Major histocompatibility complex class IIA and IIB genes of Nile tilapia Oreochromis niloticus: genomic structure, molecular polymorphism and expression patterns

Efficacy of dietary Nano-selenium on growth, immune response, antioxidant, transcriptomic profile and resistance of Nile tilapia, Oreochromis niloticus against Streptococcus iniae infection

As recently applicable, there are few studies on the impact of using nano-selenium (nano-Se) on varied fish species. Where nothing reachable focused on its impact on tilapias so, the present analysis evaluated the efficacy of using nano-Se in tilapias on immune response, antioxidant defense compared by conventional Se form. 480 O. niloticus fingerlings were haphazardly grouped firstly into three groups with four replicates of each. The control one (CT) was fed on a basal diet. The second and third one supplemented with 0.7 mg/kg^-1 Se and nano-Se respectively for ten weeks. At the start day of the ninth week, two replicates from each group were injected by Streptococcus iniae where, the remaining replicates stand without challenge. Enhancement of growth performance measurements were noted in nano-Se compared to Se or CT groups. Existed anemia in S. iniae tilapias became alleviated by using nano-Se that also, improves the alteration of leucogram induced by challenge. Elevation of aminotransferases, alkaline phosphatase, lactate dehydrogenase (ALT, AST, ALP and LDH) and creatinine in Se and CT challenged replicates that seemed nearly normal by using nano-Se. Usage of nano-Se showed more powerful antioxidant activities than Se. There were an expansion of immunoglobulin M, lysozymes, glutathione peroxidase, nitric oxide, superoxide dismutase and catalase (IgM, LYZ, GPx, NO, SOD, CAT) and their related gene expression in nano-Se with contrast in Se or CT challenged groups. Nile tilapias challenged by S. iniae disclosed substantial expansion in the percentage of mortality in CT challenged fish (93.33%), followed by the group supplemented with Se (73.33%), whereas the lowermost one at fish supplemented by nano-Se (26.66%). The mortalities have been stopped from the 5^th, 12^th and 14^th days in, nano-Se, Se and CT respectively. It can be concluded that using of Se 0.7 mg/kg^-1induce immunosuppressive, antioxidant, liver and kidneys negative impact on tilapias where the same dose from nano-Se was more potent immunomodulating and antioxidant. Also it is attend in counteracting the serious impact induced by S. iniae challenge.

Immune-protective, antioxidant and relative genes expression impacts of β-glucan against fipronil toxicity in Nile tilapia, Oreochromis niloticus

Our study is considered to attempt reducing the immune-toxic and antioxidant impacts of exposure to fipronil (FP) on Nile tilapia, Oreochromis niloticus using the β-glucan (βG). Two hundred and seventy fingerlings of Nile tilapia were divided randomly into six groups (45 tilapias of each, in 3 replicates): group I control (CT) group nourished on a basal diet. Group II (βG) nourished a basal diet supplemented with 0.4% βG. Groups III (1/20 FP) and V (1/10 FP) was exposed to 1/20 and 1/10 of the 96 h LC₅₀ of FP in water and nourished the basal diet respectively. Groups IV (1/20 FP+ βG) and VI (1/10 FP+ βG) were exposed to 1/20 and 1/10 FP concomitantly with 0.4% βG supplementation for 90 successive days. Growth performance metrics were higher in βG group than CT. While those metrics were fallen at exposure to 1/20 or 1/10 FP. Supplementation with βG elevated the IgM and lysozyme levels.Whereas, tilapias exposed to FP only at different concentration showed lowering of those compared to CT. Supplementation with βG was effectively augmented IgM and lysozyme in 1/20 FP exposed tilapias. Furthermore, in a minor grade at 1/10 FP exposed tilapias. Exposure to FP increased the activities of hepatic markers chiefly at 1/10, however the βG supplementation was successfully improved these markers. There was imbalance of cortisol level at FP exposure where, βG combining to FP alleviate this disparity. There was fallen in LDH, MDH and FDPase in βG tilapias where continuing raise in 1/10 FP followed by 1/20 FP. βG supplementation raise the level of GSH, without significant variations in MDA conversely occurs in FP alone. Genes expression of βG caused raise of both GPx and GR, without fluctuations in CAT and SOD. Exposure to FP diminishes all evaluated antioxidant genes. It could fulfilled that supplementation with βG successfully alleviated the immune-toxic and antioxidant impact of FP in tilapias.

Effects of dietary anthocyanin on innate immune parameters, gene expression responses, and ammonia resistance of Nile tilapia (Oreochromis niloticus)

The present study investigated the effects of dietary anthocyanin on the growth performance, haematological, non-specific immune, and spleen gene expression responses of Nile tilapia, Oreochromis niloticus. Five experimental groups of fish with mean weights of 8.24 ± 0.64 g were used in the study; four of these were fed with diets incorporating anthocyanin (20 mg kg -¹, 40 mg kg^-1, 80 mg kg^-1 and 160 mg kg^-1), while the fifth was a control group without dietary anthocyanin. Growth performance and haematological parameters of tilapia were not affected by anthocyanin-supplemented diets (p > 0.05). Dietary anthocyanin significantly increased respiratory burst activity, phagocytic activity, phagocytic index, lysozyme activity, myeloperoxidase activity, serum total superoxide dismutase (T.SOD) activity, and serum catalase (CAT) activity (p < 0.05). The total immunoglobulin level was highest in the 80 mg kg^-1 group compared with the other groups (p < 0.05). In addition, with the anthocyanin-containing diets, the gene levels of interleukin 1, beta (IL-1β), interleukin 8 (IL-8), tumor necrosis factor (TNF-α), heat shock protein 70 (HSP70), and interferon gamma (IFN-γ) were increased in the fish spleen, and the gene levels of CAT, GPx, and SOD were also increased in fish liver (p < 0.05). At the end of the experiment, the fish were subjected to ammonia stress. The groups fed with 20 and 40 mg kg^-1 anthocyanin exhibited higher survival rates than the other groups. In summary, feeding Nile tilapia with anthocyanin-containing diets caused increases in the innate immune parameters, gene expression responses, and the survival rate of the fish subjected to ammonia stress.

Transcriptomic profile change, immunological response and disease resistance of Oreochromis niloticus fed with conventional and Nano-Zinc oxide dietary supplements

The present investigation was performed to evaluate the efficiency of Zinc oxide (ZnO) as a fish feed additive in immunomodulation of Oreochromis niloticus. Fish were fed on ZnO nano-particles (nZnO) and conventional (ZnO) in two concentrations (30 and 60 mg/kg diet), in addition to the control fish which was fed on Zn free diet. After 6° days, the highest survival rate was recorded in the nZnO₃₀ -supplemented group. The total antioxidant capacity (TAC) and antioxidant enzymes were improved in different dietary Zn supplementation, obviously in the nZnO₃₀ -supplemented group, while the lowest antioxidant status was noticed nZnO₆₀ supplemented fish. The lipid peroxides (MDA) level was diminished upon Zn supplementation, particularly in nZnO₃₀-supplemented group but showed a significant elevation in the nZnO₆₀-supplemented group. Furthermore, the immune parameters examined, lysozyme activity, bactericidal activity, and IgM were significantly higher in ZnO₆₀, and nZnO₃₀ supplemented groups. The C-reactive protein (CRP) level showed no significant increase in response to Zn supplementation in the both forms at level of 30 mg/kg diet, but showed marked elevation in nZnO₆₀- supplemented group. The mRNA expression profile of both interleukin 8 (IL-8), interleukin 1, beta (IL-1β) encoding genes showed an up-regulation that was found in all Zn- supplemented groups, but more pronounced in nZnO₆₀-supplemented group. On the other hand, the expression pattern of myxovirus resistance (Mx)-encoding gene showed no remarkable difference between the Zn- supplemented and control fish. The expression level of CXC-chemokine, toll-like receptor 7 (TLR-7), immunoglobulin M heavy chain (IgM heavy chain) and interferon gamma (IFN-γ) gene was upregulated in Zn-supplemented groups particularly in the nZnO₃₀- supplemented group. While, the lowest expression was found in nZnO₆₀- and ZnO₃₀-supplemented groups. Here, Zn supplementation promoted the immune and antioxidant strength in fish mainly in nano form at the level of 30 mg/kg diet but not at 60 mg/kg diet that disrupt the immune and antioxidant status and promote inflammatory response.

Screening of immuno-modulatory potential of different herbal plant extracts using striped catfish (Pangasianodon hypophthalmus) leukocyte-based in vitro tests

Many medicinal plants have been shown to possess biological effects, including immuno-modulatory activities on human and other mammals. However, studies about the potential mechanisms of plant extracts on the humoral and tissular immunities in fish have received less attention. This study aimed to screen the immunestimulating properties of 20 ethanol plant extracts on striped catfish Pangasianodon hypophthalmus leukocytes. The peripheral blood mononuclear cells (PBMCs) and head kidney leukocytes (HKLs) of striped catfish (50 ± 5 g per fish) were stimulated at 10 and 100 μg of each plant extract per mL of cell culture medium. Several humoral immune parameters (lysozyme, complement and total immunoglobulin) were examined at 24-h post stimulation (hps). Furthermore, the responses of four cytokine genes, namely il1β, ifrγ 2a and b, and mhc class II were assessed by quantitative real-time PCR at 6, 12, 24, and 48 hps. The results showed that lysozyme, complement as well as total immunoglobulin levels in both PBMCs and HKLs were regulated by some of the plant extracts tested in a concentration-dependent manner; some plant extracts induced the highest immune responses at the low dose (10 μg mL^-1) while others were more efficient at high dose (100 μg mL^-1). Among the extracts, five extracts including garlic Allium sativum L. (As), neem Azadirachta indica A. Juss (Ai), asthma-plant Euphorbia hirta L. (Eh), bhumi amla Phyllanthus amarus Schum. et Thonn (Pa), and ginger Zingiber officinale Rosc (Zo) induced significant changes in the expression of pro-inflammatory cytokine (il1β), antiviral cytokines (ifrγ 2a and b) and adaptive immune cytokine (mhc class II) in striped catfish cells. Pa always modulated the strongest expression of the four cytokines in PBMCs and HKLs over the whole experimental period (p < 0.05), whereas Zo did not stimulate the mhc class II expression in striped catfish leukocytes throughout experimental periods. These in vitro results demonstrated that some plant extracts could differently modulate great potential immune response in fish, supporting their applications in further in vivo experiments.

Effects of Cell Differentiation on the Phagocytic Activities of IgM+ B Cells in a Teleost Fish

Teleost B cells have phagocytic activities for ingesting particulate antigens, such as bacteria, in addition to the functional secretion of immunoglobulins (Igs). In the present study, the phagocytic activities of IgM⁺ B cells under various differentiational conditions residing in peripheral blood leukocytes were investigated in a teleost fish Nile tilapia (Oreochromis niloticus). The IgM⁺ B cells were recognized as IgM^lo or IgM^hi subsets based on their membrane IgM (mIgM) levels. The mIgM, secreted IgM (sIgM), major histocompatibility complex class II and reactive oxygen species were detected. Expressions of transcription factors (Pax5 and Blimp-1) and B cell signaling molecules (CD79a, CD79b, BLNK, and LYN) suggested that IgM^lo B cells were resembling as plasma-like cells and IgM^hi resembling as naïve/mature B cells, respectively. Analysis of phagocytic activities demonstrated that both IgM^lo and IgM^hi B cells have a similar phagocytic ability (phagocytosis percentage); however, the phagocytic capacity [phagocytic index and the mean fluorescence intensity (MFI)] of IgM^hi B cells was significantly higher than that of IgM^lo B cells. Taken together, the results indicated that B cell differentiation may cause the decrease of phagocytic capacity but not phagocytic ability of phagocytic IgM⁺ B cells in teleost. The finding may provide an evolutionary evidence for understanding the greater specialization of the B cell in more sophisticated adaptive humoral immunity, by decreasing phagocytic activity in order to contribute its function more specifically into antibody-secreting.

Optimum salinity for Nile tilapia (Oreochromis niloticus) growth and mRNA transcripts of ion-regulation, inflammatory, stress- and immune-related genes

We aim to study the optimum salinity concentration for Nile tilapia, through the assessment of its growth performance and the expression of its related genes (Gh and Igf-1), as well as its salinity adaptation and immune status through the assessment of the gene expression of ion-regulation genes (Na⁺/K⁺-ATPase α-1a and α-1b), stress-related genes (GST, HSP27, and HSP70), inflammatory-related genes (IL1, IL8, CC, and CXC chemokine), and immune-related genes (IgMH TLR7, MHC, and MX) at the osmoregulatory organs (gills, liver, and kidney). Based on the least mortality percentage and the physical appearance of the fish, three salt concentrations (6, 16, and 20 ppt) were chosen following a 6-month preliminary study using serial salt concentrations ranged from 6 to 36 ppt, which were obtained by rearing the fish in gradual elevated pond salinity through daily addition of 0.5 ppt saline water. The fish size was 10.2-12 cm and weight was 25.5-26.15 g. No significant differences in the fish weight gain were observed among the studied groups. The group reared at 16-ppt salt showed better performance than that of 20 ppt, as they have lower morality % and higher expression of ion-regulated gene (Na⁺/K⁺-ATPase α1-b), stress-related genes (GST, HSP27, and HSP70) of the gills and also GST, inflammatory-related genes (IL-1β and IL8), and TLR in the liver tissue. Higher expression of kidney-immune-related genes at 20-ppt salt may indicate that higher salinity predispose to fish infection and increased mortality. We concluded that 16-ppt salinity concentration is suitable for rearing O. niloticus as the fish are more adaptive to salinity condition without changes in their growth rate. Also, we indicate the use of immune stimulant feed additive to overcome the immune suppressive effect of hyper-salinity. Additionally, the survival of some fish at higher salinity concentrations (30-34 ppt) increase the chance for selection for salinity resistance in the Nile tilapia.

Molecular characterization and transcriptional expression of a B cell transcription factor Pax5 in Nile tilapia (Oreochromis niloticus)

Pax5 (Paired Box 5), a nuclear transcription factor expressed in B cell specifically, is a key regulator for B cell activation. In this study, we cloned and identified a Pax5 gene (OnPax5) from Nile tilapia (Oreochromis niloticus), which has an open reading frame of 1278 bp, encoding deduced amino acid sequence of 425 residues. OnPax5 contains a conserved DNA-binding domain encoding the paired box, an octapeptide, a homeobox homology region, a transactivation and a repressor domain. OnPax5 is constitutively expressed in various analyzed tissues of tilapia, with a relatively high expression in lymphoid organs, including spleen (SPL), anterior kidney (AK), and thymus. What's more, OnPax5 is highly expressed in leukocytes especially in IgM⁺ lymphocytes sorted from peripheral blood (PBL), SPL and AK. When stimulated with lipopolysaccharide (LPS) in vivo, OnPax5 expression was significantly up-regulated in PBL, SPL and AK. Upon stimulation with LPS, pokeweed mitogen and mouse anti-OnIgM monoclonal antibody in vitro, the expression of OnPax5 was also significantly up-regulated in leukocytes from SPL and AK. Taken together, Pax5, the B cell lineage specific activator factor, might get involved in B cell activation in Nile tilapia.

Association of MHC IIA polymorphisms with disease resistance in Aeromonas hydrophila-challenged Nile tilapia

The major histocompatibility complex (MHC) genes show high polymorphisms in vertebrates depending on animal immunity status. Herein, MHC class IIA gene in Aeromonas hydrophila-challenged Nile tilapia was screened for presence of polymorphisms using sequencing. Twelve nucleotides deletion polymorphism was determined with a PCR product size of 267 bp in the resistant fish and 255 bp in the control and susceptible/diseased fish. Additionally, a non-synonymous right frameshift c.712 T > G (P. 238 * > G) SNP was detected at the stop codon (*). SNP-susceptibility association analysis revealed that fish carrying GG genotype and allele G were high susceptible (risk) for A. hydrophila, and had lower immune response as indicated by significant reduction in non-specific immune parameters (total protein, globulin, IgM, phagocytic activity, phagocytic index, and lysosome activity) and mRNA level of MHC IIA, interleukin 1 beta (IL1β), tumor necrosis factor alfa (TNFα), and toll-like receptor 7 (TLR7) in the spleen and head kidney. Thus, G allele could be considered as a risk (recessive or mutant) allele for c. 712 T > G (P. 238 * > G) SNP and so selection of Nile tilapia with protective allele (T) for this SNP could improve the disease resistant of the fish.

Efficacy of an inactivated whole-cell injection vaccine for nile tilapia, Oreochromis niloticus (L), against multiple isolates of Francisella noatunensis subsp. orientalis from diverse geographical regions

Francisellosis, induced by Francisella noatunensis subsp. orientalis (Fno), is an emerging bacterial disease representing a major threat to the global tilapia industry. There are no commercialised vaccines presently available against francisellosis for use in farmed tilapia, and the only available therapeutic practices used in the field are either the prolonged use of antibiotics or increasing water temperature. Recently, an autogenous whole cell-adjuvanted injectable vaccine was developed that gave 100% relative percent survival (RPS) in tilapia challenged with a homologous isolate of Fno. In this study, we evaluated the efficacy of this vaccine against challenge with heterologous Fno isolates. Healthy Nile tilapia, Oreochromis niloticus (∼15 g) were injected intraperitoneally (i.p.) with the vaccine, adjuvant-alone or phosphate buffer saline (PBS) followed by an i.p. challenge with three Fno isolates from geographically distinct locations. The vaccine provided significant protection in all groups of vaccinated tilapia, with a significantly higher RPS of 82.3% obtained against homologous challenge, compared to 69.8% and 65.9% with the heterologous challenges. Protection correlated with significantly higher specific antibody responses, and western blot analysis demonstrated cross-isolate antigenicity with fish sera post-vaccination and post-challenge. Moreover, a significantly lower bacterial burden was detected by qPCR in conjunction with significantly greater expression of IgM, IL-1 β, TNF-α and MHCII, 72 h post-vaccination (hpv) in spleen samples from vaccinated tilapia compared to fish injected with adjuvant-alone and PBS. The Fno vaccine described in this study may provide a starting point for development a broad-spectrum highly protective vaccine against francisellosis in tilapia.

MHC Class IIB gene polymorphisms associated with resistance/susceptibility to Streptococcus agalactiae in Nile tilapia Oreochromis niloticus

Genetic variation in the major histocompatibility complex (MHC) Class IIB was tested in Nile tilapia Oreochromis niloticus, and the association between the MHC IIB alleles and disease resistance was also studied. F3 fry offspring (n = 1200) from 12 full-sib families were challenged with Streptococcus agalactiae, which caused significantly different mortalities in different Nile tilapia families (11.00-81.10%). Twenty fry (F1) from each of the 12 families were selected to study the polymorphisms of the MHC Class IIB gene using PCR followed by cloning and sequencing methods. The results showed that the size of the amplified fragment was 770-797 bp. Thirty-seven sequences from 240 individuals revealed 22 different alleles, which belonged to 9 major allele types. Up to 63.58% of nucleotide positions were variable, while the proportion of the amino acid variable positions was up to 68.73%. According to the survival rate of offspring (F3) from 12 full-sib families, we deduced that the alleles Orni-DAB*0107, Orni-DAB*0201 and Orni-DAB*0302 were highly associated with resistance to S. agalactiae, while the allele Orni-DAB*0701 was associated with susceptibility to S. agalactiae. In addition, our previous study found that the allele Orni-DAB*0201 was more frequently distributed in the disease-resistant groups. Therefore, the allele Orni-DAB*0201 could be used as an S. agalactiae resistance-related MHC marker in molecular marker-assisted selective breeding programs for S. agalactiae-resistant Nile tilapia.

Effects of dietary caffeic acid supplement on antioxidant, immunological and liver gene expression responses, and resistance of Nile tilapia, Oreochromis niloticus to Aeromonas veronii

The present study investigated the effects of dietary caffeic acid on haematological, serum biochemical, non-specific immune and liver gene expression responses of Nile tilapia, Oreochromis niloticus. Five experimental groups of fish with mean weights of 89.85 ± 2.5 g were used in the study; three of them were fed with caffeic acid incorporated diets (1 g kg^-1-Caf1, 5 g kg^-1-Caf5, 10 g kg^-1-Caf10), whereas an additive free basal diet served as the control. Additionally, the fifth group was an antibiotic medicated diet (0.02 g kg^-1-AMF), prepared with the florfenicol. Dietary caffeic acid especially at 5 g kg^-1 significantly increased phagocytic index, potential killing activity, respiratory burst activity, serum myeloperoxidase activity and serum catalase activity. Furthermore, increased levels of immune expression [heat shock protein 70 (HSP70), interleukin 1, beta (IL-1β), tumor necrosis factor (TNF-α), CC-chemokine (CC1), interleukin 8 (IL-8), toll-like receptor 7 (tlr-7), interferon gamma (IFN-γ) and immunoglobulin M (IgM)] and antioxidant related genes [superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx)] in the liver of fish fed with 5 g kg^-1 caffeic acid. At the end of the 20-day challenge period the survival rates were significantly higher in the Caf5 and AMF groups compared to all other treatment groups. As a result, feeding Nile tilapia with a diet containing 5 g kg^-1 caffeic acid over a period of 60 days might be adequate to improve fish immune parameters, antioxidant status, as well as survival rate against A. veronii, similar to antibiotic treatment. Thus caffeic acid can be suggested as a dietary substitute for antibiotic to prevent A. veronii in tilapia.

Effects of inosine 5'-monophosphate supplementation in high fishmeal and high soybean diets on growth, immune-related gene expression in gibel carp (Carassius auratus gibelio var. CAS Ⅲ), and its challenge against Aeromonas hydrophila infection

The present study was conducted to evaluate dietary inosine 5'-monophosphate (5'-IMP) on growth, immune genes expression and disease resistance against Aeromonas hydrophila in juvenile gibel carp (Carassius auratus gibelio var. CAS Ⅲ) (initial body weight: 7.48 g). Six diets were formulated containing exogenous 5'-IMP at three gradient levels (0, 0.1% and 0.2%) in the high dietary fishmeal group (15% fishmeal: D1, D2, D3) and in the high dietary soybean meal group (33% soybean meal: D4, D5, D6). Each diet was randomly allotted to triplicate tanks in a recirculating system. After the feeding trial, fish were exposed to Aeromonas hydrophila challenge. Hematological and immunological responses were analyzed before and after challenge. The results indicated that feeding rate in all 5'-IMP supplemented treatments (D2, D3, D5 and D6) and daily growth coefficient in D5 and D6 were reduced compared with those of respective control treatments (D1 and D4) without 5'-IMP addition (P < 0.05). The cumulative survival rates were numerically improved by dietary 5'-IMP supplementation (P > 0.05). Compared with the respective control treatment, in the high fishmeal group, plasma SOD and MPO were significantly elevated in D3 at the end of feeding trial (P < 0.05), plasma SOD and lysozyme were significantly increased in D3 after bacterial challenge (P < 0.05); in high soybean meal group, plasma lysozyme activity was significantly elevated in D5 post bacterial challenge (P < 0.05). Most of the expression of immune related genes (intelectin, major histocompatibility complex class II β (MHC II β), Complement 3 (C3), Complement component C7-1 (ccC7), lysozyme C, Interleukin 1β (IL-1β), Tumor necrosis factor α1 (TNF-α1), Transforming growth factor-beta (TGF-β) and Interleukin 8 (IL-8)) in spleen, kidney and liver of the fish were significantly affected by supplementation of 5'-IMP at the end of feeding trial and post bacterial challenge. Additionally, adding 5'-IMP in high soybean meal diets exerted further effects of promoting immunity than counterparts in high fishmeal diets. Considering enhanced disease resistance, the immunopotentiation of 5'-IMP was manifested when the addition level was 0.1% in high soybean meal diets and 0.2% in high fishmeal diets.

Effects of dietary blackberry syrup supplement on growth performance, antioxidant, and immunological responses, and resistance of Nile tilapia, Oreochromis niloticus to Plesiomonas shigelloides

The present study investigated the effects of dietary blackberry syrup on growth performance, haematological, non-specific immune and spleen gene expression responses of Nile tilapia, Oreochromis niloticus. Five experimental groups of fish with mean weights of 26.75 ± 2.67 g were used in the study; three of them were fed with blackberry syrup incorporated diets (7.5 g kg^-1- BBRY7.5, 15 g kg^-1- BBRY15, 30 g kg^-1- BBRY30), whereas an additive free basal diet served as the control. Additionally, the fifth group was an antibiotic medicated diet (0.02 g kg^-1- ABTC), prepared with the florfenicol. Dietary blackberry syrup especially at 15 g kg^-1 significantly increased growth performance, respiratory burst activity, potential killing activity, phagocytic activity, phagocytic index, lysozyme activity, myeloperoxidase activity, total immunoglobulin levels, serum SOD activity and serum CAT activity (p < 0.05). Furthermore, dietary blackberry syrup increased the expression levels of immune [heat shock protein 70 (HSP70), interleukin 1, beta (IL-1β), tumor necrosis factor (TNF-α), interferon gamma (IFN-γ), immunoglobulin M (IgM)] and antioxidant [glutathione peroxidase (GPx)] related genes in the spleen of fish fed with especially 15 g kg^-1 blackberry syrup (p < 0.05). At the end of the 20-day challenge period the survival rates were significantly higher in the BBRY15 and ABTC groups compared to all other treatment groups (p < 0.05). As a result, feeding Nile tilapia with a diet containing 15 g kg^-1 blackberry syrup over a period of 90 days might be adequate to improve growth performance, fish immune parameters, antioxidant status, as well as survival rate against P. shigelloides, similar to antibiotic treatment. Hence, blackberry syrup can be used as an antibiotics replacer for controlling P. shigelloides in tilapia feed.

MHC class IIA polymorphisms and their association with resistance-susceptibility to Streptococcus agalactiae in Nile tilapia, Oreochromis niloticus

The association between major histocompatibility complex (MHC) class IIA polymorphisms and the severity of infection by Streptococcus agalactiae was investigated using 40 susceptible and 40 resistant individuals of Nile tilapia Oreochromis niloticus. Twenty-five alleles were identified from 80 individuals, which belong to 22 major allele types. High polymorphism of mhcIIa gene and at least two loci were discovered in O. niloticus. In peptide-binding region (PBR) and non-PBR, the ratio of nonsynonymous substitution (dN) to synonymous substitution (dS) was 1.294 (>1) and 1.240 (>1), suggesting that the loci are evolving under positive balancing selection. Association analysis showed that the allele, orni-daa*0501, was significantly associated with resistance to S. agalactiae, while the alleles, orni-daa*1101, orni-daa*1301, orni-daa*1401 and orni-daa*1201, were associated with susceptibility to S. agalactiae. To confirm these correlations, another independent challenge experiment was performed in the Huizhou population of the O. niloticus. The frequency distribution showed that the orni-daa*1101 allele was significantly more frequent in the Huizhou-Susceptible group (HZ-SG) than in the Huizhou-Resistant group (HZ-RG) (P < 0.05), which was consistent with the first challenge. However, orni-daa*0501 did not present in HZ-SG and HZ-RG and the distribution frequencies of the orni-daa*1201, orni-daa*1301 and orni-daa*1401 alleles were not significantly more frequent in HZ-SG than in HZ-RG. These results indicate that the orni-daa*1101 allele confers susceptibility to S. agalactia infection. These results suggest that the diversity of exon 2 of mcaIIa alleles could be used to explore the association between disease susceptibility or resistance and the multiformity of mcaIIa and to achieve the molecular-assisted selection of O. niloticus with enhanced disease resistance.

Molecular characterization and function analysis of three RIG-I-like receptor signaling pathway genes (MDA5, LGP2 and MAVS) in Oreochromis niloticus

The recognition of microbial pathogens, which is mediated by pattern recognition receptors (PRRs), is critical to the initiation of innate immune responses. In the present study, we isolated the full-length cDNA and genomic DNA sequences of the MDA5, LGP2 and MAVS genes in Nile tilapia, termed OnMDA5, OnLGP2 and OnMAVS. The OnMDA5 gene encodes 974 amino acids and contains two caspase-associated recruitment domains (CARDs), a DExDc domain (DExD/H box-containing domain), a HELICc (helicase superfamily C-terminal) domain and a C-terminal regulatory domain (RD). The OnLGP2 gene encodes 679 amino acids and contains a DExDc, a HELICc and an RD. The OnMAVS gene encodes 556 amino acids and contains a CARD, a proline-rich domain, a transmembrane helix domain and a putative TRAF2-binding motif (269PVQDT273). Phylogenetic analyses showed that all three genes from Nile tilapia were clustered together with their counterparts from other teleost fishes. Real-time PCR analyses showed that all three genes were constitutively expressed in all examined tissues in Nile tilapia. OnMDA5 presented the highest expression level in the blood and the lowest expression level in the liver, while OnMAVS presented the highest expression level in the kidney. The highest expression level of OnLGP2 was detected in the liver. An examination of the expression patterns of these RIG-I-like receptors (RLRs) during embryonic development showed that the highest expression levels of OnMDA5 occurred at 2 days postfertilization (dpf), and the expression significantly decreased from 3 to 8 dpf. The expression levels of OnLGP2 significantly increased from 4 to 8 dpf. The expression levels of OnMAVS mRNA were stable from 2 to 8 dpf. Upon stimulation by intraperitoneal injection of Streptococcus agalactiae, the expression levels of OnMDA5 were first downregulated and then upregulated in the blood, gill and spleen. In the intestine and kidney, the expression of OnMDA5 was first upregulated, then downregulated, and then upregulated again. The expression of OnLGP2 was upregulated in the kidney and intestine, and the expression of OnMAVS was upregulated in the spleen. Overexpression of OnMAVS increased NF-κB activation in 293 T cells (p < 0.05), and after cotransfection with OnMDA5, the OnMAVS-dependent NF-κB activation was slightly increased (p > 0.05), after cotransfection with OnLGP2, the OnMAVS-dependent NF-κB activation was significantly decreased (p < 0.05). These findings suggest that, although the deduced protein structure of OnMDA5 is evolutionarily conserved with the structures of other RLR members, its signal transduction function is markedly different. The results also suggest that OnLGP2 has a negative regulatory effect on the OnMAVS gene. OnMDA5 and OnMAVS were uniformly distributed throughout the cytoplasm in 293 T cells, whereas OnLGP2 was distributed throughout the cytoplasm and nucleus. These results are helpful for clarifying the innate immune response against bacterial infection in Nile tilapia.

Immune-Related Transcriptional Responses to Parasitic Infection in a Naturally Inbred Fish: Roles of Genotype and Individual Variation

Parasites are strong drivers of evolutionary change and the genetic variation of both host and parasite populations can co-evolve as a function of parasite virulence and host resistance. The role of transcriptome variation in specific interactions between host and parasite genotypes has been less studied and can be confounded by differences in genetic variation. We employed two naturally inbred lines of a self-fertilizing fish to estimate the role of host genotype in the transcriptome response to parasite infection using RNA-seq. In addition, we targeted several differentially expressed immune-related genes to further investigate the relative role of individual variation in the immune response using RT-qPCR, taking advantage of the genomic uniformity of the self-fertilizing lines. We found significant differences in gene expression between lines in response to infection both in the transcriptome and in individual gene RT-qPCR analyses. Individual RT-qPCR analyses of gene expression identified significant variance differences between lines for six genes but only for three genes between infected and control fish. Our results indicate that although the genetic background plays an important role in the transcriptome response to parasites, it cannot fully explain individual differences within genetically homogeneous lines, which can be important for determining the response to parasites.

MHC class IIα polymorphism and its association with resistance/susceptibility to Vibrio harveyi in golden pompano (Trachinotus ovatus)

The major histocompatibility complex (MHC) plays an important role in the vertebrate immune response to antigenic peptides, and it is essential for recognizing foreign pathogens in organisms. In this study, MHC class IIα (Trov-MHC IIα) from the golden pompano (Trachinotus ovatus) was first cloned and identified. The gene structure of Trov-MHC IIα was contained four exons and three introns. High levels of polymorphism were found in the exon 2 of Trov-MHC IIα. A total of 29 different MHC class IIα alleles with high polymorphism were identified from 80 individuals. The ratio of non-synonymous substitutions (dN) to synonymous substitutions (dS) was 3.157 (>1) in the peptide binding regions (PBRs) of Trov-MHC IIα, suggesting positive balancing selection. Six alleles were selected to analyze the association between alleles and resistance/susceptibility to Vibrio harveyi in golden pompano. The results showed that Trov-DAA*6401 and Trov-DAA*6702 alleles were associated with the resistance to V. harveyi in golden pompano, while alleles Trov-DAA*6304 and Trov-DAA*7301 were associated with the susceptibility to V. harveyi in golden pompano. This study confirmed the association between alleles of MHC class IIα and disease resistance, and also detected some alleles which might be correlated with high V. harveyi-resistance. These disease resistance-related MHC alleles could be used as potential genetic markers for molecular marker-assisted selective breeding in the golden pompano.

Characterization and expression of Na+/K+-ATPase in gills and kidneys of the Teleost fish Oreochromis mossambicus, Oreochromis urolepis hornorum and their hybrids in response to salinity challenge

Tilapia (Oreochromis mossambicus, O. urolepis hornorum, their hybrids O. mossambicus♀ × O. hornorum♂ and O. hornorum♀ × O. mossambicus♂) were exposed to a high salinity environment to evaluate their osmoregulatory responses. The plasma osmolality of all the tilapia species were elevated with the salinity challenge. The activities of Na⁺/K⁺-ATPase (NKA) in both the gill and kidney showed a similar increased change tendency compared with the control. The distribution of NKA α1 mRNA in all the examined tissues suggested that NKA α1 has a possible housekeeping role for this isoform. The amount of NKA α1 mRNA in the gill and kidney was elevated in the four fishes with similar expression patterns after transfer from freshwater to seawater. The NKAα1 mRNA expression levels in the gill reached their peak level at 24 h after transfer (P < 0.01) compared to the freshwater group, following decreases in the pretreatment level at 48 h (P > 0.05). However, the NKAα1 mRNA expression levels in the kidney were not significantly affected with increasing environmental salinity (P > 0.05). The differences in the responses to saltwater challenge may be associated with differences in saltwater tolerance between the four tilapia. The drastic increase in the plasma osmolality, NKA activities and mRNA expression suggested that the hybrids (O. mossambicus♀ × O. hornorum♂) possess heterosis in salinity responsiveness compared to that of both the parents, indicating a maternal effect on the salinity tolerance of the tilapia hybrids. This study provides a theoretical basis to further study the mechanism of fish osmoregulation response to salinity challenge.

Molecular identification of Trichodina compacta Van As and Basson, 1989 (Ciliophora: Peritrichia) from cultured Oreochromis niloticus in Egypt and its impact on immune responses and tissue pathology

Trichodinids are peritrichous ciliated protozoa that affect both wild and cultured fishes. Several Trichodina species have low host specificity and are morphologically distinct, facilitating their identification based primarily on the presence of adhesive discs and the number of attached denticles. A trichodinid species named Trichodina compacta was first reported by Van As and Basson (1989) (Protozoa: Ciliophora: Peritrichia). However, in trichodinid infestations, morphological characteristics are insufficient for identifying the infesting species. Therefore, molecular and phylogenetic analyses are considered to be promising and useful tools for identifying the infesting species. This study aimed to achieve the molecular identification of a trichodinid infestation in Nile tilapia and to construct the phylogenetic relationships between the identified species and other peritrichous parasites. Moreover, we also aimed to study the pathological and immunological impacts of trichodinids on fry tissue to improve our understanding of the immune responses of teleost fish to trichodinae parasitic infestations and develop a better control method. Here, we used molecular techniques to identify the isolated trichodina species as T. compacta and demonstrated that Trichodina infestation in Nile tilapia is associated with remarkable immunogenic and inflammatory responses (increased il-1β expression and decreased il-8 and tgf-β expression). These findings improve our understanding of the responses of teleost fish to trichodinid parasite infestation and will be helpful for the development of novel control strategies that reverse the inflammatory and immunogenic alterations that occur in infested fish.

Characterization of type IV antifreeze gene in Nile tilapia (Oreochromis niloticus) and influence of cold and hot weather on its expression and some immune-related genes

The aim of this work is to study the effect of the thermal stress of ambient temperature during winter and summer on the expression of type IV antifreeze gene (ANF IV) in different tissues of Nile tilapia (Oreochromis niloticus) as well as some immune-related genes. At first, genomic ANF IV gene was characterized from one fish; 124 amino acids were identified with 92.7% similarity with that on the gene bank. Expression of ANF IV and immune-related genes were done twice, once at the end of December (winter sample, temperature 14 °C) and the other at August (summer sample, temperature 36 °C). Assessment of ANF IV gene expression in different organs of fish was done; splenic mRNA was used for assessment of immune-related gene transcripts (CXCl2 chemokine, cc-chemokine, INF-3A, and MHC IIβ). Winter expression analysis of AFP IV in O. niloticus revealed significant upregulation of mRNA transcript levels in the intestine, gills, skin, spleen, liver, and brain with 324.03-, 170.06-, 107.63-, 97.61-, 94.35-, and 27.85-folds, respectively. Furthermore, upregulation in the gene was observed in some organs during summer: in the liver, gills, skin, intestine, and brain with lower levels compared with winter. The level of expression of immune-related genes in winter is significantly higher than summer in all assessed genes. Cc-chemokine gene expression was the most affected in both winter and summer. Variable expression profile of ANF IV in different organs and in different seasons together with its amino acid similarity of N-terminal and C-terminal with apolipoprotein (lipid binder) and form of high-density lipoprotein (HDL) suggests a different role for this protein which may be related to lipid metabolism.

Molecular characterization, expression and functional analysis of NOD1, NOD2 and NLRC3 in Nile tilapia (Oreochromis niloticus)

The nucleotide-binding oligomerization domain proteins NOD1, NOD2 and NLRC3 are cytoplasmic pattern recognition receptors (PRRs) of the Nod-like receptor (NLR) family. In the present study, the Nile tilapia (Oreochromis niloticus) NOD1 (ntNOD1), NOD2 (ntNOD2) and NLRC3 (ntNLRC3) genes were cloned and characterized. The full-length ntNOD1, ntNOD2 and ntNLRC3 genes were 3924, 3886 and 4574 bp, encoding 941, 986 and 1130 amino acids, respectively. The three Nod-like receptors have a NACHT domain and a C-terminal leucine-rich repeat (LRR) domain. In addition, ntNOD1 and ntNOD2 have a N-terminal CARD domain (ntNOD2 has two). Phylogenetic analysis showed that the three NLRs are highly conserved. Tissue expression analysis of the three receptors revealed that the highest mRNA and protein levels of ntNOD1, ntNOD2 and ntNLRC3 were in the spleen. The expression patterns of NLRs during embryonic development showed that the expression levels of ntNOD2 and ntNLRC3 significantly increased from 2 to 8 days post-fertilization (dpf). The expression levels of ntNOD1 significantly increased from 2 to 6 dpf, decreased at 7 dpf and then increased at 8 dpf. Upon stimulation with an intraperitoneal injection of Streptococcus agalactiae, expression levels of the ntNOD1, ntNOD2 and ntNLRC3 mRNA and protein were clearly altered in the blood, spleen, kidney, intestine and gill. Furthermore, after cotransfection with an NF-κB reporter plasmid, NF-κB activation in ntNOD1-overexpressing 293T cells significantly increased compared with that in control cells, before or after i-EDPA-stimulation. By contrast, compared with control, ntNOD2 and ntNLRC3 had no effect on NF-κB activation in 293T cells, when their potential ligands were not stimulated. However, after MDP-stimulation, ntNOD2 and ntNLRC3 overexpression increased NF-κB activation in 293T cells. NOD1 and NLRC3 were uniformly distributed throughout the cytoplasm in 293T cells, whereas NOD2 was distributed throughout the cytoplasm and nucleus. Our results indicate that the three Nod-like receptors are functionally conserved and may play pivotal roles in defense against pathogens such as Streptococcus agalactiae.

MHC class II alpha, beta and MHC class II-associated invariant chains from Chinese sturgeon (Acipenser sinensis) and their response to immune stimulation

The major histocompatibility complex class II (MHC II) molecules play a vital role in adaptive immune response through presenting antigenic peptides to CD4⁺ T lymphocytes. To accomplish this physiologic function, the MHC class II-associated invariant chain interacts with the MHC II α/β subunits and promotes their correct assembly and efficient traffic. Here, we isolated the cDNAs of MHC II α, β and MHC II-associated invariant chains (designated as CsMHC II α, CsMHC II β, and CsMHC II γ) from Chinese sturgeon (Acipenser sinensis). The CsMHC II α, β, and γ mRNAs were widely expressed in Chinese sturgeon, and the highest expression was found in spleen for CsMHC II α and β chains, while in head kidney for CsMHC II γ chain. Stimulation to Chinese sturgeon with inactivated trivalent bacterial vaccine or polyinosinic polycytidylic acid (poly(I:C)) up-regulated the expressions of CsMHC II α, and β mRNAs, and their transcripts were overall more quickly up-regulated by poly(I:C) than by bacterial vaccine. Poly(I:C) induced higher CsMHC II γ expression than bacterial vaccine in intestine and spleen, while lower than bacterial vaccine in head kidney and liver. When co-expressed in mouse dendritic cells, the CsMHC II γ chain bound to both the MHC II α and β chains. Furthermore, the over-expressed CsMHC II γ chain, not CsMHC II α or CsMHC II β chain, activated NF-κB and STAT3 in mouse dendritic cells, and induced TNF-α and IL-6 expressions as well. This activity was nearly abolished by mutation of the Ser29/Ser34 to Ala29/Ala34 in CsMHC II γ. These results suggested that CsMHC II α, β, and γ chains might play important role in immune response to pathogen microbial infection of Chinese sturgeon possibly via a conserved functional mechanism throughout vertebrate evolution, which might contribute to our understanding the immune biology of sturgeons.

Modulatory effect of different doses of β-1,3/1,6-glucan on the expression of antioxidant, inflammatory, stress and immune-related genes of Oreochromis niloticus challenged with Streptococcus iniae

β-glucans are widely-known immunostimulants that are profusely used in aquaculture industry. The present study was conducted to evaluate the effect of different in-feed doses of β-1,3/1,6-glucans on the expression of antioxidant and stress-related genes (GST, HSP-70, Vtg), inflammation related genes (Il-8, TNFα, CXC-chemokine and CAS) and adaptive immune-related genes (MHC-IIβ, TLR-7, IgM-H, and Mx) of Oreochromis niloticus challenged and non-challenged with Streptococcus iniae. Six experimental groups were established: non-challenged control (non-supplemented diet), challenged control (non-supplemented diet), non-challenged supplemented with 0.1% β-glucan, challenged supplemented with 0.1% β-glucan, non-challenged supplemented with 0.2% β-glucan and challenged supplemented with 0.2% β-glucan. Fish were fed with β-glucan for 21 days prior challenge and then sampled after 1, 3 and 7 days post-challenge. In non-challenged group, variable effects of the two doses of β-Glucans on the expression of the studied genes were observed; 0.1% induced higher expression of HSP70, CXC chemokine, MHC-IIβ and MX genes. Meanwhile, 0.2% induced better effect on the expression of Vtg, TNF-α, CAS and IgM-H, and almost equal effects of both doses on GST and IL8. However, with the challenged group, 0.2% β-Glucans showed better effect than 0.1% at day one post challenge through significant up-regulation of GST, HSP, IL8, TNF-α, CXC, and MHC-IIβ, meanwhile, the effect of 0.1% was only on the expression of HSP70, MHC-IIβ, and TLR7 at day 3 post challenge. No stimulatory role for both doses of β-Glucans on the expression of almost all genes at day 7 post-challenge. We conclude that both doses of β-glucan can modulate the antioxidant, inflammation, stress and immune-related genes in Nile tilapia, moreover, 0.2% β-Glucans showed better protective effect with Streptococcus iniae challange.

Assessment of complex water pollution with heavy metals and Pyrethroid pesticides on transcript levels of metallothionein and immune related genes

Alteration of immunological function of an aquatic organism can be used as an indicator for evaluating the direct effect of exposure to pollutants. The aim of this work is to assess the impact of complex water pollution with special reference to Pyrethroid pesticides and heavy metals on mRNA transcript levels of Metallothionine and some immune related genes of Nile tilapia (Oreochromas Niloticus). Residues of six heavy metals and six Pyrethroid were assessed in water as well as fish tissues at three different sites of Lake Burullus, located at Northern Egypt. Variations of water physicochemical properties associated with different levels of heavy metals at the three different sections were recorded. Tissue residues of Fe, Mn and Zn, Cu, Ni exceed water levels in contrast to elevated water level of Pb. All assessed Pyrethroids are detected in fish tissue samples with higher concentration (3-42 folds) than that found in water samples especially Cypermethrin. Significant down-regulation of expression levels of metallothionein (MT) at the three sections of the lake was observed. The expression of immune related genes (IgM) and inflammatory cytokines (TNF, IL.8 and IL.1) were affected. IgM and TNF were significantly down-regulated at eastern and western section of the lake; meanwhile the expression of IL8 is down regulated at the three sections of the lack. IL1 was significantly up-regulated at eastern and middle sections. We conclude that, variable gene expression of MT and immune-related genes at the three sections of the lack impose different response to complex water pollution in relation to variable aquatic environment.

Identification, polymorphism and expression of MHC class Iα in golden pompano, Trachinotus ovatus

The classical major histocompatibility complex class I (MHC I) plays a vital role in the immune system. In this study, we cloned and identified golden pompano (Trachinotus ovatus) MHC Iα (Trov-MHC Iα), which encodes 351 amino acid residues including a leader peptide, α1, α2, α3 domain, a transmembrane region and a cytoplasmic domain. Twenty six different sequences, which encoded various numbers of amino acid residues ranging from 348 to 354, were obtained from 12 individuals. Highly genetic polymorphism was found in the Trov-MHC Iα, especially in the α1 and α2 domains. Meanwhile, in the α1 and α2 domains, 21 positive selected positions were revealed by site models, indicating the diversity of Trov-MHC Iα may be mainly generated by positive selection. Moreover, quantitative real-time reverse transcription PCR and western blotting analyses demonstrated that Trov-MHC Iα was ubiquitously expressed in the nine tested tissues and more highly expressed in intestine, head kidney, gill, and spleen. In the head kidney and spleen, Trov-MHC Iα was significantly upregulated under LPS or poly I:C stimulation. The results of this study provide valuable insight into molecular polymorphism, evolutionary mechanism, expression and function of MHC Iα in the immune system of golden pompano.

Impaired antioxidant gene expression by pesticide residues and its relation with other cellular biomarkers in Nile Tilapia (Oreochromis niloticus) from Lake Burullus

Organochlorines and Organophosphorus are the most commonly used pesticides. These pesticides constitute a considerable contaminating threat due to their excessive agricultural usage which in turn contaminates the aquatic system through agricultural drainage. The aim of this study was to evaluate water and tissue residues of both pesticides in O. niloticus obtained from three different sections in Lake Burullus, Egypt. Assessment of relative change in mRNA levels of GST and Vtg (oxidative stress indicator) was done and its relation with other cellular biomarkers including apoptosis, which is assessed by Cellular apoptosis susceptibility transcript level (CAS), comet assay and micronucleus assays (genotoxicity indicator). Pesticide residue levels in water are fluctuating. In fish tissues, most residues were higher than those found in water and were associated with down regulation of hepatic GST gene and Vtg expression. CAS gene involved in apoptosis, its transcript is down regulated in middle and western sections of the lake with higher pesticide residues. Different degrees of DNA damages in O. niloticus' liver cells were demonstrated by comet assay. Significant increase in the micronucleated cells in the three sections of the lake was observed; the western section fish showed the highest number. Persistent exposures of fish to pesticide caused impairment of antioxidant gene expression. This negatively affects apoptosis associated with damaging DNA and chromosome fragments.

Molecular characterization of MHC class IIB genes of sympatric Neotropical cichlids

BACKGROUND

The Major Histocompatibility Complex (MHC) is a key component of the adaptive immune system of all vertebrates and consists of the most polymorphic genes known to date. Due to this complexity, however, MHC remains to be characterized in many species including any Neotropical cichlid fish. Neotropical crater lake cichlids are ideal models to study evolutionary processes as they display one of the most convincing examples of sympatric and repeated parallel radiation events within and among isolated crater lakes.

RESULTS

Here, we characterized the genes of MHC class IIB chain of the Midas cichlid species complex (Amphilophus cf. citrinellus) including fish from five lakes in Nicaragua. We designed 19 new specific primers anchored in a stepwise fashion in order to detect all alleles present. We obtained 866 genomic DNA (gDNA) sequences from thirteen individuals and 756 additional sequences from complementary DNA (cDNA) of seven of those individuals. We identified 69 distinct alleles with up to 25 alleles per individual. We also found considerable intron length variation and mismatches of alleles detected in cDNA and gDNA suggesting that some loci have undergone pseudogenization. Lastly, we created a model of protein structure homology for each allele and identified their key structural components.

CONCLUSIONS

Overall, the Midas cichlid has one of the most diverse repertoires of MHC class IIB genes known, which could serve as a powerful tool to elucidate the process of divergent radiations, colonization and speciation in sympatry.

The extent to which immunity, apoptosis and detoxification gene expression interact with 17 alpha-methyltestosterone

Innate immunity is the first line of defence against invasion by foreign pathogens. One widely used synthetic androgen for the production of all-male fish, particularly commercially valuable Nile tilapia, Oreochromis niloticus, is 17 alpha-methyltestosterone (MT). The present study investigates the effect of MT on innate immunity, cellular apoptosis and detoxification and the mortality rate, during and after the feeding of fry with 0-, 40-and 60-mg MT/kg. Expression analysis was completed on interleukin 1 beta (il1β), interleukin 8 (il8), tumour necrosis factor alpha (tnfα), CXC2- and CC-chemokines, interferon (ifn), myxovirus resistance (mx), toll-like receptor 7 (tlr7), immunoglobulin M heavy chain (IgM heavy chain), vitellogenin (vtg), cellular apoptosis susceptibility (cas) and glutathione S-transferase α1 (gstα1). Expression analysis revealed that MT had a significant impact on these genes, and this impact varied from induction to repression during and after the treatment. Linear regression analysis showed a significant association between the majority of the tested gene transcript levels and mortality rates on the 7^th and 21^st days of hormonal treatment and 2 weeks following hormonal cessation. The results are thoroughly discussed in this article. This is the first report concerning the hazardous effect of MT on a series of genes involved in immunity, apoptosis and detoxification in the Nile tilapia fry.

Genomic structure and expression pattern of MHC IIα and IIβ genes reveal an unusual immune trait in lined seahorse Hippocampus erectus

The major histocompatibility complex (MHC) genes are crucial in the adaptive immune system, and the gene duplication of MHC in animals can generally result in immune flexibility. In this study, we found that the lined seahorse (Hippocampus erectus) has only one gene copy number (GCN) of MHC IIα and IIβ, which is different from that in other teleosts. Together with the lack of spleen and gut-associated lymphatic tissue (GALT), the seahorse may be referred to as having a partial but natural "immunodeficiency". Highly variable amino acid residues were found in the IIα and IIβ domains, especially in the α1 and β1 domains with 9.62% and 8.43% allelic variation, respectively. Site models revealed seven and ten positively selected positions in the α1 and β1 domains, respectively. Real-time PCR experiments showed high expression levels of the MHC II genes in intestine (In), gill (Gi) and trunk kidney (TK) and medium in muscle (Mu) and brood pouch (BP), and the expression levels were significantly up-regulated after bacterial infection. Specially, relative higher expression level of both MHC IIα and IIβ was found in Mu and BP when compared with other fish species, in which MHC II is expressed negligibly in Mu. These results indicate that apart from TK, Gi and In, MU and BP play an important role in the immune response against pathogens in the seahorse. In conclusion, high allelic variation and strong positive selection in PBR and relative higher expression in MU and BP are speculated to partly compensate for the immunodeficiency.

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.

Immunity to nervous necrosis virus infections of orange-spotted grouper (Epinephelus coioides) by vaccination with virus-like particles

Nervous necrosis virus (NNV) is a kind of the betanodaviruses, which can cause viral nervous necrosis (VNN) and massive mortality in larval and juvenile stages of orange-spotted grouper (Epinephelus coioides). Due to the lack of viral genomes, virus-like particles (VLPs) are considered as one of the most promising candidates in vaccine study to control this disease. In this study, a type of VLPs, which was engineered on the basis of orange-spotted grouper nervous necrosis virus (OGNNV), was produced from prokaryotes. They possessed the similar structure and size to the native NNV. In addition, synthetic oligodeoxynucleotide (ODN) containing CpG motif was added in vaccines, and the expression patterns of several genes were analyzed after injecting with VLP and VLP with adjuvant (VA) to assess the regulation effect of vaccine for inducing immune responses. RT-PCR assays showed that six related genes in healthy tissues were ubiquitously expressed in all nine tested tissues. The vaccine alone was able to enhance the expression of genes, including MHCIa, MyD88, TLR3, TLR9 and TLR22 after vaccination, indicating that the vaccine was able to induce immune response in grouper. In liver, spleen and kidney, the gene expressions of VA group were all significantly higher than that of VLP group at 72 h post-stimulation, showing that the fish of VA challenge group obtained the longer-lasting protective immunity and resistance to pathogen challenge than that of VLP group. The data indicated that the efficacy of vaccine could be further enhanced by CpG ODN after vaccination and provided the reference for the development of future viral vaccine in grouper.

Identification of 48 full-length MHC-DAB functional alleles in miiuy croaker and evidence for positive selection

Major histocompatibility complex (MHC) molecules play a vital role in the immune response and are a highly polymorphic gene superfamily in vertebrates. As the molecular marker associated with polymorphism and disease susceptibility/resistance, the polymorphism of MHC genes has been investigated in many tetrapods and teleosts. Most studies were focused on the polymorphism of the second exon, which encodes the peptide-binding region (PBR) in the α1- or β1-domain, but few studies have examined the full-length coding region. To comprehensive investigate the polymorphism of MHC gene, we identified 48 full-length miiuy croaker (Miichthys miiuy) MHC class IIB (Mimi-DAB) functional alleles from 26 miiuy croaker individuals. All of the alleles encode 34 amino acid sequences, and a high level of polymorphism was detected in Mimi-DAB alleles. The rate of non-synonymous substitutions (dN) occurred at a significantly higher frequency than that of synonymous substitutions (dS) in the PBR, and this result suggests that balancing selection maintains polymorphisms at the Mimi-DAB locus. Phylogenetic analysis based on the full-length and exon 2 sequences of Mimi-DAB alleles both showed that the Mimi-DAB alleles were clustered into two major groups. A total of 19 positive selected sites were identified on the Mimi-DAB alleles after testing for positive selection, and 14 sites were predicted to be associated with antigen-binding sites, which suggests that most of selected sites are significant for disease resistance. The polymorphism of Mimi-DAB alleles provides an important resource for analyzing the association between the polymorphism of MHC gene and disease susceptibility/resistance, and for researching the molecular selective breeding of miiuy croaker with enhanced disease resistance.

Trancriptomic profiling revealed the signatures of acute immune response in tilapia (Oreochromis niloticus) following Streptococcus iniae challenge

Streptococcus iniae is the most significant bacterial disease of tilapia throughout the world, and commonly leads to tremendous economic losses. In contrast to other important fish species, our knowledge about the molecular mechanisms of tilapia in response to bacterial infection is still limited. Here, therefore, we utilized RNA-seq to first profiling of host responses in tilapia spleen following S. iniae infection at transcriptome level. A total of 223 million reads were obtained and assembled into 192,884 contigs with average length 844 bp. Gene expression analysis between control and infected samples at 5 h, 50 h, and 7 d revealed 1475 differentially expressed genes. In particular, the differentially expressed gene set was dramatically induced as early as 5 h, and rapidly declined to basal levels at 50 h. Enrichment and pathway analysis of the differentially expressed genes revealed the centrality of the pathogen attachment and recognition, cytoskeletal rearrangement and immune activation/inflammation in the pathogen entry and host inflammatory responses. Understanding of these responses can highlight mechanisms of tilapia host defense, and expand our knowledge of teleost immunology. Our findings will set a foundation of valuable biomarkers for future individual, strain, and family-level studies to evaluate immune effect of vaccine and individual response in host defense mechanisms to S. iniae infection, to select disease resistant families and strains.

Molecular cloning and expression analysis of major histocompatibility complex class I, IIA and IIB genes of blunt snout bream (Megalobrama amblycephala)

Major histocompatibility complex (MHC) plays an important role in the immune response of vertebrates. In this study, we isolated MHC class IIA and IIB genes from blunt snout bream (Megalobrama amblycephala) by rapid amplification of cDNA ends polymerase chain reaction (RACE-PCR). In order to study the function of the MHC genes in M. amblycephala, tissue distribution and immune response of the MHC genes to bacterial challenge were analyzed. All the characteristic features of MHC class II chain structure could be identified in the deduced amino sequences of MHC IIA and IIB, including the leader peptide, α1/β1 and α2/β2 domains, connecting peptide and transmembrane and cytoplasmic regions, as well as conserved cysteines and N-glycosylation site. The deduced amino acid sequence of the MHC IIA and IIB molecules shared from 48% to 88% and from 65% to 77% similarity with those of other teleosts, respectively. Quantitative real-time PCR (qRT-PCR) demonstrated that MHC I and II genes were ubiquitously expressed in ten tissues, with high level in immune related tissues, including kidney, intestine, gill and spleen. Challenge of M. amblycephala with the extracellular pathogen, Aeromonas hydrophila, resulted in a significant increase in the expression of MHC I, MHC IIA and IIB mRNA within 72 h after infection in gill, kidney, intestine and liver, followed by a recovery to normal level after 120 h. The changes of expression levels for MHC IIA and IIB in most tissues were significantly higher than that of MHC I in the corresponding tissues at most time points (P<0.05). These results demonstrated the MHC genes played an important role in response to bacterial infection in M. amblycephala; however, MHC class I and II genes showed different functional activity, which need be further investigated in teleost.

Molecular cloning, genomic structure, polymorphism and expression analysis of major histocompatibility complex class IIA gene of swamp eel Monopterus albus

Major histocompatibility complex (MHC) class II molecules play an important role in the immune response of vertebrates. In this paper, full-length MHC IIA cDNA was isolated from swamp eel (Monopterus albus) by rapid amplification of cDNA ends PCR. The genomic structure, molecular polymorphism, tissue distribution, and immune response of the MHC IIA gene to bacterial challenge were investigated. The full-length cDNA (GenBank accession No.: KC616308) is 1,509 bp in length including an 83 bp-long 5' untranslated region (UTR) and a 709 bp-long 3' UTR, which encoded a 238 amino acids protein. In the 2,339 bp-long MHC IIA genomic DNA, four exons and three introns were identified. Sequence comparison exhibited that the deduced amino acid sequence shared 27.1-66.3% identity with those of other species. Seven alleles were identified from five healthy individuals. Number of alleles per individual diversified from two to five. Five different 5' UTR sequences and two different 3' UTR sequences from one individual may infer the existence of five loci at least. Real-time quantitative PCR demonstrated that swamp eel MHC IIA transcripts were ubiquitously expressed in ten tissues, but the expression level was distinctly different. Significant changes were observed in liver, spleen, kidney and intestine after challenged with pathogenic bacteria Aeromonas hydrophilia.