Cloning and regulation of the major histocompatibility class I alpha gene in the teleost fish gilthead seabream

Cloning, Exogenous Expression and Function Analysis of Interferon–γ from Gadus macrocephalus

Interferon γ (IFN–γ) is now considered to be one of the key molecules in the regulation of innate and adaptive immunity. The function of IFN–γ is best described in humans, but less of IFN–γ in fish species has been described at protein level. In the present study, IFN–γ from Gadus macrocephalus (GmIFN–γ) has been examined in terms of bioinformatics, prokaryotic expression, yeast expression, antiviral activity and immune regulatory function. The cDNA of GmIFN–γ contains an open reading frame of 570 nucleotides, coding 189 amino acids. The mature protein contains a nuclear localization signal motif and an obvious IFN–γ signature sequence at the C-terminal. GmIFN–γ is very similar to that of Atlantic cod, with homology up to 89.89%, but less than 32% to other species. GmIFN–γ can be detected in the gills, spleen, intestine, brain and kidney. Interestingly, during early development, a strong signal of GmIFN–γ was not detected until 40 days post hatching. Prokaryotic expression plasmid pET–32a–GmIFN–γ was constructed, and the expression products in BL21 were confirmed by Mass Spectrometry. Meanwhile, the plasmid pGAPZA–GmIFN–γ with Myc tag was constructed and transmitted into Pichia pastoris yeast GS115, and the products were tested using Western blot. The purified GmIFN–γ from either BL21 or yeast has a strong antivirus (Spring viremia of carp virus) effect. The vector of pcDNA3.1–GmIFN–γ was expressed in EPC cell lines; high transcript levels of MHC class I chain-related protein A (MICA) gene were detected; and the exogenous GmIFN–γ protein could also induce MICA expression, indicating that GmIFN–γ could stimulate immune response. The yeast GS115 with GmIFN–γ protein, which is an inclusion body, was given to zebrafish orally, and the transcript of zebrafish IFN–γ was upregulated significantly; however, genes of the interferon type–I signal pathway were not well stimulated.

Expression of immune genes in Indian major carp, Catla catla challenged with Flavobacterium columnare

Columnaris disease, caused by Flavobacterium columnare, is one of the important bacterial diseases responsible for large-scale mortalities in numerous freshwater fishes globally. This disease can cause up to 100% mortality within 24 h of infection and is considered to be a cause of concern for aquaculture industry. Despite being a serious disease, scarce information is available regarding host-pathogen interaction, particularly the modulation of different immune genes in response to F. columnare infection. Therefore, in the present study, an attempt has been made to study expression of important immune regulatory genes, namely IL-1β, iNOS, INF-γ, IL-10, TGF-β, C3, MHC-I and MHC-II in gills and kidney of Catla catla following experimental infection with F. columnare. The expression analysis of immune genes revealed that transcript levels of IL-1β, iNOS, IL-10, TGF-β, C3 and MHC-I were significantly up-regulated (p < 0.05) in both the organs of the infected catla. IFN-γ and MHC-II were up-regulated in gills of infected catla whereas, both the genes showed down-regulation in kidney. The results indicate that important immune genes of C. catla are modulated following infection with F. columnare. The knowledge thus generated will strengthen the understanding of molecular pathogenesis of F. columnare in Indian major carp C. catla.

Effects of dietary glucose and starch levels on the growth, apparent digestibility, and skin-associated mucosal non-specific immune parameters in juvenile blunt snout bream (Megalobrama amblycephala)

A 10-week feeding trial was performed to evaluate the effects of different types and levels of carbohydrates in growth performance, apparent digestibility coefficients and skin-associated mucosal non-specific immune parameters in blunt snout bream (Megalobrama amblycephala). Fish were randomly fed four diets containing two carbohydrates (glucose and starch) diets and two carbohydrates levels (330 and 440 g kg^-1). High carbohydrate levels remarkably increased the weight gain rate (WGR), apparent digestibility of dry matters, protein and carbohydrates, body crud protein content, plasma levels of aspartate transaminase (AST), and skin-associated mucosal levels of immunoglobulin M (IgM), HDL cholesterol, lysozyme (LZM), advanced the transcriptions of mucin 2 (Muc2), mucin 5b (Muc5b) and apolipoprotein A-I (apoA-I), whereas the opposite was true for feed conversion ratio (FCR), plasma levels of IgM, skin-associated mucosal levels of major histocompatibility complex (MHC) and β-Defensins, and the transcriptions of heat shock protein 60 (Hsp60). In addition, carbohydrate types of glucose remarkably increased the survival rate, apparent digestibility of dry matters, protein and carbohydartes, body crud ash, plasma levels of total protein (TP), globulin (GLB), immunoglobulin M (IgM), complement C3 and complement C4 and the transcriptions of Muc5b. Whereas the carbohydrate types of starch remarkably increased viscerosomatic index (VSI), hepatosomatic index (HSI), condition factor (CF), abdominal fat percentage (AFP), apparent digestibility of liquid, advanced the transcriptions of Muc2, apoA-I and heat shock protein 70 (Hsp70). Significant interactions between different types and levels of dietary carbohydrates were also observed in WGR, apparent digestibility of dry matters, protein and liquid, body crud ash, plasma levels of TP, albumin (ALB) and AST, skin-associated mucosal levels of major histocompatibility complex (MHC) and β-Defensins, and the transcriptions of Muc2 and Muc5b. Our results indicate that inclusion of high level of glucose in the diet of blunt snout bream could improve growth performance, nonspecific immunity, and increase the efficiency of protein, which is suggesting that high level of glucose could be used in feed production. However, the proportion of the specific formula of glucose using in feed needs further study.

Ontogenetic onset of immune-relevant genes in the common sole (Solea solea)

Fish are free-living organisms since initial stages of development and are exposed to numerous pathogens before their lymphoid organs have matured and adaptive immunity has developed. Susceptibility to diseases and juvenile mortality represent key critical factors for aquaculture. In this context, the characterization of the appearance kinetics of the immune system key members will be useful in understanding the ability of a particular species in generating immune protection against invading pathogens at different developmental stages. The present study characterized, for the first time, the transcriptional onset of un-explored relevant genes of both innate and adaptive immune system during the Solea solea ontogenesis. Gene expression profiles of immune relevant genes was investigated, by means of DNA microarray, in ten developmental stages, from hatching (1 day post-hatching, dph) to accomplishment of the juvenile form (33 dph). The obtained results revealed that transcripts encoding relevant members of innate immune repertoire, such as lysozyme, AMPs (hepcidin, β-defensin), PPRs and complement components are generally characterized by high expression levels at first stages (i.e. hatch and first feeding) indicating protection from environmental pathogens even at early development. Transcription of adaptive immune genes (i.e. Class I and class II MHC, TCRs) differs from that of the innate immune system. Their onset coincides with metamorphosis and larvae-to-juvenile transition, and likely overlaps with the appearance and maturation of the main lymphoid organs. Finally, data collected suggest that at the end of metamorphosis S. solea cell-mediated immune system hasn't still undergone full maturation.

Genomic sequences comparison and differential expression of miiuy croaker MHC class I gene, after infection by Vibrio anguillarum

Major histocompatibility complex (MHC) has a central role in the adaptive immune system by presenting foreign peptide to the T-cell receptor. MHC gene family contains two main subgroups of immunologically active molecules. In order to study the molecular function and genomic characteristic of class I gene in teleost, the full lengths of MHC class Iα cDNA and genomic sequence were cloned from miiuy croaker (Miichthys miiuy). Seven exons and six introns were identified in miiuy croaker class Iα gene. This genomic structural feature of miiuy croaker is similar to that present in some fishes such as Japanese flounder and Atlantic salmon, but different from that present in some other fishes such as half-smooth tongue sole and channel catfish. The deduced amino acid sequence of class Iα gene had 25.9-54.1% identity with those of mammal and teleost. Real-time quantitative RT-PCR demonstrated that the MHC class Iα gene was ubiquitously expressed in 10 normal tissues; expression levels of MHC Iα gene were found first upregulated and then downregulated throughout the pathogenic bacteria infection process in spleen and kidney.

Molecular modelling of co-receptor CD8 alpha alpha and its complex with MHC class I and T-cell receptor in sea bream (Sparus aurata)

T-cells are the main actors of cell-mediated immune defence; they recognize and respond to peptide antigens associated with MHC class I and class II molecules. In this paper, we investigated by molecular modelling methods in the teleost sea bream (Sparus aurata) the interaction among the molecules of the tertiary complex CD8/MHC-I/TCR, which determines the T-cell-mediated immunological response to foreign molecules. First, we predicted the three-dimensional structure of CD8 alpha alpha dimer and MHC-I, and, successively, we simulated the CD8 alpha alpha/MHC-I complex. Finally, the 3D structure of the CD8/MHC-I/TCR complex was simulated in order to investigate the possible changes that can influence TCR signalling events.

In vivo actions of melatonin on the innate immune parameters in the teleost fish gilthead seabream

Melatonin, a molecule produced in the pineal gland and retina of vertebrates, plays a major role in day-night circadian rhythms and other physiological processes, including the immune responses. Because little is known in this respect in fish, we have evaluated the in vivo role of melatonin in the main innate immune activities and the expression of immune-relevant genes in a teleost fish, the gilthead seabream (Sparus aurata L.). An intraperitoneal injection of 1 or 10 mg melatonin/kg of body weight produced a dose-time dependent increase in circulating melatonin serum levels. Several innate immune responses such as peroxidase, phagocytic, reactive oxygen intermediates and cell-mediated cytotoxic activities were significantly enhanced by the administration of melatonin at different sampling times. The expression of immune-relevant genes such as interleukin-1beta, major histocompatibility complex, virus-related response (interferon-regulatory factor-1 and Mx) and lymphocyte markers (immunoglobulin M and T-cell receptor for B and T lymphocytes, respectively), as analysed by semi-quantitative reverse transcription-polymerase chain reaction, was up-regulated in the head-kidney of melatonin-injected fish 1 and 3 days postinjection and decreased after 7 days. These data, together with our previous observations describing how photoperiod and in vitro melatonin treatment may affect seabream and sea bass immunology, confirm melatonin as a regulator of fish immunology. However, further studies are still needed to reveal the mechanisms underlying the direct or indirect interactions of melatonin with the fish immune system.

Grass carp transforming growth factor-beta 1 (TGF-beta 1): molecular cloning, tissue distribution and immunobiological activity in teleost peripheral blood lymphocytes

Transforming growth factor-beta 1 (TGF-beta 1) is a potent regulatory cytokine with pleiotropic effects on the immune system. To examine the role of TGF-beta 1 in fish immunity, the full-length cDNA of grass carp TGF-beta 1 was isolated from grass carp spleen. The open reading frame of grass carp TGF-beta1, 1134 bp in length, encodes a 377 amino acid protein. Tissue distribution study by RT-PCR showed TGF-beta 1 mRNA was predominantly expressed in the thymus, head kidney and spleen in grass carp tissues. Moreover, the time-course effect of TGF-beta 1 on peripheral blood lymphocyte proliferation in response to mitogens was evaluated in grass carp. Interestingly, TGF-beta1 induced PBL proliferation while it significantly blocked phytohemagglutinin- or lipopolysaccharide-stimulated PBL proliferation, and TGF-beta 1 mimicked the stimulatory effects of lipopolysaccharide on grass carp MHC I mRNA expression. These results, for the first time, strongly suggest that TGF-beta 1 plays a functional role in lymphocyte proliferation in fish.