In vivo evoked specific cell mediated cytotoxicity in carp (Cyprinus carpio L.) uses mainly a perforin/granzyme-like pathway

Transcription factor networks drive perforin activity in the anti-bacterial immune response of tilapia

Perforin, produced by natural killer (NK) cells and cytotoxic T lymphocytes (CTLs), is one of the effectors of cell-mediated cytotoxicity (CMC) in vertebrates, playing a paramount role in killing target cells. However, whether and how perforin is involved in adaptive immune responses in early vertebrates remains unclear. Using Nile tilapia (Oreochromis niloticus) as a model, we investigated the characteristics of perforin in early vertebrates. Oreochromis niloticus perforin (OnPRF) possesses 2 conserved functional domains, membrane attack complex/perforin (MACPF) and protein kinase C conserved region 2 (C2) domains, although they share low amino acid sequence similarity with other homologs. OnPRF was widely expressed in various immune tissues and could respond to lymphocyte activation and T-cell activation in vitro at both the transcriptional and protein levels, indicating that it may be involved in adaptive immune responses. Furthermore, after infection with Edwardsiella piscicida and Aeromonas hydrophila, the mRNA and protein levels of OnPRF were significantly up-regulated within the adaptive immune response period. Additionally, we revealed that many transcription factors were involved in the transcriptional regulation of OnPRF, including p65, c-Fos, c-Jun, STAT1 and STAT4, and there was a synergy among these transcription factors. Overall, these findings demonstrate the involvement of OnPRF in T-cell activation and adaptive immune response in tilapia, thus providing new evidence for comprehending the evolution of immune response in early vertebrates.

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.

Carp edema virus and immune response in carp (Cyprinus carpio): Current knowledge

The importance of world aquaculture production grows annually together with the increasing need to feed the global human population. Common carp (Cyprinus carpio) is one of the most important freshwater fish in global aquaculture. Unfortunately, carp production is affected by numerous diseases of which viral diseases are the most serious. Koi herpesvirus disease (KHVD), spring viraemia of carp (SVC), and during the last decades also koi sleepy disease (KSD) are currently the most harmful viral diseases of common carp. This review summarizes current knowledge about carp edema virus (CEV), aetiological agent causing KSD, and about the disease itself. Furthermore, the article is focused on summarizing the available information about the antiviral immune response of common carp, like production of class I interferons (IFNs), activation of cytotoxic cells, and production of antibodies by B cells focusing on anti-CEV immunity.

Effect of growth rate on transcriptomic responses to immune stimulation in wild-type, domesticated, and GH-transgenic coho salmon

BACKGROUND

Transcriptomic responses to immune stimulation were investigated in coho salmon (Oncorhynchus kisutch) with distinct growth phenotypes. Wild-type fish were contrasted to strains with accelerated growth arising either from selective breeding (i.e. domestication) or genetic modification. Such distinct routes to accelerated growth may have unique implications for relationships and/or trade-offs between growth and immune function.

RESULTS

RNA-Seq was performed on liver and head kidney in four 'growth response groups' injected with polyinosinic-polycytidylic acid (Poly I:C; viral mimic), peptidoglycan (PGN; bacterial mimic) or PBS (control). These groups were: 1) 'W': wild-type, 2) 'TF': growth hormone (GH) transgenic salmon with ~ 3-fold higher growth-rate than W, 3) 'TR': GH transgenic fish ration restricted to possess a growth-rate equal to W, and 4) 'D': domesticated non-transgenic fish showing growth-rate intermediate to W and TF. D and TF showed a higher similarity in transcriptomic response compared to W and TR. Several immune genes showed constitutive expression differences among growth response groups, including perforin 1 and C-C motif chemokine 19-like. Among the affected immune pathways, most were up-regulated by Poly I:C and PGN. In response to PGN, the c-type lectin receptor signalling pathway responded uniquely in TF and TR. In response to stimulation with both immune mimics, TR responded more strongly than other groups. Further, group-specific pathway responses to PGN stimulation included NOD-like receptor signalling in W and platelet activation in TR. TF consistently showed the most attenuated immune response relative to W, and more DEGs were apparent in TR than TF and D relative to W, suggesting that a non-satiating ration coupled with elevated circulating GH levels may cause TR to possess enhanced immune capabilities. Alternatively, TF and D salmon are prevented from acquiring the same level of immune response as TR due to direction of energy to high overall somatic growth. Further study of the effects of ration restriction in growth-modified fishes is warranted.

CONCLUSIONS

These findings improve our understanding of the pleiotropic effects of growth modification on the immunological responses of fish, revealing unique immune pathway responses depending on the mechanism of growth acceleration and nutritional availability.

Molecular characterization of three novel perforins in common carp (Cyprinus carpio L.) and their expression patterns during larvae ontogeny and in response to immune challenges

Background

In the host immune system, perforin is a cytotoxic effector molecule that eliminate virus-infected and malignant cells. Moreover, some recent studies also imply the involvement of perforin in antibacterial immunity. Common carp (Cyprinus carpio L.), one of the most economically important fish species in China, has a high susceptibility to viruses and bacteria. Thus far, in common carp, no data are available regarding the identification and immunologic function of the perforin.

Results

In the present study, the cDNA and genomic DNA sequences of three perforin isoform genes were cloned and characterized in common carp, named CcPRF1, CcPRF2 and CcPRF3. Amino acid sequences of the three CcPRFs were quite different, with identities ranged from 37.3 to 39.5%. Phylogenetic analysis showed that three CcPRFs, each in a separate sub-branch, possessed closer evolutionary relationship with other teleost perforins, especially with cyprinid fishes, than higher vertebrates. Expression analysis revealed that each CcPRF gene was differentially expressed in all of the nine tested tissues. During larvae ontogeny, each CcPRF displayed a distinct expression pattern, while with a common expression peak at 22 days post hatching (dph). Moreover, in vivo or in vitro, after stimulation with polyI:C, LPS and Aeromonas hydrophila, each CcPRF was induced significantly, with differential expression dynamics.

Conclusions

Our findings suggest that perforin might play significant roles in larval immune system and in the immune defense of common carp against viral and bacterial pathogens. Meantime, the differential expression dynamics seem to imply possible different cellular locations or functional differences across various CcPRF isoforms.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1613-y) contains supplementary material, which is available to authorized users.

T Cells in Fish

Cartilaginous and bony fish are the most primitive vertebrates with a thymus, and possess T cells equivalent to those in mammals. There are a number of studies in fish demonstrating that the thymus is the essential organ for development of T lymphocytes from early thymocyte progenitors to functionally competent T cells. A high number of T cells in the intestine and gills has been reported in several fish species. Involvement of CD4⁺ and CD8α⁺ T cells in allograft rejection and graft-versus-host reaction (GVHR) has been demonstrated using monoclonal antibodies. Conservation of CD4⁺ helper T cell functions among teleost fishes has been suggested in a number studies employing mixed leukocyte culture (MLC) and hapten/carrier effect. Alloantigen- and virus-specific cytotoxicity has also been demonstrated in ginbuna and rainbow trout. Furthermore, the important role of cell-mediated immunity rather than humoral immunity has been reported in the protection against intracellular bacterial infection. Recently, the direct antibacterial activity of CD8α⁺, CD4⁺ T-cells and sIgM⁺ cells in fish has been reported. In this review, we summarize the recent progress in T cell research focusing on the tissue distribution and function of fish T cells.

Identification of a novel fish granzyme involved in cell-mediated immunity

Granzymes (Gzms) are serine proteases released from cytoplasmic granules within cytotoxic T lymphocytes and natural killer (NK) cells. Gzms induce apoptosis within virus-infected and transformed cells. In fish as well as mammals, Gzms appear to play a major role in inducing target cell death. However, information on the function of fish Gzms is limited, although Gzm-like genes have been reported in several species. We identified and characterized a fish Gzm (termed gcGzm) in ginbuna crucian carp, Carassius auratus langsdorfii. The primary structure of gcGzm resembled mammalian GzmB, and gcGzm clustered with mammalian GzmB by phylogenetic tree analysis. gcGzm was secreted from HEK293T cells transfected with gcgzm cDNA and was predominantly expressed in CD8(+) T cells, as in mammals. Expression of gcgzm mRNA was greatly enhanced by allo-sensitization and infection with the intracellular pathogen Edwardsiella tarda, indicating that gcGzm is involved in cell-mediated immunity. However, its enzymatic activity was different from mammalian Gzms because gcGzm did not cleave the known substrates for mammalian Gzms. Thus we conclude that the newly discovered gcGzm is a novel secretory serine protease involved in cell-mediated immunity in fish, with similar structure to human GzmB but different substrate specificity.

Cytotoxic T cells in teleost fish

The presence of antigen-specific cytotoxic T cells has been suggested in a number of in vivo and in vitro studies in fish. Acute allograft rejection with an accelerated response on second-set grafts and the presence of graft-versus-host reaction (GVHR) has been reported in teleost. Alloantigen- and virus-specific cytotoxicity has also been demonstrated in ex vivo studies in ginbuna and rainbow trout. In addition, alloantigen-specific cytotoxic T cell clones have been produced in cultures initiated with peripheral blood leukocytes (PBL) from an alloantigen-immunized channel catfish. Over the last decade several fish genomes have been sequenced and genetic information is rapidly accumulating. Thanks to these genome data bases and EST analysis, mRNA expression of T cell surface marker genes in alloantigen- or virus-specific effector cells has been reported in some fish species, e.g. TCR α or β and CD8α in ginbuna and rainbow trout, and TCR α, β or γ in channel catfish. These findings suggest the presence of CD8(+) cytotoxic T lymphocyte (CTL) in fish similar to those of higher vertebrates. Recently, monoclonal antibodies against CD8α and CD4 antigens have been produced in some fish species. Investigation on the characteristics of CTL and cell-mediated immune mechanisms is now possible at defined T cell subsets, although identification of T cell subset is limited in a few fish species at present. In this review, we describe the recent progress in this field focusing on cells involved in antigen specific cytotoxicity.

Granule-derived granzyme B mediates the vulnerability of human neurons to T cell-induced neurotoxicity

Multiple sclerosis (MS) is considered an autoimmune disease of the CNS and is characterized by inflammatory cells infiltrating the CNS and inducing demyelination, axonal loss, and neuronal death. Recent evidence strongly suggests that axonal and neuronal degeneration underlie the progression of permanent disability in MS. In this study, we report that human neurons are selectively susceptible to the serine-protease granzyme B (GrB) isolated from cytotoxic T cell granules. In vitro, purified human GrB induced neuronal death to the same extent as the whole activated T cell population. On the contrary, activated T cells isolated from GrB knockout mice failed to induce neuronal injury. We found that following internalization through various parts of neurons, GrB accumulated in the neuronal soma. Within the cell body, GrB diffused out of endosomes possibly through a perforin-independent mechanism and induced subsequent activation of caspases and cleavage of α-tubulin. Inhibition of caspase-3, a well-known substrate for GrB, significantly reduced GrB-mediated neurotoxicity. We demonstrated that treatment of neurons with mannose-6-phosphate prevented GrB entry and inhibited GrB-mediated neuronal death, suggesting mannose-6-phosphate receptor-dependent endocytosis. Together, our data unveil a novel mechanism by which GrB induces selective neuronal injury and suggest potential new targets for the treatment of inflammatory-mediated neurodegeneration in diseases such as MS.

Viral hemorrhagic septicaemia virus (VHSV) up-regulates the cytotoxic activity and the perforin/granzyme pathway in the rainbow trout RTS11 cell line

A survey of immune-relevant genes that might be up-regulated in response to viral hemorrhagic septicaemia virus (VHSV) in the rainbow trout monocyte-macrophage cell line, RTS11, unexpectedly revealed an increased expression of perforin (PRF) and granzyme (GRZ) genes, which represent components of the major cytotoxic pathway. The natural killer-enhancing factor (NKEF), also known to modulate cytotoxic activity, was up-regulated at the gene but strikingly down-regulated at protein level. The expression of these genes was not affected in head kidney leukocytes (HKLs) infected with VHSV, leading us to evaluate the potential cytotoxic activity of RTS11 and HKLs. For the first time, the cytotoxic activity of RTS11 against xenogeneic targets has been demonstrated, although this was modest relative to HKLs. Yet the activity in RTS11 was significantly increased by VHSV, as in HKLs. This cytotoxic activity elicited by viral infection appeared to require viral gene expression because inactivated VHSV failed to increase RTS11 cytotoxic activity. As for other immune functions, RTS11 cells provide a model for further studying cytotoxic activities of fish monocyte-macrophages.

Perforin-dependent cytotoxic mechanism in killing by CD8 positive T cells in ginbuna crucian carp, Carassius auratus langsdorfii

T cell-mediated cytotoxicity occurs via pathways based on perforin or Fas mechanisms. Perforin is a protein present in the cytoplasmic granules of CD8(+) cytotoxic T lymphocytes and is secreted to form pores on target cell membranes. In fish, although the involvement of perforin in cytotoxicity have been suggested for several species, perforin-mediated cytotoxicity of CD8α(+) lymphocyte in conjunction with expression of the perforin gene has not been reported. In order to investigate the killing mechanism of CD8α(+) lymphocytes by perforin-mediated pathway in fish, we measured apoptosis of target cells triggered by CD8α(+) lymphocytes, performed cytotoxic assays in the presence or absence of perforin inhibitor; concanamycin A and EGTA, and analysed the expression of perforin1, perforin2 and perforin3 isotypic genes in ginbuna crucian carp. In the present study, we found that CTLs attached with target cells. CTL should have direct contact with target cells to kill them. Approximately 50% of target cells were positive for annexin V after co-cultured with CD8α(+) lymphocytes, indicating the induction of apoptotic cell death. Concanamycin A, which induces depolymerization of perforin resulting in lytic function, suppressed the cytotoxicity of CD8α(+) cells in a dose-dependent manner. In addition, cytotoxicity mediated by CD8α(+) lymphocytes were significantly suppressed by the addition of the Ca(2+)-chelating agents EGTA or EGTA-Mg(2+), and the addition of Ca(2+) restored the killing mechanism of target cells. We further found enhanced expression of perforin1 but not perforin2 or perforin3 in CTLs from allo-sensitized fish. The present study has demonstrated that ginbuna CTLs kill target cells through perforin-mediated pathway, suggesting that perforin-mediated pathway is conserved throughout vertebrate.

Immune-related, lectin-like receptors are differentially expressed in the myeloid and lymphoid lineages of zebrafish

The identification of C-type lectin (Group V) natural killer (NK) cell receptors in bony fish has remained elusive. Analyses of the Fugu rubripes genome database failed to identify Group V C-type lectin domains (Zelensky and Gready, BMC Genomics 5:51, 2004) suggesting that bony fish, in general, may lack such receptors. Numerous Group II C-type lectin receptors, which are structurally similar to Group V (NK) receptors, have been characterized in bony fish. By searching the zebrafish genome database we have identified a multi-gene family of Group II immune-related, lectin-like receptors (illrs) whose members possess inhibiting and/or activating signaling motifs typical of Group V NK receptors. Illr genes are differentially expressed in the myeloid and lymphoid lineages, suggesting that they may play important roles in the immune functions of multiple hematopoietic cell lineages.