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

Non-specific cytotoxic cell receptor protein-1 (NCCRP-1) is involved in anti-parasite innate CD8+ T cell-mediated cytotoxicity in ginbuna crucian carp

CD8⁺ cytotoxic T cells (CTLs) are a main cellular component of adaptive immunity. Our previous research has shown that CD8⁺ cells demonstrate spontaneous cytotoxic activity against the parasite Ichthyophthirius multifiliis in ginbuna crucian carp, suggesting that CD8⁺ cells play an important role in innate immunity. Herein, we investigated the molecules and cellular signal pathways involved in the cytotoxic response of ginbuna crucian carp. We considered non-specific cytotoxic receptor protein-1 (NCCRP-1) as candidate molecule for parasite recognition. We detected NCCRP-1 protein in CD8⁺ cells and the thymus as well as in other cells and tissues. CD8⁺ cells expressed mRNA for NCCRP-1, Jak2, and T cell-related molecules. In addition, treatment with a peptide containing the presumed antigen recognition site of ginbuna NCCRP-1 significantly inhibited the cytotoxic activity of CD8⁺ cells against the parasites. The cytotoxic activity of CD8⁺ cells was significantly inhibited by treatment with the JAK1/2 inhibitor baricitinib. These results suggest that teleost CTLs recognize I. multifiliis through NCCRP-1 and are activated by JAK/STAT signaling.

Regulation of Il-2 on the expression of granzyme B- and perforin-like genes and its functional implication in grass carp peripheral blood neutrophils

Granzyme (Gzm) B and perforin, both as cytotoxic proteins, can collaborate to induce the death of target cells as well as the microbes. They were originally discovered in cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells and confer the cytotoxic activities of these cells. In the present study, the coding sequences of a granzyme b-like (gcgzmbl) and a perforin-like (gcprfl) genes were cloned from grass carp (Ctenopharyngodon idellus) and their specific antibodies were subsequently prepared and validated. The mRNA and protein expression of these two cytotoxic proteins in grass carp peripheral blood neutrophils was demonstrated by quantitative PCR (qPCR) and immunofluorescence staining, respectively. In the same cell model, expression of gcGzmbl and gcPrfl was stimulated by grass carp interleukin (Il)-2 in a dose- and time-dependent manners and Erk, NF-κB and Stat5 pathways were found to be involved in the regulation of Il-2 on the genes' expression. Additionally, glycolysis was proved to play a role in the stimulation of Il-2 on gcGzmbl and gcPrfl expression in peripheral blood neutrophils. As combating the invading microorganisms is one of the main functions of neutrophils, the roles of gcGzmbl and gcPrfl in the anti-bacterial activities of grass carp peripheral blood neutrophils were explored. Results showed that immunoneutralization of gcGzmbl or gcPrfl significantly attenuated the antimicrobial abilities of the neutrophils enhanced by Il-2. These findings shed a light on the expression, regulation and functions of granzyme B- and perforin-like proteins in fish peripheral blood neutrophils and enrich the understanding of Il-2 function in fish innate immunity.

Immunological memory in teleost fish

Immunological memory can be regarded as the key aspect of adaptive immunity, i.e. a specific response to first contact with an antigen, which in mammals is determined by the properties of T, B and NK cells. Re-exposure to the same antigen results in a more rapid response of the activated specific cells, which have a unique property that is the immunological memory acquired upon first contact with the antigen. Such a state of immune activity is also to be understood as related to "altered behavior of the immune system" due to genetic alterations, presumably maintained independently of the antigen. It also indicates a possible alternative mechanism of maintaining the immune state at a low level of the immune response, "directed" by an antigen or dependent on an antigen, associated with repeated exposure to the same antigen from time to time, as well as the concept of innate immune memory, associated with epigenetic reprogramming of myeloid cells, i.e. macrophages and NK cells. Studies on Teleostei have provided evidence for the presence of immunological memory determined by T and B cells and a secondary response stronger than the primary response. Research has also demonstrated that in these animals macrophages and NK-like cells (similar to mammalian NK cells) are able to respond when re-exposed to the same antigen. Regardless of previous reports on immunological memory in teleost fish, many reactions and mechanisms related to this ability require further investigation. The very nature of immunological memory and the activity of cells involved in this process, in particular macrophages and NK-like cells, need to be explained. This paper presents problems associated with adaptive and innate immune memory in teleost fish and characteristics of cells associated with this ability.

Tipping the Scales With Zebrafish to Understand Adaptive Tumor Immunity

The future of improved immunotherapy against cancer depends on an in-depth understanding of the dynamic interactions between the immune system and tumors. Over the past two decades, the zebrafish has served as a valuable model system to provide fresh insights into both the development of the immune system and the etiologies of many different cancers. This well-established foundation of knowledge combined with the imaging and genetic capacities of the zebrafish provides a new frontier in cancer immunology research. In this review, we provide an overview of the development of the zebrafish immune system along with a side-by-side comparison of its human counterpart. We then introduce components of the adaptive immune system with a focus on their roles in the tumor microenvironment (TME) of teleosts. In addition, we summarize zebrafish models developed for the study of cancer and adaptive immunity along with other available tools and technology afforded by this experimental system. Finally, we discuss some recent research conducted using the zebrafish to investigate adaptive immune cell-tumor interactions. Without a doubt, the zebrafish will arise as one of the driving forces to help expand the knowledge of tumor immunity and facilitate the development of improved anti-cancer immunotherapy in the foreseeable future.

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.

Innate cell-mediated cytotoxicity of CD8+ T cells against the protozoan parasite Ichthyophthirius multifiliis in the ginbuna crucian carp, Carassius auratus langsdorfii

Cytotoxic T cells are known to have the ability to kill microbe-infected host cells, which makes them essential in the adaptive immunity processes of various vertebrates. In this study, we demonstrated innate cell-mediated cytotoxicity of CD8⁺ T cells against protozoan parasites found in the ginbuna crucian carp. When isolated effector cells such as CD8⁺, CD4⁺ (CD4-1⁺), or CD8^- CD4^- (double-negative, DN), from naïve ginbuna crucian carp were co-incubated with target parasites (Ichthyophthirius multifiliis), CD8⁺ cells from the kidney and gill showed the highest cytotoxic activity. On the other hand, DN cells, which include macrophages and CD4^- CD8^- lymphocytes, showed the lowest cytotoxic activity against I. multifiliis. Additionally, the cytotoxic activity of CD8⁺ cells was found to significantly decrease in the presence of a membrane separating the effector cells from I. multifiliis. Furthermore, the serine protease inhibitor 3,4-dichloroisocoumarin and perforin inhibitor concanamycin A significantly inhibited the cytotoxic activity of CD8⁺ cells. These results demonstrate that CD8⁺ T cells of ginbuna crucian carp can kill extracellular parasites in a contact-dependent manner via serine proteases and perforin. Therefore, we conclude that CD8⁺ T cells play an essential role in anti-parasite innate immunity of teleost fish.

Characterisation of IL-15 and IL-2Rβ in grass carp: IL-15 upregulates cytokines and transcription factors of type 1 immune response and NK cell activation

Interleukin (IL) -15 belongs to the common cytokine receptor γ chain (γC) family and has diverse functions in regulating the development, proliferation and activation of NK and T cells. It activates a hetero-trimeric receptor complex consisting of IL-2Rα, IL-2Rβ and a common γ chain (γC). In this study, the full-length cDNA sequences of IL-15 and IL-2Rβ were identified in grass carp (Ctenopharyngodon idella, Ci) and their expression profiles analysed. The CiIL-15 and CiIL-2Rβ were shown to be broadly expressed in tissues, with the highest levels detected in the spleen. Moreover, the CiIL-15 and CiIL-2Rβ were modulated in primary head kidney leucocytes (HKLs) and splenocytes by immunostimulants and cytokines, and in the head kidney and spleen of fish after infection of Flavobacterium columnare and grass carp reovirus. The bioactivity of bacteria derived recombinant CiIL-15 protein was evaluated in the primary leucocytes. The CiIL-15 was shown to induce signature genes of type 1 immune response (IFN-γ and T-bet) and NK cell activation (perforin and Eomesa), whilst exhibiting inhibitory effects on the genes involved in the type 2 immune response (IL-4/13, IL-10 and Gata3). Our data suggest that IL-15 is a key regulator in promoting the type 1 immune response and NK cell activation in fish.

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.

A Comparison of the Innate and Adaptive Immune Systems in Cartilaginous Fish, Ray-Finned Fish, and Lobe-Finned Fish

The immune system is composed of two subsystems-the innate immune system and the adaptive immune system. The innate immune system is the first to respond to pathogens and does not retain memory of previous responses. Innate immune responses are evolutionarily older than adaptive responses and elements of innate immunity can be found in all multicellular organisms. If a pathogen persists, the adaptive immune system will engage the pathogen with specificity and memory. Several components of the adaptive system including immunoglobulins (Igs), T cell receptors (TCR), and major histocompatibility complex (MHC), are assumed to have arisen in the first jawed vertebrates-the Gnathostomata. This review will discuss and compare components of both the innate and adaptive immune systems in Gnathostomes, particularly in Chondrichthyes (cartilaginous fish) and in Osteichthyes [bony fish: the Actinopterygii (ray-finned fish) and the Sarcopterygii (lobe-finned fish)]. While many elements of both the innate and adaptive immune systems are conserved within these species and with higher level vertebrates, some elements have marked differences. Components of the innate immune system covered here include physical barriers, such as the skin and gastrointestinal tract, cellular components, such as pattern recognition receptors and immune cells including macrophages and neutrophils, and humoral components, such as the complement system. Components of the adaptive system covered include the fundamental cells and molecules of adaptive immunity: B lymphocytes (B cells), T lymphocytes (T cells), immunoglobulins (Igs), and major histocompatibility complex (MHC). Comparative studies in fish such as those discussed here are essential for developing a comprehensive understanding of the evolution of the immune system.

Intracellular Bacterial Infections: A Challenge for Developing Cellular Mediated Immunity Vaccines for Farmed Fish

Aquaculture is one of the most rapidly expanding farming systems in the world. Its rapid expansion has brought with it several pathogens infecting different fish species. As a result, there has been a corresponding expansion in vaccine development to cope with the increasing number of infectious diseases in aquaculture. The success of vaccine development for bacterial diseases in aquaculture is largely attributed to empirical vaccine designs based on inactivation of whole cell (WCI) bacteria vaccines. However, an upcoming challenge in vaccine design is the increase of intracellular bacterial pathogens that are not responsive to WCI vaccines. Intracellular bacterial vaccines evoke cellular mediated immune (CMI) responses that “kill” and eliminate infected cells, unlike WCI vaccines that induce humoral immune responses whose protective mechanism is neutralization of extracellular replicating pathogens by antibodies. In this synopsis, I provide an overview of the intracellular bacterial pathogens infecting different fish species in aquaculture, outlining their mechanisms of invasion, replication, and survival intracellularly based on existing data. I also bring into perspective the current state of CMI understanding in fish together with its potential application in vaccine development. Further, I highlight the immunological pitfalls that have derailed our ability to produce protective vaccines against intracellular pathogens for finfish. Overall, the synopsis put forth herein advocates for a shift in vaccine design to include CMI-based vaccines against intracellular pathogens currently adversely affecting the aquaculture industry.

Effects of IFNγ administration on allograft rejection in ginbuna crucian carp

In vertebrates, the rejection of allografts is primarily accomplished by cell-mediated immunity. We recently identified four IFNγ isoforms with antiviral activity in ginbuna crucian carp, Carassius auratus langsdorfii. However, involvement of the IFNγ isoforms in cell-mediated immunity, especially in T cell function remains unknown. Here we investigate expression of the IFNγ isoforms and effects of administration of recombinant IFNγ (rgIFNγ) isoforms in ginbuna scale allograft rejection. All four IFNγ isoforms showed significantly higher expression with the progression of graft rejection. Administration of rgIFNγrel 1 but not rgIFNγrel 2, rgIFNγ1 nor rgIFNγ2 enhanced allograft rejection. The number of CD4(+) and CD8α(+) cells increased in early stages of rejection, while sIgM(+) cells were higher than controls at day 0 and 5 in the rgIFNγrel 1 administrated group. Expression of IFNγ1 and IFNγ2 mRNA was significantly up-regulated by rgIFNγrel 1 administration, while that of IFNγrel 1 and IFNγrel 2 was not. These results suggest different contributions of the four IFNγ isoforms toward the immune responses comprising allograft rejection.

Purification and characterization of a fish granzymeA involved in cell-mediated immunity

Granzymes are serine proteases involved in the induction of cell death against non-self cells. The enzymes differ in their primary substrate specificity and have one of four hydrolysis activities: tryptase, Asp-ase, Met-ase and chymase. Although granzyme genes have been isolated from several fishes, evidence for their involvement in cytotoxicity has not yet been reported. In the present study, we attempted to purify and characterize a fish granzyme involved in cytotoxicity using ginbuna crucian carp. The cytotoxicity of leukocytes was significantly inhibited by the serine protease inhibitor ''3, 4-dichloroisocoumarin''. In addition, we found that granzymeA-like activity (hydrolysis of Z-GPR-MCA) was inhibited by the same inhibitor and significantly enhanced by allo-antigen stimulation in vivo. Proteins from leukocyte extracts were subjected to two steps of chromatographic purification using benzamidine-Sepharose and SP-Sepharose. The molecular weight of the purified enzyme was estimated to be 26,900 Da by SDS-PAGE analysis. The purified enzyme displayed a Km of 220 μM, a Kcat of 21.7 sec(-1) and a Kcat/Km of 98,796 sec(-1) M(-1) with an optimal pH of 9.5 for the Z-GPR-MCA substrate. The protease was totally inhibited by serine protease inhibitors and showed granzymeA-like substrate specificity. Therefore, we conclude that the purified enzyme belongs to the mammalian granzymeA (EC 3.4.21.78) and appears to be involved in cytotoxicity in fish.

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.

Kinetics of lymphocyte subpopulations in allogeneic grafted scales of ginbuna crucian carp

In mammals the rejection of allografts is primarily accomplished by cell-mediated immunity including T cells. Recently, considerable studies reveal the existence of helper and cytotoxic T cell subsets in fish. Here we investigate the kinetics of CD4(+) and CD8α(+) T cells along with sIgM(+) cells and phagocytic cells in an allogeneic scale graft model using ginbuna crucian carp for understanding the mechanisms of cell-mediated immune response. The results showed that CD4(+) T cells first infiltrated into allogeneic scales followed by CD8α(+) and sIgM(+) cells, and finally phagocytic cells appeared in the graft. Furthermore, most of the CD8α(+) T cells appeared on the border of the allografted scales at the time of rejection. These results suggest that T cells play crucial roles and work together with other cell types for completion of allograft rejection.