Nonspecific cytotoxic cells of teleosts are armed with multiple granzymes and other components of the granule exocytosis pathway

Novel C-type lectin mediated non-specific cytotoxic cells killing activity through NCCRP-1 in nile tilapia (Oreochromis niloticus)

Non-specific cytotoxic cells (NCCs) are vital immune cells involved in teleost's non-specific immunity. As a receptor molecule on the NCCs' surface, the non-specific cytotoxic cell receptor protein 1 (NCCRP-1) is known to play a crucial role in mediating their activity. Nevertheless, there have been limited studies on the signal molecule that transmits signals via NCCRP-1. In this study, a yeast two-hybrid (Y2H) library of tilapia liver and head kidney was constructed and subsequently screened with the bait vector NCCRP-1 of Oreochromis niloticus (On-NCCRP-1) to obtain a C-type lectin (On-CTL) with an interacting protein sequence. Consequently, the full-length sequence of On-CTL was cloned and analyzed. The expression analysis revealed that On-CTL is highly expressed in the liver and is widely distributed in other tissues. Furthermore, On-CTL expression was significantly up-regulated in the brain, intestine, and head kidney following a challenge with Streptococcus agalactiae. A point-to-point Y2H method was also used to confirm the binding between On-NCCRP-1 and On-CTL. The recombinant On-CTL (rOn-CTL) protein was purified. In vitro experiments demonstrated that rOn-CTL can up-regulate the expression of killer effector molecules in NCCs via its interaction with On-NCCRP-1. Moreover, activation of NCCs by rOn-CTL resulted in a remarkable enhancement in their ability to eliminate fathead minnow cells, indicating that rOn-CTL effectively modulates the killing activity of NCCs through the NCC receptor molecule On-NCCRP-1. These findings significantly contribute to our comprehension of the regulatory mechanisms governing NCC activity, paving the way for future research in this field.

Molecular characteristics and functional analysis of non-specific cytotoxic cell receptor (NCCRP1) in golden pompano (Trachinotus ovatus)

Non-specific cytotoxic cells (NCCs) are cytotoxic cell population found in innate immune system of teleost, playing crucial role in immune defense. Non-specific cytotoxic cell receptor protein 1 (NCCRP1) is responsible for recognizing target cells and activating NCCs. That said, since the studies regarding NCCs' role in fish during pathogen infection are few, it is necessary to conduct more comprehensive studies. In this study, we identified NCCRP1 from Trachinotus ovatus (ToNCCRP1). The open reading frame of ToNCCRP1 was found to be 702 bp, encoding a protein of 233 amino acids. Additionally, ToNCCRP1 contained a conserved F-box-associated domain and exhibited more than 61 % similarity to NCCRP1 in other fish species. Quantitative real-time PCR analysis showed that ToNCCRP1 mRNA was generally expressed in all tissues, with the highest level expressed in the liver. Furthermore, the expression of ToNCCRP1 was significantly upregulated following infection with Streptococcus iniae. In vitro experiments demonstrated that recombinant ToNCCRP1 possessed bacterial agglutination and binding capabilities, suggesting its antibacterial function. Additionally, we investigated the immune response of head kidney leukocytes (HKLs) to ToNCCRP1. The challenge experiments revealed that ToNCCRP1 played a role in the immune response by influencing the inflammatory response, regulating signaling pathways and apoptosis in HKLs. These findings suggest that NCCRP1 is involved in the immune defense against pathogenic infections in golden pompano, providing insights into the immune mechanisms of teleost.

Extended Cleavage Specificity of two Hematopoietic Serine Proteases from a Ray-Finned Fish, the Spotted Gar (Lepisosteus oculatus)

The extended cleavage specificities of two hematopoietic serine proteases originating from the ray-finned fish, the spotted gar (Lepisosteus oculatus), have been characterized using substrate phage display. The preference for particular amino acids at and surrounding the cleavage site was further validated using a panel of recombinant substrates. For one of the enzymes, the gar granzyme G, a strict preference for the aromatic amino acid Tyr was observed at the cleavable P1 position. Using a set of recombinant substrates showed that the gar granzyme G had a high selectivity for Tyr but a lower activity for cleaving after Phe but not after Trp. Instead, the second enzyme, gar DDN1, showed a high preference for Leu in the P1 position of substrates. This latter enzyme also showed a high preference for Pro in the P2 position and Arg in both P4 and P5 positions. The selectivity for the two Arg residues in positions P4 and P5 suggests a highly specific substrate selectivity of this enzyme. The screening of the gar proteome with the consensus sequences obtained by substrate phage display for these two proteases resulted in a very diverse set of potential targets. Due to this diversity, a clear candidate for a specific immune function of these two enzymes cannot yet be identified. Antisera developed against the recombinant gar enzymes were used to study their tissue distribution. Tissue sections from juvenile fish showed the expression of both proteases in cells in Peyer's patch-like structures in the intestinal region, indicating they may be expressed in T or NK cells. However, due to the lack of antibodies to specific surface markers in the gar, it has not been possible to specify the exact cellular origin. A marked difference in abundance was observed for the two proteases where gar DDN1 was expressed at higher levels than gar granzyme G. However, both appear to be expressed in the same or similar cells, having a lymphocyte-like appearance.

The Extended Cleavage Specificity of Channel Catfish Granzyme-like II, A Highly Specific Elastase, Expressed by Natural Killer-like Cells

The extended cleavage specificity of catfish granzyme-like II has been characterized using substrate phage display. The preference for particular amino acids at and surrounding the cleavage site was further validated by using a panel of recombinant substrates. This serine protease, which has previously been isolated as cDNA from a catfish natural killer-like cell line showed a preference for Ala in the P1 position of the substrate, and for multiple basic amino acids N-terminally of the cleavage site. A closely related zebrafish serine protease (zebrafish esterase-like) showed a very similar cleavage specificity, indicating an evolutionary conservation of this protease specificity among various fish species. Two catfish serine proteases, originating from NK-like cells, have now been isolated and characterized. One of them is highly specific met-ase with similar characteristics as the mammalian granzyme M. This enzyme may be involved in the induction of apoptosis in virus-infected cells, with a potential target in (catfish) caspase 6. In contrast to catfish granzyme-like I, the second enzyme analyzed here does not seem to have a direct counterpart in mammalian NK cells, and its role in the immune function of catfish NK cells is, therefore, still not known. However, this enzyme seems to be able to cleave a number of cytoskeletal proteins, indicating a separate strategy to induce apoptosis in target cells. Both of these enzymes are very interesting targets for further studies of their roles in catfish immunity, as enzymes with similar specificities have also been identified in zebrafish.

Two granzyme A/K homologs in Zebra mbuna have different specificities, one classical tryptase and one with chymase activity

Granzymes A and K are two highly homologous serine proteases expressed by mammalian cytotoxic T cells (CTLs) and natural killer (NK) cells. The locus encoding these two proteases is the first of the hematopoietic serine protease loci to appear during vertebrate evolution. This locus is found in all jawed vertebrates including the cartilaginous fishes. Granzyme A is the most abundant of the different granzymes expressed by CTLs and NK cells and its potential function has been studied extensively for many years. However, no clear conclusions concerning its primary role in the immune defense has been obtained. In all mammals, there are only one copy each of granzyme A and K, whereas additional copies are found in both cartilaginous and ray finned fishes. In cichlids two of these copies seem to encode new members of the granzyme A/K family. These two new members appear to have changed primary specificity and to be pure chymases based on the amino acids in their active site substrate binding pockets. Interestingly, one of these gene copies is located in the middle of the granzyme A/K locus, while the other copy is present in another locus, the met-ase locus. We here present a detailed characterization of the extended cleavage specificity of one of these non-classical granzymes, a Zebra mbuna granzyme positioned in the granzyme A/K locus. This enzyme, named granzyme A2, showed a high preference for tyrosine in the P1 position of substrates, thereby being a strict chymase. We have also characterized one of the classical granzyme A/Ks of the Zebra mbuna, granzyme A1, which is a tryptase with preference for arginine in the P1 position of substrates. Based on their extended specificities, the two granzymes showed major similarities, but also some differences in preferred amino acids in positions surrounding the cleavable amino acid. Fish lack one of the hematopoietic serine protease loci of mammals, the chymase locus, where one of the major mast cell enzymes is located. An interesting question is now if cichlids have by compensatory mechanisms generated a mast cell chymase from another locus, and if similar chymotryptic enzymes have appeared also in other fish species.

Expression changes of non-specific cytotoxic cell receptor (NCCRP1) and proliferation and migration of NCCs post-Nocardia seriolae infection in Northern Snakehead

Non-specific cytotoxic cells (NCCs) are essential to the cytotoxic cell-mediated immune response in teleost. The fish non-specific cytotoxic cell receptor protein 1 (NCCRP1) plays an important role as a membrane protein in the recognition of target cells and the activation of NCC. However, the roles of fish NCCs during pathogen infection require comprehensive studies. In this study, the coding sequence of northern snakehead (Channa argus) nccrp1 (Canccrp1) was cloned. Canccrp1 contains an open reading frame of 690 bp, encoding a peptide of 229 amino acids with a conserved F-box-associated domain (FBA) and proline-rich motifs (PRMs). Transcriptional expression analysis revealed that the constitutive expression of Canccrp1 was higher in the immune-related organs, such as liver, kidneys, and spleen. Moreover, mRNA and protein expression of Canccrp1 gradually increased in the spleen at 1-6 days post infection (dpi) with Nocardia seriolae, in addition to reaching peak expression in both the kidneys and liver at 2 dpi. A polyclonal antibody prepared against recombinant CaNCCRP1 effectively labeled NCCs in peripheral blood and different tissues. Then, immunofluorescence (IF) staining showed that the number of NCCs was significantly increased and showed a scattered distribution in the early stages of N. seriolae infection (2 and 4 dpi) before the forming of granulomas. At the late stages of N. seriolae infection (6 dpi), more NCCs migrated to preexisting granulomas, showing significant coaccumulation with N. seriolae. All these results clearly indicate the expression changes of CaNCCRP1, and the number and localization changes of NCCs post-N. seriolae infection, implying potential roles for fish NCCs in the antimicrobial infection process in fish.

Profile of Innate Immunity in Gilthead Seabream Larvae Reflects Mortality upon Betanodavirus Reassortant Infection and Replication

Historically, gilthead seabream (Sparus aurata) has been considered a fish species resistant to nervous necrosis virus (NNV) disease. Nevertheless, mortality in seabream hatcheries, associated with typical clinical signs of the viral encephalopathy and retinopathy (VER) disease has been confirmed to be caused by RGNNV/SJNNV reassortants. Because of this, seabream larvae at 37 and 86 days post-hatching (dph) were infected by immersion with RGNNV/SJNNV and SJNNV/RGNNV reassortants under laboratory conditions, and mortality, viral replication and immunity were evaluated. Our results show that gilthead seabream larvae, mainly those at 37 dph, are susceptible to infection with both NNV reassortant genotypes, with the highest impact from the RGNNV/SJNNV reassortant. In addition, viral replication occurs at both ages (37 and 86 dph) but the recovery of infective particles was only confirmed in 37 dph larvae,; this value was also highest with the RGNNV/SJNNV reassortant. Larvae immunity, including the expression of antiviral, inflammatory and cell-mediated cytotoxicity genes, was affected by NNV infection. Levels of the natural killer lysin (Nkl) peptide were increased in SJNNV/RGNNV-infected larvae of 37 dph, though hepcidin was not. Our results demonstrate that the seabream larvae are susceptible to both NNV reassortants, though mainly to RGNNV/SJNNV, in an age-dependent manner.

Summary and comparison of the perforin in teleosts and mammals: A review

Perforin, a pore-forming glycoprotein, has been demonstrated to play key roles in clearing virus-infected cells and tumour cells due to its ability of forming 'pores' on the cell membranes. Additionally, perforin is also found to be associated with human diseases such as tumours, virus infections, immune rejection and some autoimmune diseases. Until now, plenty of perforin genes have been identified in vertebrates, especially the mammals and teleost fish. Conversely, vertebrate homologue of perforin gene was not identified in the invertebrates. Although recently there have been several reviews focusing on perforin and granzymes in mammals, no one highlighted the current advances of perforin in the other vertebrates. Here, in addition to mammalian perforin, the structure, evolution, tissue distribution and function of perforin in bony fish are summarized, respectively, which will allow us to gain more insights into the perforin in lower animals and the evolution of this important pore-forming protein across vertebrates.

Biological characterisation, expression and functional analysis of non-specific cytotoxic cell receptor protein 1 in Nile tilapia (Oreochromis niloticus)

Non-specific cytotoxic cell receptor protein 1 (NCCRP-1) plays a role in recognition of target cell and activation of non-specific cytotoxic cell (NCC). In this study, the full length of Nile tilapia NCCRP-1 (On-NCCRP-1) was cloned. cDNA is composed of 1045 bp with a 90 bp of 5'-Untranslated Regions (UTR), 702 bp open reading frame (ORF) and 253 bp 3'-UTR, encoding 233 amino acids (GenBank accession no: MF162296). The On-NCCRP-1 genomic sequence is 4471 bp in length and contains six exons and five introns. On-NCCRP-1 possesses some inherent conservative domains, such as proline-rich motifs, antigen recognition site, and F-box-related domain. Subcellular localisation and Western blot analysis indicated that On-NCCRP-1 is located in the cell membrane. The transcript of On-NCCRP-1 was detected in all the examined tissues of healthy Nile tilapia by using qRT-PCR, with the highest expression levels in the liver. Following Streptococcus agalactiae challenged in vivo, the On-NCCRP-1 expression was up-regulated significantly in brain, intestines, head kidney and spleen. In the in vitro analysis, the On-NCCRP-1 expression in NCCs was up-regulated significantly from 8 h to 12 h after LPS challenge, and up-regulated significantly at 12 h after challenged with polyI:C. After NCCs were challenged with inactivated S. agalactiae, the On-NCCRP-1 expression was down-regulated significantly after 24 h. NF-кB pathway was strongly activated by the over-expression of On-NCCRP-1 in HEK-293T cells. These results indicate that On-NCCRP-1, as a membrane surface receptor of NCCs, may play an important role in immune response to pathogenic infection in Nile tilapia.

Teleost cytotoxic T cells

Cell-mediated cytotoxicity is one of the major mechanisms by which vertebrates control intracellular pathogens. Two cell types are the main players in this immune response, natural killer (NK) cells and cytotoxic T lymphocytes (CTL). While NK cells recognize altered target cells in a relatively unspecific manner CTLs use their T cell receptor to identify pathogen-specific peptides that are presented by major histocompatibility (MHC) class I molecules on the surface of infected cells. However, several other signals are needed to regulate cell-mediated cytotoxicity involving a complex network of cytokine- and ligand-receptor interactions. Since the first description of MHC class I molecules in teleosts during the early 90s of the last century a remarkable amount of information on teleost immune responses has been published. The corresponding studies describe teleost cells and molecules that are involved in CTL responses of higher vertebrates. These studies are backed by functional investigations on the killing activity of CTLs in a few teleost species. The present knowledge on teleost CTLs still leaves considerable room for further investigations on the mechanisms by which CTLs act. Nevertheless the information on teleost CTLs and their regulation might already be useful for the control of fish diseases by designing efficient vaccines against such diseases where CTL responses are known to be decisive for the elimination of the corresponding pathogen. This review summarizes the present knowledge on CTL regulation and functions in teleosts. In a special chapter, the role of CTLs in vaccination is discussed.

Fish Granzyme A Shows a Greater Role Than Granzyme B in Fish Innate Cell-Mediated Cytotoxicity

Granzymes (Gzm) are serine proteases, contained into the secretory granules of cytotoxic cells, responsible for the cell-mediated cytotoxicity (CMC) against tumor cells and intracellular pathogens such as virus and bacteria. In fish, they have received little attention to their existence, classification or functional characterization. Therefore, we aimed to identify and evaluate their functional and transcriptomic relevance in the innate CMC activity of two relevant teleost fish species, gilthead seabream and European sea bass. Afterwards, we wanted to focus on their regulation upon nodavirus (NNV) infection, a virus that causes great mortalities to sea bass specimens while seabream is resistant. In this study, we have identified genes encoding GzmA and GzmB in both seabream and sea bass, as well as GzmM in seabream, which showed good phylogenetic relation to their mammalian orthologs. In addition, we found enzymatic activity related to tryptase (GzmA and/or GzmK), aspartase (GzmB), metase (GzmM), or chymase (GzmH) in resting head-kidney leucocytes (HKLs), with the following order of activity: GzmA/K ~ GzmM >> GzmH >>> GzmB. In addition, during innate CMC assays consisting on HKLs exposed to either mock- or NNV-infected target cells, though all the granzyme transcripts were increased only the tryptase activity did. Thus, our data suggest a high functional activity of GzmA/K in the innate CMC and a marginal one for GzmB. Moreover, GzmB activity was detected into target cells during the CMC assays. However, the percentage of target cells with GzmB activity after the CMC assays was about 10-fold lower than the death target cells, demonstrating that GzmB is not the main inductor of cell death. Moreover, in in vivo infection with NNV, gzm transcription is differently regulated depending on the fish species, genes and tissues. However, the immunohistochemistry study revealed an increased number of GzmB stained cells and areas in the brain of seabream after NNV infection, which was mainly associated with the lesions detected. Further studies are needed to ascertain the molecular nature, biological function and implication of fish granzymes in the CMC activity, and in the antiviral defense in particular.

Acquired Protective Immunity in Atlantic Salmon Salmo salar against the Myxozoan Kudoa thyrsites Involves Induction of MHIIβ+ CD83+ Antigen-Presenting Cells

The histozoic myxozoan parasite Kudoa thyrsites causes postmortem myoliquefaction and is responsible for economic losses to salmon aquaculture in the Pacific Northwest. Despite its importance, little is known about the host-parasite relationship, including the host response to infection. The present work sought to characterize the immune response in Atlantic salmon during infection, recovery, and reexposure to K. thyrsites After exposure to infective seawater, infected and uninfected smolts were sampled three times over 4,275 degree-days. Histological analysis revealed infection severity decreased over time in exposed fish, while in controls there was no evidence of infection. Following a secondary exposure of all fish, severity of infection in the controls was similar to that measured in exposed fish at the first sampling time but was significantly reduced in reexposed fish, suggesting the acquisition of protective immunity. Using immunohistochemistry, we detected a population of MHIIβ+ cells in infected muscle that followed a pattern of abundance concordant with parasite prevalence. Infiltration of these cells into infected myocytes preceded destruction of the plasmodium and dissemination of myxospores. Dual labeling indicated a majority of these cells were CD83+/MHIIβ+ Using reverse transcription-quantitative PCR, we detected significant induction of cellular effectors, including macrophage/dendritic cells (mhii/cd83/mcsf), B cells (igm/igt), and cytotoxic T cells (cd8/nkl), in the musculature of infected fish. These data support a role for cellular effectors such as antigen-presenting cells (monocyte/macrophage and dendritic cells) along with B and T cells in the acquired protective immune response of Atlantic salmon against K. thyrsites.

Innate Cell-Mediated Cytotoxic Activity of European Sea Bass Leucocytes Against Nodavirus-Infected Cells: A Functional and RNA-seq Study

Nervous necrosis virus (NNV) causes high mortalities in several marine species. We aimed to evaluate the innate cell-mediated cytotoxic (CMC) activity of head-kidney leucocytes (HKLs) isolated from naïve European sea bass (Dicentrarchus labrax) and gilthead seabream (Sparus aurata), a very susceptible and resistant fish species to NNV, respectively, against fish cell lines infected with NNV. Seabream HKLs showed significantly increased innate CMC activity against NNV-infected cells, compared to those uninfected, while sea bass HKLs failed to do so. Thus, we performed a RNA-seq study to identify genes related to the CMC activity of sea bass leucocytes. Thus, we found that sea bass HKLs incubated with DLB-1 cells alone (CMC_DLB1) or with NNV-infected DLB-1 cells (CMC_DLB1-NNV) showed very similar transcriptomic profiles and the GO analysis revealed that most of the up-regulated genes were related to immunity. Strikingly, when the CMC samples with and without NNV were compared, GO analysis revealed that most of the up-regulated genes in CMC_DLB1-NNV samples were related to metabolism and very few to immunity. This is also in agreement with the functional data. These data point to the escape of CMC activity by NNV infection as an important factor involved in the high susceptibility to nodavirus infections of European sea bass.

Systems analysis uncovers inflammatory Th/Tc17-driven modules during acute GVHD in monkey and human T cells

One of the central challenges of transplantation is the development of alloreactivity despite the use of multiagent immunoprophylaxis. Effective control of this immune suppression-resistant T-cell activation represents one of the key unmet needs in the fields of both solid-organ and hematopoietic stem cell transplant (HCT). To address this unmet need, we have used a highly translational nonhuman primate (NHP) model to interrogate the transcriptional signature of T cells during breakthrough acute graft-versus-host disease (GVHD) that occurs in the setting of clinically relevant immune suppression and compared this to the hyperacute GVHD, which develops in unprophylaxed or suboptimally prophylaxed transplant recipients. Our results demonstrate the complex character of the alloreactivity that develops during ongoing immunoprophylaxis and identify 3 key transcriptional hallmarks of breakthrough acute GVHD that are not observed in hyperacute GVHD: (1) T-cell persistence rather than proliferation, (2) evidence for highly inflammatory transcriptional programming, and (3) skewing toward a T helper (Th)/T cytotoxic (Tc)17 transcriptional program. Importantly, the gene coexpression profiles from human HCT recipients who developed GVHD while on immunosuppressive prophylactic agents recapitulated the patterns observed in NHP, and demonstrated an evolution toward a more inflammatory signature as time posttransplant progressed. These results strongly implicate the evolution of both inflammatory and interleukin 17-based immune pathogenesis in GVHD, and provide the first map of this evolving process in primates in the setting of clinically relevant immunomodulation. This map represents a novel transcriptomic resource for further systems-based efforts to study the breakthrough alloresponse that occurs posttransplant despite immunoprophylaxis and to develop evidence-based strategies for effective treatment of this disease.

Channel catfish granzyme-like I is a highly specific serine protease with metase activity that is expressed by fish NK-like cells

Here we present the extended cleavage specificity of catfish granzyme-like I, previously identified in fish NK-like cells. This protease has been characterised using substrate phage display and further validated by using a panel of recombinant substrates. A strict preference for Met in the P1 (cleavage) position, indicating metase specificity was observed. A screening of potential in vivo substrates was performed based on the derived P5-P3' consensus: Arg-Val-Thr-Gly-Met(↓)Ser-Leu-Val. Channel catfish caspase 6 was one very interesting potential target identified. This site was present in an adjacent position to the classic caspase activation site (Asp179 in human caspase 6). Cleavage of this site (hence potential activation) by the catfish granzyme-like I could reveal a novel mechanism of caspase 6 activation. This poses an interesting idea that the role of granzyme-like proteases in the activation of caspase dependent apoptosis mechanisms has been conserved for over 400 million years.

Granule Associated Serine Proteases of Hematopoietic Cells - An Analysis of Their Appearance and Diversification during Vertebrate Evolution

Serine proteases are among the most abundant granule constituents of several hematopoietic cell lineages including mast cells, neutrophils, cytotoxic T cells and NK cells. These proteases are stored in their active form in the cytoplasmic granules and in mammals are encoded from four different chromosomal loci: the chymase locus, the met-ase locus, the T cell tryptase and the mast cell tryptase locus. In order to study their appearance during vertebrate evolution we have performed a bioinformatic analysis of related genes and gene loci from a large panel of metazoan animals from sea urchins to placental mammals for three of these loci: the chymase, met-ase and granzyme A/K loci. Genes related to mammalian granzymes A and K were the most well conserved and could be traced as far back to cartilaginous fish. Here, the granzyme A and K genes were found in essentially the same chromosomal location from sharks to humans. However in sharks, no genes clearly identifiable as members of the chymase or met-ase loci were found. A selection of these genes seemed to appear with bony fish, but sometimes in other loci. Genes related to mammalian met-ase locus genes were found in bony fish. Here, the most well conserved member was complement factor D. However, genes distantly related to the neutrophil proteases were also identified in this locus in several bony fish species, indicating that this locus is also old and appeared at the base of bony fish. In fish, a few of the chymase locus-related genes were found in a locus with bordering genes other than the mammalian chymase locus and some were found in the fish met-ase locus. This indicates that a convergent evolution rather than divergent evolution has resulted in chymase locus-related genes in bony fish.

Proinflammatory Caspase A Activation and an Antiviral State Are Induced by a Zebrafish Perforin after Possible Cellular and Functional Diversification from a Myeloid Ancestor

In mammals, perforins play a central role in the granule-dependent cell death induced by natural killer T cells and cytotoxic T lymphocytes, and participate both in the defense against virus-infected and neoplastic cells and in the recognition of nonself molecules by the immune system. Little is known about fish perforin genes. We examined the zebrafish with the aim of increasing our knowledge about the role of perforins. We characterized 6 perforin genes in the zebrafish genome, and we studied them at the evolutionary level in combination with expression patterns in several tissues and cell populations, during both larval development and in the course of a viral infection. Our results suggest the specialization of different cell types in the production of perforins. Moreover, functional diversification during the evolution of these molecules could be inferred from this study. In particular, one of the genes, prf19b, which is mainly produced by myeloid cells, seemed to be involved in antiviral defense, conferring protection after an in vivo infection.

Decreased levels of perforin-positive lymphocytes are associated with posttraumatic complications in patients with major trauma

OBJECTIVE

Posttraumatic immune disorder can cause complications including systemic inflammatory response syndrome (SIRS) and multiple-organ dysfunction syndrome (MODS). Cytotoxic granules containing perforin and granzyme-B (GrB) are released by cytotoxic CD8(+) T lymphocytes, NK and γδT cells after major trauma. This prospective clinical study was designed to analyze the association between these immune components and complications after major trauma.

METHODS

We retrospectively studied 48 patients aged between 16 and 65 years admitted within 90min of major trauma (Injury Severity Score>16) and surviving beyond 7 days, and 20 healthy controls. Blood samples were drawn on admission and after 1, 3 and 7 days. CD8(+) T, NK and γδT cell counts in peripheral blood and the levels of perforin and GrB in these cells were analyzed by flow cytometry. Clinical aspects of MODS and SIRS were recorded daily.

RESULTS

CD8(+) T cell counts were not significantly different in patients with SIRS or uncomplicated group, but were depressed in the MODS group after trauma. However, NK cell counts in patients with MODS were significantly depressed only at day 7 after injury, and γδT cell counts were significantly depressed after trauma. Perforin levels in CD8(+) T, NK and γδT cells in patients with MODS were depressed after trauma. GrB levels in NK, CD8(+) T and γδT cells in patients with MODS were significantly depressed at 3 and 7 days post trauma.

CONCLUSION

Posttraumatic MODS is associated with early, sustained, and severe depression of lymphocytes.

Molecular cloning of NCCRP-1 gene from orange-spotted grouper (Epinephelus coioides) and characterization of NCCRP-1(+) cells post Cryptocaryon irritans infection

Nonspecific cytotoxic cells (NCCs) are an important cytotoxic cell population in the innate teleost immune system. The receptor designated "NCC receptor protein 1" (NCCRP-1) has been reported to be involved in the recognition and activation of NCCs. In this study, the full-length cDNA of Epinephelus coioides NCCRP-1 (ecnccrp-1) was cloned. The open reading frame (ORF) of ecnccrp-1 is 699 bp, encoding a 232 amino acid protein that includes proline-rich motifs at the N-terminus and is related to the F-box associated family. Although a bioinformatics analysis showed that EcNCCRP-1 had no signal peptide or transmembrane helices, a polyclonal antibody directed against recombinant EcNCCRP-1 efficiently labeled a membrane protein in the head kidney, detected with Western blot analysis, which indicated that the protein localized to the cell surface. RT-PCR showed that the constitutive expression of ecnccrp-1 was higher in the lymphoid organs, such as the trunk kidney, spleen, head kidney, and thymus, and lower in brain, heart, fat, liver, muscle, and skin. After infection with Cryptocaryon irritans, the transcription of ecnccrp-1 was analyzed at the infected sites (skin and gills) and in the systemic immune organs (head kidney and spleen). At the infected sites, especially the skin, ecnccrp-1 expression was upregulated at 6h post infection, reaching peak expression on day 3 post the primary infection. However, the expression patterns differed in the systemic immune organs. In the spleen, ecnccrp-1 was gradually increased in the early infection period and decreased sharply on day 3 post the primary infection, whereas in the head kidney, the transcription of ecnccrp-1 was depressed during almost the whole course of infection. An immunohistochemical analysis showed that EcNCCRP-1(+) cells accumulated at the sites of infection with C. irritans. These results suggested that NCCs were involved in the process of C. irritans infection in E. coioides.

Granule proteases of hematopoietic cells, a family of versatile inflammatory mediators – an update on their cleavage specificity, in vivo substrates, and evolution

Cells from several of the hematopoietic cell lineages including mast cells, basophils, neutrophils, cytotoxic T cells, and natural killer (NK) cells store proteases at very high levels within their cytoplasmic granules. In mast cells, these proteases can account for up to 35% of the total cellular protein, and the absolute majority of these belong to the chymotrypsin-related serine protease family. A number of very diverse functions have been identified for these proteases, including apoptosis induction, blood pressure regulation, inactivation of insect and snake toxins, intestinal parasite expulsion, killing of bacteria and fungi, induction, mobilization, or degradation of cytokines, and the degradation of connective tissue components. A very broad spectrum of primary cleavage specificities has also been observed, including chymase, tryptase, asp-ase, elastase, and met-ase specificities, which highlights the large flexibility in the active site of these proteases. Mast cells primarily express chymases and tryptases with chymotryptic or tryptic primary cleavage specificities, respectively. Neutrophils have several enzymes with chymase, elastase, and tryptase specificities. T cells and NK cells express between 5 and 14 different granzymes, depending on the species, and these enzymes have tryptase, asp-ase, chymase, and met-ase specificities. This review focuses on the appearance of these proteases during vertebrate evolution, their primary and extended cleavage specificities, and their potential in vivo substrates. The in vivo substrates and functions are a particular challenging issue because several of these enzymes have a relatively broad specificity and may therefore cleave a wide range of different substrates.

Teleost T and NK cell immunity

The main function of the immune system is to maintain the organism's homeostasis when invaded by foreign material or organisms. Prior to successful elimination of the invader it is crucial to distinguish self from non-self. Most pathogens and altered cells can be recognized by immune cells through expressed pathogen- or danger-associated molecular patterns (PAMPS or DAMPS, respectively), through non-self (e.g. allogenic or xenogenic cells) or missing major histocompatibility (MHC) class I molecules (some virus-infected target cells), and by presenting foreign non-self peptides of intracellular (through MHC class I-e.g. virus-infected target cells) or extracellular (through MHC class II-e.g. from bacteria) origin. In order to eliminate invaders directly or by destroying their ability to replicate (e.g. virus-infected cells) specialized immune cells of the innate and adaptive responses appeared during evolution. The first line of defence is represented by the evolutionarily ancient macrophages and natural killer (NK) cells. These innate mechanisms are well developed in bony fish. Two types of NK cell homologues have been described in fish: non-specific cytotoxic cells and NK-like cells. Adaptive cell-mediated cytotoxicity (CMC) requires key molecules expressed on cytotoxic T lymphocytes (CTLs) and target cells. CTLs kill host cells harbouring intracellular pathogens by binding of their T cell receptor (TCR) and its co-receptor CD8 to a complex of MHC class I and bound peptide on the infected host cell. Alternatively, extracellular antigens are taken up by professional antigen presenting cells such as macrophages, dendritic cells and B cells to process those antigens and present the resulting peptides in association with MHC class II to CD4(+) T helper cells. During recent years, genes encoding MHC class I and II, TCR and its co-receptors CD8 and CD4 have been cloned in several fish species and antibodies have been developed to study protein expression in morphological and functional contexts. Functional assays for innate and adaptive lymphocyte responses have been developed in only a few fish species. This review summarizes and discusses recent results and developments in the field of T and NK cell responses with focus on economically important and experimental model fish species in the context of vaccination.

Atlantic salmon reovirus infection causes a CD8 T cell myocarditis in Atlantic salmon (Salmo salar L.)

Heart and skeletal inflammation (HSMI) of farmed Atlantic salmon (Salmo salar L.) is a disease characterized by a chronic myocarditis involving the epicardium and the compact and spongious part of the heart ventricle. Chronic myositis of the red skeletal muscle is also a typical finding of HSMI. Piscine reovirus (PRV) has been detected by real-time PCR from farmed and wild salmon with and without typical changes of HSMI and thus the causal relationship between presence of virus and the disease has not been fully determined. In this study we show that the Atlantic salmon reovirus (ASRV), identical to PRV, can be passaged in GF-1 cells and experimental challenge of naïve Atlantic salmon with cell culture passaged reovirus results in cardiac and skeletal muscle pathology typical of HSMI with onset of pathology from 6 weeks, peaking by 9 weeks post challenge. ASRV replicates in heart tissue and the peak level of virus replication coincides with peak of heart lesions. We further demonstrate mRNA transcript assessment and in situ characterization that challenged fish develop a CD8+ T cell myocarditis.

Fish T cells: recent advances through genomics

This brief review is intended to provide a concise overview of the current literature concerning T cells, advances in identifying distinct T cell functional subsets, and in distinguishing effector cells from memory cells. We compare and contrast a wealth of recent progress made in T cell immunology of teleost, elasmobranch, and agnathan fish, to knowledge derived from mammalian T cell studies. From genome studies, fish clearly have most components associated with T cell function and we can speculate on the presence of putative T cell subsets, and the ability to detect their differentiation to form memory cells. Some recombinant proteins for T cell associated cytokines and antibodies for T cell surface receptors have been generated that will facilitate studying the functional roles of teleost T cells during immune responses. Although there is still a long way to go, major advances have occurred in recent years for investigating T cell responses, thus phenotypic and functional characterization is on the near horizon.

Comparative study of tumorigenesis and tumor immunity in invertebrates and nonmammalian vertebrates

Despite intense study in mammals, the different roles played by the immune system in detecting (immunosurveillance), controlling and remodeling (immunoediting) neoplasia, and perhaps in metastasis are not fully understood. In this review, I will present evidence of neoplasia and invasive malignancy, as well as tumor immunity in invertebrates and nonmammalian vertebrates. I will also present a comparative and evolutionary view of the complex interactions between neoplasia and the host immune system. Overall, I wish to go beyond the too simplistic dichotomy between invertebrates with innate immunity that are only affected with benign neoplasia and vertebrates with adaptive immunity that are affected by metastatic malignancies or cancer.

The innate immune response of finfish--a review of current knowledge

The decline in the fisheries of traditional marine species has been an incentive for the diversification of today's aquaculture sector into the intensive rearing of many finfish species. The increasing interest in commercial farming of different finfish species is expected to result in similar environmental and husbandry-related problems as have been experienced in the development of the salmonid farming industry. An understanding of the biology of the fish species being cultured, in particular the immune response is important for improved husbandry and health management of the species. The innate immune system of fish has generated increasing interest in recent years and is now thought to be of key importance in primary defence and in driving adaptive immunity. This review focuses on key components (cellular and humoral) of the innate immune responses of different fish species of commercial importance.

Mast Cell Proteases

Mast cells (MCs) are traditionally thought of as a nuisance for its host, for example, by causing many of the symptoms associated with allergic reactions. In addition, recent research has put focus on MCs for displaying harmful effects during various autoimmune disorders. On the other hand, MCs can also be beneficial for its host, for example, by contributing to the defense against insults such as bacteria, parasites, and snake venom toxins. When the MC is challenged by an external stimulus, it may respond by degranulation. In this process, a number of powerful preformed inflammatory "mediators" are released, including cytokines, histamine, serglycin proteoglycans, and several MC-specific proteases: chymases, tryptases, and carboxypeptidase A. Although the exact effector mechanism(s) by which MCs carry out their either beneficial or harmful effects in vivo are in large parts unknown, it is reasonable to assume that these mediators may contribute in profound ways. Among the various MC mediators, the exact biological function of the MC proteases has for a long time been relatively obscure. However, recent progress involving successful genetic targeting of several MC protease genes has generated powerful tools, which will enable us to unravel the role of the MC proteases both in normal physiology as well as in pathological settings. This chapter summarizes the current knowledge of the biology of the MC proteases.