Isolation of two C-reactive protein homologues from cod (Gadus morhua L.) serum

A review of soluble factors and receptors involved in fish skin immunity: The tip of the iceberg

The immune system of fish possesses soluble factors, receptors, pathways and cells very similar to those of the other vertebrates' immune system. Throughout evolutionary history, the exocrine secretions of organisms have accumulated a large reservoir of soluble factors that serve to protect organisms from microbial pathogens that could disrupt mucosal barrier homeostasis. In parallel, a diverse set of recognition molecules have been discovered that alert the organism to the presence of pathogens. The known functions of both the soluble factors and receptors mentioned above encompass critical aspects of host defense, such as pathogen binding and neutralization, opsonization, or modulation of inflammation if present. The molecules and receptors cooperate and are able to initiate the most appropriate immune response in an attempt to eliminate pathogens before host infection can begin. Furthermore, these recognition molecules, working in coordination with soluble defence factors, collaboratively erect a robust and perfectly coordinated defence system with complementary specificity, activity and tissue distribution. This intricate network constitutes an immensely effective defence mechanism for fish. In this context, the present review focuses on some of the main soluble factors and recognition molecules studied in the last decade in the skin mucosa of teleost fish. However, knowledge of these molecules is still very limited in all teleosts. Therefore, further studies are suggested throughout the review that would help to better understand the functions in which the proteins studied are involved.

Serum amyloid P-component/C-reactive proteins in fugu (Takifugu rubripes) egg with binding ability to disease-causing bacteria by carbohydrate-recognition

Two galactose-binding proteins were purified from the eggs of Takifugu rubripes by affinity chromatography. These proteins were detected at 26 and 23 kDa under reducing and at 40 and 45 kDa under non-reducing conditions at SDS-PAGE. The peptide sequences from both proteins matched to short-type pentraxin. The 26-kDa lectin was glycosylated, while the other one was not, indicating that these could be glycoforms of pentraxin. Messenger RNA of pentraxin was detected in eggs and embryos at 1-cell stage, was undetectable till blastula, and finally detected again after gastrula, suggesting that the mRNAs in eggs and 1-cell embryos were maternal in origin, and autologous transcription of the gene occurred after blastula. Since they bind to pathogenic bacteria, egg pentraxins may have immunological functions during embryogenesis. This is the first study to show the presence of short-type pentraxin in fish eggs and the diversity of fish egg lectins.

Post-translational protein deimination signatures and extracellular vesicles (EVs) in the Atlantic horseshoe crab (Limulus polyphemus)

The horseshoe crab is a living fossil and a species of marine arthropod with unusual immune system properties which are also exploited commercially. Given its ancient status dating to the Ordovician period (450 million years ago), its standing in phylogeny and unusual immunological characteristics, the horseshoe crab may hold valuable information for comparative immunology studies. Peptidylarginine deiminases (PADs) are calcium dependent enzymes that are phylogenetically conserved and cause protein deimination via conversion of arginine to citrulline. This post-translational modification can lead to structural and functional protein changes contributing to protein moonlighting in health and disease. PAD-mediated regulation of extracellular vesicle (EV) release, a critical component of cellular communication, has furthermore been identified to be a phylogenetically conserved mechanism. PADs, protein deimination and EVs have hitherto not been studied in the horseshoe crab and were assessed in the current study. Horseshoe crab haemolymph serum-EVs were found to be a poly-dispersed population in the 20-400 nm size range, with the majority of EVs falling within 40-123 nm. Key immune proteins were identified to be post-translationally deiminated in horseshoe crab haemolymph serum, providing insights into protein moonlighting function of Limulus and phylogenetically conserved immune proteins. KEGG (Kyoto encyclopaedia of genes and genomes) and GO (gene ontology) enrichment analysis of deiminated proteins identified in Limulus revealed KEGG pathways relating to complement and coagulation pathways, Staphylococcus aureus infection, glycolysis/gluconeogenesis and carbon metabolism, while GO pathways of biological and molecular pathways related to a range of immune and metabolic functions, as well as developmental processes. The characterisation of EVs, and post-translational deimination signatures, revealed here in horseshoe crab, contributes to current understanding of protein moonlighting functions and EV-mediated communication in this ancient arthropod and throughout phylogeny.

Local immune depression in Baltic cod (Gadus morhua) liver infected with Contracaecum osculatum

Third-stage larvae of the anisakid nematode Contracaecum osculatum infecting cod (Gadus morhua) liver elicit a host immune response involving both innate and adaptive factors, but the reactions differ between liver and spleen. Inflammatory reactions occur in both liver and spleen, but a series of immune effector genes are downregulated in liver infected with nematodes whereas these genes in spleen from the same fish are upregulated. A series of novel primer and probe sets targeting cod immune responses were developed and applied in a real-time quantitative polymerase chain reaction set-up to measure the expression of immune-relevant genes in liver and spleen of infected and uninfected cod. In infected liver, 12 of 23 genes were regulated. Genes encoding cytokines associated with inflammatory reactions (IL-1β, IL-6, IL-8) were significantly upregulated, whereas genes encoding effector molecules, assisting the elimination of pathogens, C-reactive protein (CRP)-PII, hepcidin, lysozyme G1, lysozyme G2, C3 and IgDm, were significantly downregulated. The number of downregulated genes increased with the parasite burden. In spleen, 14 of 23 immune genes showed significant regulation and nine of these were upregulated, including genes encoding CRPI, CRPII, C3, hepcidin and transferrin. The general gene expression level was higher in spleen compared to liver, and although inflammation was induced in nematode-infected liver, the effector molecule genes were depressed, which suggests a worm-induced immune suppression locally in the liver.

Extracellular vesicles from cod (Gadus morhua L.) mucus contain innate immune factors and deiminated protein cargo

Extracellular vesicles are released from cells and participate in cell communication via transfer of protein and genetic cargo derived from the parent cells. EVs play roles in normal physiology and immunity and are also linked to various pathological processes. Peptidylarginine deiminases (PADs) are phylogenetically conserved enzymes with physiological and pathophysiological roles. PADs cause post-translational protein deimination, resulting in structural and, in some cases, functional changes in target proteins and are also linked to EV biogenesis. This study describes for the first time EVs isolated from cod mucosa. Mucosal EVs were characterised by electron microscopy, nanoparticle tracking analysis and EV-specific surface markers. Cod mucosal EVs were found to carry PAD, complement component C3 and C-reactive proteins. C3 was found to be deiminated in both whole mucus and mucosal EVs, with some differences, and further 6 deiminated immune and cytoskeletal proteins were identified in EVs by LC-MS/MS analysis. As mucosal surfaces of teleost fish reflect human mucosal surfaces, these findings may provide useful insights into roles of EVs in mucosal immunity throughout phylogeny.

Evolution of C-Reactive Protein

C-reactive protein (CRP) is an evolutionarily conserved protein. From arthropods to humans, CRP has been found in every organism where the presence of CRP has been sought. Human CRP is a pentamer made up of five identical subunits which binds to phosphocholine (PCh) in a Ca²⁺-dependent manner. In various species, we define a protein as CRP if it has any two of the following three characteristics: First, it is a cyclic oligomer of almost identical subunits of molecular weight 20–30 kDa. Second, it binds to PCh in a Ca²⁺-dependent manner. Third, it exhibits immunological cross-reactivity with human CRP. In the arthropod horseshoe crab, CRP is a constitutively expressed protein, while in humans, CRP is an acute phase plasma protein and a component of the acute phase response. As the nature of CRP gene expression evolved from a constitutively expressed protein in arthropods to an acute phase protein in humans, the definition of CRP became distinctive. In humans, CRP can be distinguished from other homologous proteins such as serum amyloid P, but this is not the case for most other vertebrates and invertebrates. Literature indicates that the binding ability of CRP to PCh is less relevant than its binding to other ligands. Human CRP displays structure-based ligand-binding specificities, but it is not known if that is true for invertebrate CRP. During evolution, changes in the intrachain disulfide and interchain disulfide bonds and changes in the glycosylation status of CRP may be responsible for different structure-function relationships of CRP in various species. More studies of invertebrate CRP are needed to understand the reasons behind such evolution of CRP. Also, CRP evolved as a component of and along with the development of the immune system. It is important to understand the biology of ancient CRP molecules because the knowledge could be useful for immunodeficient individuals.

Biomimetic Polymer-Based Method for Selective Capture of C-Reactive Protein in Biological Fluids

Selective capturing and purification of C-reactive protein (CRP) from complex biological fluids plays a pivotal role in studying biological activities of CRP in various diseases. However, obvious nonspecific adsorption of proteins was observed on current affinity sorbents, and thus additional purification steps are often required, which could compromise the recovery of the target protein and/or introduce new impurities. In this study, inspired by the highly specific interaction between CRP and the cell membrane, an excellent anti-biofouling compound 2-(methacryloyloxy)ethyl phosphorylcholine and a highly hydrophilic crosslinker N, N'-methylenebisacrylamide were employed to fabricate a novel cell membrane biomimetic polymer for selective capture of CRP in the presence of calcium ions. Based on the polymer described above, a facile enrichment approach was established after systematic optimization of the washing and elution conditions. With its favorable properties, such as good porosity, weak electrostatic interaction, high hydrophilicity, and biocompatibility, the novel biomimetic polymer exhibits good specificity, selectivity, recovery (near 100%), purity (95%), and a lower nonspecific protein adsorption for CRP in comparison with commercial immobilized p-aminophenyl phosphoryl choline gel and other purification materials. Furthermore, the structural integrity and functionality of CRP in the elution fraction were well preserved and confirmed by circular dichroism spectroscopy, fluorescence spectroscopy, and immunoturbidimetric assay. Finally, the biomimetic polymer was successfully applied to the selective enrichment of CRP from sera of patients with inflammation and rats. The proposed novel enrichment approach based on the versatile biomimetic polymer can be used for effective CRP purification, which will benefit the in-depth study of its biological roles.

Pentraxins CRP-I and CRP-II are post-translationally deiminated and differ in tissue specificity in cod (Gadus morhua L.) ontogeny

Pentraxins are fluid phase pattern recognition molecules that form an important part of the innate immune defence and are conserved between fish and human. In Atlantic cod (Gadus morhua L.), two pentraxin-like proteins have been described, CRP-I and CRP-II. Here we show for the first time that these two CRP forms are post-translationally deiminated (an irreversible conversion of arginine to citrulline) and differ with respect to tissue specific localisation in cod ontogeny from 3 to 84 days post hatching. While both forms are expressed in liver, albeit at temporally differing levels, CRP-I shows a strong association with nervous tissue while CRP-II is strongly associated to mucosal tissues of gut and skin. This indicates differing roles for the two pentraxin types in immune responses and tissue remodelling, also elucidating novel roles for CRP-I in the nervous system. The presence of deimination positive bands for cod CRPs varied somewhat between mucus and serum, possibly facilitating CRP protein moonlighting, allowing the same protein to exhibit a range of biological functions and thus meeting different functional requirements in different tissues. The presented findings may further current understanding of the diverse roles of pentraxins in teleost immune defences and tissue remodelling, as well as in various human pathologies, including autoimmune diseases, amyloidosis and cancer.

Phylogeny and expression analysis of C-reactive protein (CRP) and serum amyloid-P (SAP) like genes reveal two distinct groups in fish

The acute phase response (APR) is an early innate immune function that is initiated by inflammatory signals, leading to the release of acute phase proteins to the bloodstream to re-establish homeostasis following microbial infection. In this study we analysed the Atlantic salmon (Salmo salar) whole-genome database and identified five C-reactive protein (CRP)/serum amyloid P component (SAP) like molecules namely CRP/SAP-1a, CRP/SAP-1b, CRP/SAP-1c, CRP/SAP-2 and CRP/SAP-3. These CRP/SAP genes formed two distinct sub-families, a universal group (group I) present in all vertebrates and a fish/amphibian specific group (group II). Salmon CRP/SAP-1a, CRP/SAP-1b and CRP/SAP-1c and CRP/SAP-2 belong to the group I family whilst salmon CRP/SAP-3 is a member of group II. Gene expression analysis showed that the salmon CRP/SAP-1a as well as serum amyloid A-5 (SAA-5), one of the major acute phase proteins, were significantly up-regulated by recombinant cytokines (rIL-1β and rIFNγ) in primary head kidney cells whilst the other four CRP/SAPs remained refractory. Furthermore, SAA-5 was produced as the main acute phase protein (APP) in Atlantic salmon challenged with Aeromonas salmonicida (aroA(-) strain) whilst salmon CRP/SAPs remained unaltered. Overall, these data illustrate the potential different functions of expanded salmon CRP/SAPs to their mammalian homologues.

CsPTX1, a pentraxin of Cynoglossus semilaevis, is an innate immunity factor with antibacterial effects

Pentraxin 1 (PTX1) is a member of the pentraxin protein family, which plays important roles in the innate immunity of vertebrates. In fish, the biological function of PTX1 is essentially unknown. In this study, we examined the expression and function of a PTX homologue (CsPTX1) from the tongue sole, Cynoglossus semilaevis. CsPTX1 contains 223 amino acids and shares 49.3%-38.8% overall sequence identity with other known fish pentraxins. CsPTX1 is expressed in multiple tissues and is upregulated by bacterial and viral infection. CsPTX1 contains a pentraxin domain, which is known to bind extracellular antigens, and recombinant CsPTX1 (rCsPTX1) bound a wide range of Gram-positive and Gram-negative bacteria. rCsPTX1 also agglutinated all the bacteria tested in a Ca(2+)-dependent manner and the agglutinating capacity of rCsPTX1 was abolished in the absence of calcium. As well as its ability to agglutinate bacterial cells, rCsPTX1 displayed apparent bacteriostatic activity against Pseudomonas fluorescens in vitro by influencing the permeability of the microbial envelope. When introduced in vivo, rCsPTX1 enhanced the host's resistance to bacterial infection. These results indicate that CsPTX1 is a classic pattern recognition molecule that defends C. semilaevis against bacterial infection.

Identification of a C-reactive protein like homologue from black rockfish (Sebastes schlegelii) evidencing its potent anti-microbial properties at molecular level

Pentraxins are a family of evolutionary conserved proteins that contains two main members, namely c-reactive proteins (CRPs) and serum amyloid P (SAP), which are involved in acute phase responses in animals. In this study, a cDNA sequence of a CRP-like molecule was identified from a previously constructed black rockfish cDNA database (RfCRP) and subsequently characterized at its molecular level. The complete coding region of RfCRP is 672 bp in length, and encodes a protein containing 224 amino acids with a predicted molecular mass of 25.19 kDa. Analysis of its derived amino acid sequence enabled typical features of pentraxin family members to be identified, including the pentraxin family signature in RfCRP. Results from multiple sequence alignment suggest the conservation of functionally important residues in RfCRP. According to the phylogenetic reconstruction that was generated using different pentraxin counterparts from different taxa, RfCRP shares a common vertebrate ancestral origin and most closely clusters with marine teleostan CRP. Furthermore, recombinant RfCRP demonstrated Ca(2+)-dependent agglutination activity against Escherichia coli, which could be completely inhibited in the presence of carbohydrate based ligands. Moreover, recombinant RfCRP also exhibited anti-bacterial activity against both E. coli and Streptococcus iniae. In addition, qPCR analysis indicated that RfCRP is ubiquitously expressed in physiologically important tissues, with pronounced expression in the spleen. After healthy fish were treated with polysaccharides or live S. iniae, basal expression of RfCRP was significantly upregulated in spleen and head kidney tissues. Collectively, our results suggest that RfCRP may be important in host anti-bacterial defense, and it might potentially participate in the acute phase of infection.

Yersiniosis in Atlantic cod, Gadus morhua (L.), characterization of the infective strain and host reactions

A disease outbreak in farmed Atlantic cod caused by Yersinia ruckeri is reported. Mortality started following vaccination of cod reared in two tanks (A and B). The accumulated mortality reached 1.9% in A and 4.8% in B in the following 30 days when treatment with oxytetracycline was applied. Biochemical and molecular analysis of Y. ruckeri isolates from the cod and other fish species from fresh and marine waters in Iceland revealed a high salinity-tolerant subgroup of Y. ruckeri serotype O1. Infected fish showed clinical signs comparable with those of Y. ruckeri -infected salmonids, with the exception of granuloma formations in infected cod tissues, which is a known response of cod to bacterial infections. Immunohistological examination showed Y. ruckeri antigens in the core of granulomas and the involvement of immune parameters that indicates a strong association between complement and lysozyme killing of bacteria. Experimental infection of cod with a cod isolate induced disease, and the calculated LD50 was 1.7 × 10(4) CFU per fish. The results suggest that yersiniosis can be spread between populations of freshwater and marine fish. Treatment of infected cod with antibiotic did not eliminate the infection, which can be explained by the immune response of cod producing prolonged granulomatous infection.

Influence of the cholinergic system on the immune response of teleost fishes: potential model in biomedical research

Fishes are the phylogenetically oldest vertebrate group, which includes more than one-half of the vertebrates on the planet; additionally, many species have ecological and economic importance. Fish are the first evolved group of organisms with adaptive immune mechanisms; consequently, they are an important link in the evolution of the immune system, thus a potential model for understanding the mechanisms of immunoregulation. Currently, the influence of the neurotransmitter acetylcholine (ACh) on the cells of the immune system is widely studied in mammalian models, which have provided evidence on ACh production by immune cells (the noncholinergic neuronal system); however, these neuroimmunomodulation mechanisms in fish and lower vertebrates are poorly studied. Therefore, the objective of this review paper was to analyze the influence of the cholinergic system on the immune response of teleost fish, which could provide information concerning the possibility of bidirectional communication between the nervous and immune systems in these organisms and provide data for a better understanding of basic issues in neuroimmunology in lower vertebrates, such as bony fishes. Thus, the use of fish as a model in biomedical research may contribute to a better understanding of human diseases and diseases in other animals.

Immuno-histochemical determination of humoral immune markers within bacterial induced granuloma formation in Atlantic cod (Gadus morhua L.)

In this study the involvement of several humoral immune parameters of Atlantic cod (Gadus morhua L.) were studied in granuloma formed as a result of infection by Aeromonas salmonicida ssp. achomogenes. The results showed a clear association of immune parameters within the granuloma, in particular the localization of complement component C3, and including evidence for the presence of IgM, APoLP-A1 (Apolipoprotein), CRP-PI and CRP-PII (pentraxin).

The C-reactive protein of tongue sole Cynoglossus semilaevis is an acute phase protein that interacts with bacterial pathogens and stimulates the antibacterial activity of peripheral blood leukocytes

Pentraxins are a family of evolutionarily conserved proteins that play an important part in innate immunity. C-reactive protein (CRP) is a member of the pentraxin family and in humans is known to be the major acute phase protein. In this work, we report the identification and analysis of a CRP, CsCRP, from half-smooth tongue sole (Cynoglossus semilaevis). CsCRP is composed of 228 amino acid residues and possesses a Pentraxin/CRP domain. Expression of CsCRP occurred in a wide range of tissues and was upregulated by pathogen infection in kidney, spleen, blood, and, in particular, liver. Following bacterial infection, CsCRP level in blood rose rapidly within 12 h and was approximately 3.8 fold of that of the basal level. Purified recombinant CsCRP (rCsCRP) was able to interact with Gram-negative and Gram-positive bacteria including those of pathogenic nature in a dose-dependent manner. When peripheral blood leukocytes (PBL) were infected with bacterial pathogen in the presence of rCsCRP, the respiratory burst and phagocytic capacity of the cells were increased to significant extents. Taken together, these results indicate that CsCRP is an acute phase protein that plays a role in innate immune defense against bacterial infection.

Hepatic transcriptome analysis of inter-family variability in flesh n-3 long-chain polyunsaturated fatty acid content in Atlantic salmon

Background

Genetic selection of Atlantic salmon families better adapted to alternative feed formulations containing high levels of vegetable ingredients has been suggested to ensure sustainable growth of aquaculture. The present study aimed to identify molecular pathways that could underlie phenotypic differences in flesh n-3 long-chain polyunsaturated fatty acid (LC-PUFA) levels when fish are fed vegetable oil diets. Liver transcriptome was analyzed and compared in four families presenting higher or lower n-3 LC-PUFA contents at two contrasting flesh total lipid levels.

Results

The main effect of n-3 LC-PUFA contents was in the expression of immune response genes (38% of all significantly affected genes), broadly implicated in the modulation of inflammatory processes and innate immune response. Although genetic evaluations of traits used in the breeding program revealed that the chosen families were not balanced for viral disease resistance, this did not fully explain the preponderance of immune response genes in the transcriptomic analysis. Employing stringent statistical analysis no lipid metabolism genes were detected as being significantly altered in liver when comparing families with high and low n-3 LC-PUFA flesh contents. However, relaxing the statistical analysis enabled identification of potentially relevant effects, further studied by RT-qPCR, in cholesterol biosynthesis, lipoprotein metabolism and lipid transport, as well as eicosanoid metabolism particularly affecting the lipoxygenase pathway. Total lipid level in flesh also showed an important effect on immune response and 8% of significantly affected genes related to lipid metabolism, including a fatty acyl elongase (elovl2), an acyl carrier protein and stearoyl-CoA desaturase.

Conclusions

Inter-family differences in n-3 LC-PUFA content could not be related to effects on lipid metabolism, including transcriptional modulation of the LC-PUFA biosynthesis pathway. An association was found between flesh adiposity and n-3 LC-PUFA in regulation of cholesterol biosynthesis, which was most likely explained by variation in tissue n-3 LC-PUFA levels regulating transcription of cholesterol metabolism genes through srebp2. A preponderance of immune response genes significantly affected by n-3 LC-PUFA contents could be potentially associated with disease resistance, possibly involving anti-inflammatory actions of tissue n-3 LC-PUFA through eicosanoid metabolism. This association may have been fortuitous, but it is important to clarify if this trait is included in future salmon breeding programmes.

Immune system and immune responses in fish and their role in comparative immunity study: a model for higher organisms

The basal position of fish in vertebrate phylogeny makes them very attractive for genomic and functional comparative immunity studies. Adaptive immunity arose early in vertebrate evolution, 450 million years ago between the divergence of cyclostomes and cartilaginous fish. The fundamental immune molecules, which include Ag-recognizing lymphocytes, immunoglobulins (Abs and Ig-family TCR), MHC products, and recombination-activating (RAG) 1 and 2 genes and the recombination mechanisms (cause of diversity in TCRs and Igs) are similar in fish and mammals. These molecules and their immune response mechanisms unravelled the primordial vertebrate immune system repertoire and adaptive radiations. Moreover, screening of animal models like zebrafish has a great importance to discover genes involved in T cell development, thymic organogenesis, and in immunity to infections. The zebrafish model may also be useful for cancer research due to its various features like rapid development, tractable genetics, ease in in vivo imaging and chemical screening.

The acute phase response of cod (Gadus morhua L.): expression of immune response genes

An acute phase response (APR) was experimentally induced in Atlantic cod (Gadus morhua L.) by intramuscular injection of turpentine oil. The change in the expression of immune related genes was monitored in the anterior kidney and the spleen over a period of 7 days. The genes examined were two types of pentraxins, apolipoprotein A1 (ApoA-I), the complement component C3, interleukin-1β (IL-1β), transferrin, cathelicidin, and hepcidin. All genes were constitutively expressed in both organs and their expression amplified by the turpentine injection. A pattern of response was observed both with respect to the organ preference and to the timing of a maximum response. The increased gene expression of the pentraxins, ApoA-I and C3 was restricted to the anterior kidney, the gene expression of IL-1β, cathelicidin, and transferrin increased in both organs, while hepcidin gene expression was only significantly increased in the spleen. The pentraxins and ApoA-I appear to be early mediators of APR in cod, possibly stimulating C3 and IL-1β response, while the antimicrobial peptides may play a minor role. The increase in transferrin gene expression in both organs, and apparent indifference to cortisol release associated with the turpentine injection, suggests that this could be a typical acute phase protein in cod.

The acute phase response of Atlantic cod (Gadus morhua): humoral and cellular response

Intra-muscular injection of turpentine oil was used to induce acute phase response (APR) in Atlantic cod (Gadus morhua L.). The effects on the serum cortisol, total protein, IgM and pentraxin concentration were examined as well as the effects on natural antibody, anti-trypsin and leukocyte respiratory burst activity. The turpentine injection resulted in a 26 fold increase in the cortisol level after 72 h. Slightly reduced serum protein level in both groups was attributed to the restricted feeding during the experimental period. The IgM serum concentration was significantly reduced after 168 h in the turpentine treated fish while the natural antibody activity was not affected. The anti-trypsin activity was initially suppressed but recovered to normal levels at the end of the experiment. The turpentine injection had little effect on the serum level of the pentraxins, CRP-PI and CRP-PII. The respiratory burst activity was significantly suppressed after 72 h. It is concluded that 1) cod shows a relatively slow humoral and cellular response to APR induction, 2) the increase in serum cortisol level may be the key modulator of the mainly suppressive effects on the immune parameters and 3) pentraxins are not typical acute phase proteins in cod.

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.