

This study explored the existence of apoptosis (programmed cell death) in Ichthyophthirius multifiliis Fouquet (Ich) theronts and determined the effect of cutaneous antibodies in skin culture fluid from fish immune to Ich on theront apoptosis. Apoptosis was detected in theronts and was clearly distinguished by fluorescent microscopy after staining with acridine orange and propidium iodide. The apoptotic theronts showed characteristic chromatin condensation and nuclear fragments containing chromatin pieces. The externalization of phosphatidylserine on the plasma membrane of apoptotic theronts was detected with fluorescein isothiocyanate-conjugated annexin using flow cytometry. Theront apoptosis was induced using the skin culture fluid from fish immune to Ich, which contained cutaneous antibodies against Ich. The highest apoptosis appeared in theronts exposed to immune skin culture fluid at a 1:10 dilution, compared with those at 1:20 and 1:40 dilutions. A direct correlation was noted between the percentage of apoptotic theronts and exposure duration to immune skin culture fluid. The study indicated that antibody reaction with theronts (immobilization) played an important role in theront apoptosis, but it could not be excluded that other components released from the excised skin had effects on theronts.

Total serum immunoglobulin M levels are affected by immunomodulators in seabream (Sparus aurata L.)

Immunoglobulin M (IgM) is a major component of the teleost humoral immune system. Despite the significance of IgM levels as an immune parameter, there are relatively few studies on changes induced in its total levels in serum. This study examines the effects of several immunomodulators (vitamin A, chitin, yeast cells or levamisole, which act as immunostimulants, and crowding, hypoxia or anaesthetics, which act as stressors) upon the total serum IgM levels of non-immunized gilthead seabream (Sparus aurata L.). Total serum IgM levels of fish fed with the assayed immunostimulant-supplemented diets were statistically higher than those in fish fed a non-supplemented diet, especially in the case of levamisole. On the other hand, serum IgM levels of fish subjected to different stressors were not affected by crowding, hypoxia or certain anaesthetics. However, benzocaine and a narcotic dose of 2-phenoxyethanol provoked a great reduction, while quinaldine sulphate increased IgM levels to a significant degree. These results show how the seric IgM levels can be differently affected by some immunomodulators and the important role they may play in the regulation of total circulating IgM levels in seabream. The possibility of using total serum IgM for assessing immunostimulation, disease diagnosis and stress symptoms during fish farming is discussed.

Immune responses and host protection of channel catfish, Ictalurus punctatus (Rafinesque), against Ichthyophthirius multifiliis after immunization with live theronts and sonicated trophonts

The humoral immune responses and host protection of channel catfish, Ictalurus punctatus (Rafinesque), against Ichthyophthirius multifiliis (Ich) were determined after immunization with live theronts and sonicated trophonts. Immunizations with live theronts or sonicated trophonts were carried out by both bath immersion and intraperitoneal (i.p.) injection. Cutaneous and serum immunoglobulin (Ig) levels and anti-Ich antibodies were measured 12 and 21 days post-immunization. The level of Ich infection and survival of catfish were determined after theront challenge. Cutaneous and serum anti-Ich antibodies were significantly higher (P < 0.05) in fish immunized with live theronts by immersion or i.p. injection, or with sonicated trophonts administered by i.p. injection, than in fish immunized with sonicated trophonts by immersion, with bovine serum albumin by i.p. injection, or non-immunized controls. Host protection was noted only in fish immunized with live theronts by immersion or i.p. injection or with sonicated trophonts by i.p. injection. There was a positive correlation between higher levels of anti-Ich antibodies and host survival in the immunized fish.

Feed deprivation of channel catfish, Ictalurus punctatus (Rafinesque), influences organosomatic indices, chemical composition and susceptibility to Flavobacterium columnare

Withholding feed has been suggested as a strategy to manage infectious disease of channel catfish, Ictalurus punctatus (Rafinesque). In a previous study, we demonstrated that deprivation of feed for as little as 7 days reduced innate resistance of catfish to Flavobacterium columnare. This study was conducted to evaluate the effect of feeding regimens [no feeding (NF), fed once every other day to satiation (FEOD) and fed once daily to satiation (FD)] on organosomatic indices, physiological changes and susceptibility of channel catfish to F. columnare. Fish that were not fed for 2 and 4 weeks had a significant increase (P < 0.05) in gutted weight:-wet weight ratio and decrease in other organosomatic indices [gut index (GI), mesenteric fat index (MFI) and hepatosomatic index (HSI)]. Haematology was not effected by feeding regimen except at week 4, when a significantly higher haemoglobin level was observed in the NF fish. Serum protein did not differ at week 2, but the level at week 4 of the NF fish (35.91 mg mL(-1)) was significantly lower than that of the FD fish (41.77 mg mL(-1)). Significantly lower (P < 0.05) blood glucose (39.5 and 40.3 mg dL(-1)) and liver glycogen (1.7 and 1.8 mg g(-1)) were seen in the NF fish at weeks 2 and 4, respectively, as compared with blood glucose and liver glycogen levels of FD fish (67.5 and 92.8 mg dL(-1) and 46.5 and 52.6 mg g(-1) at weeks 2 and 4, respectively) and FEOD (82.8 and 85.5 mg dL(-1) and 45.1 and 51.4 mg g(-1) at weeks 2 and 4, respectively). Mortality in the NF fish caused by F. columnare (78%) was significantly higher (P < 0.05) than mortality in the FD and FEOD treatments (0.0 and 1.7%, respectively). Blood glucose and liver glycogen showed the same trend of low values for NF fish following challenge (week 6). Blood glucose, liver glycogen, GI and HSI are sensitive indicators for channel catfish deprived of feed (NF) for 4 weeks. Blood glucose and liver glycogen levels around 40 mg dL(-1) and 2 mg g(-1), respectively, are indicative of starvation in juvenile channel catfish. Moreover, NF fish were susceptible to F. columnare infection. Thus, it is suggested that in the absence of natural food, juvenile channel catfish should be fed at least once every other day to apparent satiation to maintain normal physiological function and improve resistance to F. columnare.

A comparative study of Edwardsiella ictaluri parent (EILO) and E. ictaluri rifampicin-mutant (RE-33) isolates using lipopolysaccharides, outer membrane proteins, fatty acids, Biolog, API 20E and genomic analyses

The biological properties of Edwardsiella ictaluri RE-33 rifampicin-mutant and its parent strain EILO were analysed. RE-33 is an avirulent isolate used as a modified live vaccine against enteric septicaemia of catfish. Electrophoretic analysis of lipopolysaccharide (LPS) patterns showed high homology between both isolates. Further characterization of LPS by immunoblotting revealed the main differences in LPS composition. The RE-33 isolate lacks the high molecular weight bands of LPS (HMW-LPS). Outer membrane protein analysis also showed some immunological differences between RE-33 and the EILO parent strain. Only two fingerprinting techniques, fatty acid composition analysis and Biolog phenotypic profiles, were able to discriminate between both isolates.

Development of an immunoassay to measure the humoral immune response of hybrid striped bass Morone chrysops x M. saxatilis

Hybrid striped bass (HSB) were immunized with bovine serum albumin (BSA) and the specific anti-BSA immunoglobulin (Ig) was affinity purified from the resulting serum by means of an agarose gel-BSA column. The native Ig had an apparent molecular size of 893 KDD, by size exclusion chromatography, and when examined by polyacrylamide gel electrophoresis (PAGE) under denaturing conditions, resolved to heavy (H) and light (L) chains of 76 and 27 KDD, respectively. Affinity purified native HSB Ig was used to immunize a goat which produced specific anti-HSB Ig antibody (Ab). Purified native HSB Ig was also used to produce two murine monoclonal antibodies (mAbs) with specific affinities for H and L chain moieties of the HSB Ig molecule. Both polyclonal and monoclonal antibodies could be used individually in an indirect enzyme-linked immunosorbent assay (ELISA) to measure specific anti-BSA Ig in HSB serum. These antibodies could also be used in combination to measure total Ig in a capture ELISA format. Using both assays, the kinetics of the humoral immune response of HSB was measured for 98 days following two injections of BSA.

Isolation, Purification, and Molecular Weight Determination of Serum Immunoglobulin from Gulf Menhaden: Development of an Enzyme-Linked Immunosorbent Assay to Assess Serum Immunoglobulin Concentrations from Atlantic Menhaden

An immunoglobulin M (IgM)-like immunoglobulin was isolated by polyethylene glycol precipitation from pooled serum collected from healthy gulf menhaden Brevoortia patronus. The immunoglobulin (Ig) was purified by Sephacryl-400 gel filtration chromatography. The molecular weight of unreduced, purified Ig was determined to be 850 kilodaltons (kD) by high-performance liquid chromatography. A goat antiserum against the purified Ig was produced and determined to react with the serum Ig of both gulf and Atlantic menhaden B. tyrannus by double gel diffusion. When reacted with sera from taxonomically unrelated species of fish, sheepshead minnow Cyprinodon variegatus, striped mullet Mugil cephalus, gulf flounder Paralichthys albigutta, and hybrid striped bass (white bass Morone chrysops × striped bass M. saxatilis), no precipitation bands developed. Furthermore, the specificity of the goat antiserum was shown by Western blot analysis to be for the 77,000-molecular-weight heavy chain of reduced and alkylated gulf and Atlantic menhaden Ig. An indirect enzyme-linked immunosorbent assay (ELISA) was developed for the assessment of Ig concentrations in Atlantic menhaden serum. To illustrate the applicability of the ELISA, we assessed the Ig concentration in the serum of 542 healthy Atlantic menhaden collected from inland bays of Delaware and Maryland in 2000 and 2001. The amount of Ig was estimated to be in the range 0.26-23.50 mg/mL, with a mean of 7.37 and a standard deviation of 5.12 mg/mL. The ELISA was reproducible, as determined by the inter- and intra-assay coefficients of variation (100·SD/mean) of 11.2% and 6.8%, respectively, and used very small amounts (1-2 μL) of serum to assess the Ig concentrations from menhaden.

Humoral immune parameters in Atlantic cod (Gadus morhua L.) I. The effects of environmental temperature

The effects of environmental temperature on certain humoral immune parameters in Atlantic cod (Gadus morhua L.) were studied. Serum samples were collected from captive cod, of wild origin, kept at different temperatures for 12 months. It was found that immunoglobulin and natural antibody levels increased with increasing temperature whereas the total serum protein concentration, anti-protease activity, iron concentration, unsaturated and total iron binding capacity decreased with increasing temperature. Haemolytic activity and percentage iron saturation also tended to decrease with increasing temperature although this was not statistically significant.

Humoral immune parameters in Atlantic cod (Gadus morhua L.) II. The effects of size and gender under different environmental conditions

The effects of size and gender on several humoral immune parameters in cod were examined under different environmental conditions. Serum samples were collected from wild cod of different sizes. Two samplings were undertaken: In the spring in relatively cold waters off the north west coast of Iceland and in the fall in relatively warm waters off the west coast of Iceland. Most of the parameters increased with increasing cod size, except the haemolytic activity which decreased. Higher serum protein levels were seen in cod sampled in the fall than in the spring. In cod sampled in the spring there was an apparent difference between specimens < 75 cm in length and the larger specimens with respect to haemolytic activity and iron concentration. None of the parameters were influenced by the gender of the cod.

Quantification of immunoglobulin in the serum and mucus of channel catfish at different ages and following infection with Edwardsiella ictaluri

An enzyme-linked immunosorbent assay was developed to quantify immunoglobulin (Ig) in the serum and mucus of channel catfish (Ictalurus punctatus). The capture antibody (Ab) was a monoclonal Ab to channel catfish Ig and the detector was a polyclonal goat serum against channel catfish Ig. Detectable levels of channel catfish Ig were 0.1 microgram ml-1 and coefficients of intra- and interassay variations were 20% and 15%, respectively. Serum Ig concentration was found to increase from 0.36 +/- 0.25 to 0.49 +/- 0.26 mg ml-1 between 3 and 15 months of age. In contrast, mucus Ig concentration slightly decreased from 0.55 +/- 0.52 to 0.45 +/- 0.82 ng cm-2 of skin between 3 and 15 months of age. Mucus Ig concentrations were highest immediately caudal to gill covers and between pectoral to anal fins, at concentrations of 0.45 +/- 0.82 and 0.34 +/- 0.67 ng cm-2, respectively. The concentration of mucus Ig between anal and caudal fins and on the ventral skin between gill covers and pectoral fin was 0.18 +/- 0.42 and 0.09 +/- 0.14 ng cm-2, respectively. The kinetics of Ig production following infection with Edwardsiella ictaluri showed that serum Ig concentrations markedly increased (20.92 +/- 32.75 mg ml-1) at 13 days post-infection. The increase in mucus Ig concentrations occurred 14 days later (0.80 +/- 1.91 ng cm-2). Individual variation in both serum and mucus Ig production increased considerably during the course of infection (+/-0.23 to +/-32.75 mg ml-1 for serum Ig and +/-0.1 to +3.41 ng cm-2 for mucus Ig). The results suggest that E. ictaluri infection causes higher Ig production than that found in non-infected fish of the same age. Ab response to E. ictaluri was detected in the serum but not in the mucus of infected fish. Our results show differences in serum and mucus Ig concentrations with age and after infection with E. ictaluri.

The effect of temperature and water quality on antibody response to Aeromonas salmonicida in sunshine bass (Morone chrysops x Morone saxatilis)

The kinetics of the antibody response to Aeromonas salmonicida were determined in sunshine bass (hybrid striped bass: female Morone chrysops X male Morone saxatilis) acclimated to 10, 18, 24, 29 degrees C, and to 0.15 mg 1(-1) un-ionized ammonia and 200 mg 1(-1) nitrate levels. Temperature and water quality factors affected the immune response of sunshine bass. Temperatures of 10 degrees C and 18 degrees C decreased the magnitude and delayed the time of the antibody response to A. salmonicida. The antibody response was not affected at 29 degrees C, which is above the optimal temperature for sunshine bass. Elevated un-ionized ammonia concentrations of 0.15 mg 1(-1) also did not affect the antibody response. Elevated nitrate levels of 200 mg 1(-1), however, decreased the antibody response to the same extent as 18 degrees C water.

Applications of monoclonal antibodies in aquaculture

Monoclonal antibodies (MAbs) currently are being applied to the study of fish immunology and fish infectious diseases. MAbs to fish immunoglobulins (Igs) have helped isolate fish Igs, identify heavy and light chain variants in fish Ig, study the ontogeny of B lymphocytes, and improve techniques for the measurement of fish Ig and specific antibodies (Abs). MAbs have been obtained against several leucocyte surface antigens and are being used as markers for different subsets of fish leukocytes: neutrophils, non-specific cytotoxic cells and cells responsible for the mixed leucocyte reaction. The sensitivity and specificity of many immunoassays for identifying fish pathogens have been improved by the use of MAbs. Further improvement of these tests is currently being attempted by the use of MAbs together with the polymerase chain reaction (PCR). Epizootiological studies of fish diseases are beginning to emerge from the use of these reagents and techniques. In the near future these new methods should detect low levels of pathogens in adult carriers and perhaps in eggs, thus helping to prevent the dissemination of fish diseases. MAbs to fish pathogens are also being used for passive immunization studies as well as for conformational probes in the development of genetically engineered vaccines.

Genetic variation in the humoral immune response against Vibrio salmonicida and in antibody titre against Vibrio anguillarum and total IgM in Atlantic salmon (Salmo salar)

Total IgM level and antibody titre to Vibrio anguillarum O-antigen after bath-vaccination, and specific antibody response to V. salmonicida O-antigen at three different samplings were analysed in family material of Atlantic salmon (Salmo salar), consisting of 791 fish belonging to 34 maternal full-sib groups within 12 paternal half-sib groups. The fish were immunized twice, and blood samples collected three times. After the third blood sampling, the fish were challenged with V. anguillarum. Medium to low genetic variation was recorded in total IgM and in the antibody titres against V. anguillarum O-antigen and V. salmonicida O-antigen, with heritability estimates of 0.12, 0.18 and from 0.03 to 0.12, respectively. Moderate to high genetic and phenotypic correlations were found between the V. salmonicida O-antigen titres at different samplings. Genetic and phenotypic correlations between the initial titres were moderate to low. The effect of different immune traits, including Aeromonas salmonicida A-layer titres (previously described), on the ability to survive the challenge was examined. The likelihood of surviving the challenge was affected positively by the A. salmonicida A-layer titre at the second sampling, and almost significantly affected by the initial V. anguillarum O-antigen titre. Production traits, such as mean slaughter weight and mean proportion of survivors in a corresponding full-sib material, were obtained in the sea-rearing period. No significant full-sib correlation between immune parameters and production traits was detected.

Monoclonal antibodies to turbot (Scophthalmus maximus) immunoglobulins: characterization and applicability in immunoassays

Five monoclonal antibodies (mAbs) to immunoglobulins (Igs) of the turbot Scophthalmus maximus were produced and characterized. All the mAbs (denominated UR1, UR3, UR4, UR6 and UR7) are of isotype IgG1/kappa and show good anti-turbot Ig reactivity in enzyme-linked immunosorbent assay (ELISA) and immunoblotting. Results of competitive ELISA and immunoblotting analysis indicate that these five mAbs react with at least three different epitopes on the turbot Ig H chain. Except in the case of UR1, reactivity with periodate-treated purified turbot Ig was much lower than with the untreated Ig, suggesting that carbohydrate residues are involved in epitope recognition. All the mAbs showed reactivity with sera from the closely related species Scophthalmus rhombus but not with sera from species of other flatfish genera. One of these mAbs (UR3) has been successfully applied for the detection of antibodies against Vibrio anguillarum in ELISA.

Rapid enzyme-linked immunosorbent tests for detecting antibodies to Edwardsiella ictaluri in channel catfish, Ictalurus punctatus, using exoantigen

A rapid enzyme-linked immunosorbent assay (ELISA) was developed to evaluate sera from channel catfish with and without Edwardsiella ictaluri infection. Anti-E. ictaluri antibodies were detected in the sera from 94 of 100 infected catfish. Specific antibodies were not detected in the sera from 100 non-infected fish. The ELISA was based on the Falcon Assay Screening Test (FAST) and was performed in 30 min. An E. ictaluri exoantigen was used in the FAST-ELISA. The immunodominance of the exoantigen was shown by reactivity with monoclonal antibody (MAb) against the predominant epitope of E. ictaluri. The FAST-ELISA was found to be ideal for serodiagnosis and seroepidemiological purposes of detecting and monitoring E. ictaluri antibody responses.

Quantification of low levels of rainbow trout immunoglobulin by enzyme immunoassay using two monoclonal antibodies

An enzyme immunoassay has been developed for quantitation of low levels of trout immunoglobulin (Ig). This assay uses two monoclonal antibodies, one as capture antibody and the other as detector, directed against two non-overlapping epitopes on the heavy chains of trout Ig. The assay shows high reproducibility and can detect 0.12 micrograms trout Ig ml-1. Coefficients of intra- and interassay variation ranged from 3.8 to 7.1% and from 7.9 to 17.4%, respectively. Analysis of 37 healthy trout showed increasing serum Ig concentration with size. The mean Ig concentration was 0.67 mg ml-1 for trout of about 20 g and 9.1 mg ml-1 for trout weighing more than 125 g.