Identification and characterization of CD40 from humphead snapper (Lutjanus sanguineus)

Extensive involvement of CD40 and CD154 costimulators in multiple T cell-mediated responses in a perciform fish Larimichthys crocea

CD40 and CD154 are well-characterized costimulatory molecules involved in adaptive humoral immunity in humans and other mammals. These two costimulatory molecules were found to be originated from teleost fish during vertebrate evolution. However, the functionality of fish CD40 and CD154 remains to be explored. In this study, we identified the CD40 and CD154 homologs (LcCD40 and LcCD154) from large yellow croaker (Larimichthys crocea), a marine species of the perciform fish family. The LcCD40 and LcCD154 share conserved structural features to their mammalian counterparts, and are widely expressed in immune-relevant tissues and leukocytes at different transcriptional levels. Immunofluorescence staining and FCM analysis showed that LcCD40 and LcCD154 proteins are distributed on MHC-II⁺ APCs and CD4-2⁺ T cells, and are significantly upregulated in response to antigen stimulation. Co-IP assay exhibited strong association between LcCD40 and LcCD154 proteins. Blockade of LcCD154 with anti-LcCD154 antibody (Ab) or recombinant soluble LcCD40-Ig fusion protein remarkably decreased the MHC-II⁺ APC-initiated CD4⁺ T cell response upon Aeromonas hydrophila stimulation, and alloreactive T cell activation as examined by mixed lymphocyte reaction (MLR). These findings highlight the costimulatory role of LcCD40 and LcCD154 in T cell activities in Larimichthys crocea. Thus, the CD40 and CD154 costimulators may extensively participate in the regulation of multiple T cell-mediated immune responses in teleost fish. It is anticipated that this study would provide a cross-species understanding of the evolutionary history of CD40 and CD154 costimulatory signals from fish to mammals.

Cluster of differentiation antigens: essential roles in the identification of teleost fish T lymphocytes

Cluster of differentiation (CD) antigens are cell surface molecules expressed on leukocytes and other cells associated with the immune system. Antibodies that react with CD antigens are known to be one of the most essential tools for identifying leukocyte subpopulations. T lymphocytes, as an important population of leukocytes, play essential roles in the adaptive immune system. Many of the CD antigens expressed on T lymphocytes are used as surface markers for T lymphocyte classification, including CD3, CD4 and CD8 molecules. In this review, we summarize the recent advances in the identification of CD molecules on T lymphocytes in teleosts, with emphasis on the functions of CD markers in the classification of T lymphocyte subsets. We notice that genes encoding CD3, co-receptors CD4 and CD8 have been cloned in several fish species and antibodies have been developed to study protein expression in morphological and functional contexts. T lymphocytes can be divided into CD4⁺ and CD8⁺ cells discriminated by the expression of CD4 and CD8 molecules in teleost, which are functionally similar to mammalian helper T cells (Th) and cytotoxic T cells (Tc), respectively. Further studies are still needed on the particular characteristics of teleost T cell repertoires and adaptive responses, and results will facilitate the health management and development of vaccines for fish.

Structures, evolutionary relationships and expression profiles of the tumour necrosis factor superfamily and their receptors in black rockfish (Sebastes schlegelii)

Members of tumour necrosis factor superfamily (TNFSF) and TNF receptor superfamily (TNFRSF) have crucial roles in many important biological processes such as cell proliferation, cell death, development, survival, immunity, and various diseases. The human TNFSF consists of 19 ligands and 29 receptors. Compared with those in human, fish have most of the TNFSF and receptors that have been found in mammals, while some of the homologues are specific or lost in fish. Especially, no systematic report on the identification of TNFSF ligands and their receptors in S. schlegelii. Therefore, to investigate the characterization and molecular evolution of TNFSF and TNFRSF genes in Sebastes schlegelii, we performed a genome-wide survey and identified 14 TNFSFs and 24 TNFRSFs from S. schlegelii. In S. schlegelii, we found duplication events occurred in TNFSF2, TNFSF6, TNFSF10, TNFSF13, TNFSF14, TNFRSF5, TNFRSF6, TNFRSF6B, TNFRSF10B, TNFRSF16, and TNFRSF19 genes. Among which, the tandem duplications events occurred in TNFSF13 and TNFRSF6, and the whole genome duplications events occurred in the remaining TNFSF and TNFRSF genes. Based on the molecular phylogenetic analysis, 14 TNFSFs were divided into three different clusters and 24 TNFRSFs were classed as three distinct subgroups, respectively. Meanwhile, protein domains and motifs analysis revealed that TNFSF contain homology domain (THD), and TNFRSF have typical cysteine-rich domains (CRDs). Synteny results indicates that the TNFSFs and TNFRSFs neighborhood genes have taken place great changes compared to those in human, fugu and zebrafish. Meanwhile, qRT-PCR results demonstrated that most TNFSFs and TNFSRSFs were significantly differentially expressed in gill, skin and intestine after E. tarda infection with time-dependent manners. In addition, protein-protein interaction network (PPI) analysis indicated that the most related genes connecting to TNFSF and TNFRSFs were TNFSF ligands and receptors. In summary, this study provided a new understanding for characterization and evolution of the TNFSF genes and their receptors in S. schlegelii.

Comparative Transcriptome Analysis of Spleen Reveals Potential Regulation of Genes and Immune Pathways Following Administration of Aeromonas salmonicida subsp. masoucida Vaccine in Atlantic Salmon (Salmo salar)

Aeromonas salmonicida is a global fish pathogen. Aeromonas salmonicida subsp. masoucida (ASM) is classified as atypical A. salmonicida and caused huge losses to salmonid industry in China. Hence, it is of great significance to develop ASM vaccine and explore its protection mechanism in salmonids. In this regard, we conducted RNA-seq analysis with spleen tissue of Atlantic salmon after ASM vaccination to reveal genes, their expression patterns, and pathways involved in immune protections. In our results, a total of 441.63 million clean reads were obtained, and 389.37 million reads were mapped onto the Atlantic salmon reference genome. In addition, 1125, 2126, 1098, 820, and 1351 genes were significantly up-regulated, and 747, 2626, 818, 254, and 908 genes were significantly down-regulated post-ASM vaccination at 12 h, 24 h, 1 month, 2 months, and 3 months, respectively. Subsequent pathway analysis revealed that many differentially expressed genes (DEGs) following ASM vaccination were involved in cytokine-cytokine receptor interaction (TNFRSF11b, IL-17RA, CCR9, and CXCL11), HTLV-I infection (MR1 and HTLV-1), MAPK signaling pathway (MAPK, IL8, and TNF-α-1), PI3K-Akt signaling pathway (PIK3R3, THBS4, and COL2A1), and TNF signaling pathway (PTGS2, TNFRSF21-l, and CXCL10). Finally, the results of qRT-PCR showed a significant correlation with RNA-seq results, suggesting the reliability of RNA-seq for gene expression analysis. This study provided insights into regulation of gene expression and their involved pathways in Atlantic salmon spleen in responses to vaccine, and set the foundation for further study on the vaccine protective mechanism in Atlantic salmon as well as other teleost species.

CD40 induces an antimicrobial response against the intracellular pathogen Streptococcus agalactiae in Nile tilapia, Oreochromis niloticus

Streptococcus agalactiae is a Gram-positive facultative intracellular bacterium that leads to severe economic loss of tilapia worldwide. Previous studies demonstrated that CD40 contributes to host protection against intracellular injection. In this study, CD40 was characterized from Nile tilapia (Oreochromis niloticus), named OnCD40. Sequence analysis showed that open reading frame of OnCD40 was 933 bp, containing a single peptide, a transmembrane domain and four cysteine-rich domains. The qRT-PCR revealed that OnCD40 was expressed in all examined tissues with the most abundant ones in spleen and thymus. After S. agalactiae stimulation, the expression of OnCD40 was significantly induced in most of the detected organs. Moreover, OnCD40-overexpressing fish elicited significant protection against subsequent S. agalactiae challenge; approximately 10000-fold fewer bacteria were detected in spleen of OnCD40-overexpressing fish in comparison with control fish. Thus, CD40 had protecting function in Nile tilapia against intracellular pathogens.

The impact of salinity and dissolved oxygen regimes on transcriptomic immune responses to oil in early life stage Fundulus grandis

Understanding the effects of oil exposure on early life stage fish species is critical to fully assessing the environmental impacts of oil spills. Oil released from the 2010 Deepwater Horizon spill reached habitats where estuarine fish routinely spawn. In addition, estuaries are highly dynamic environments, therefore, fish in these areas are routinely exposed to varying salinity and dissolved oxygen (DO) levels, each of which are known to modulate transcriptional responses. Fish exposed to oil often display altered immune competence, and several studies have shown that Deepwater Horizon oil in particular causes modulation of various immune functions. However, few studies have directly examined how environmental parameters may affect oil-induced immunomodulation, particularly in early life stage fishes when the immune system is still developing. To this end, we examined transcriptional patterns of immune genes and pathways in Fundulus grandis larvae to various oil (0, 15 μg/L), salinity (3, 30 ppt), and DO (2.5, 6 mg/L) regimes in a fully factorial design. Our results suggest that immune pathways are generally activated in all treatment groups with the exception of the Low Salinity/No Oil/Hypoxia treatment where immune pathways are largely suppressed, and the High Salinity/No Oil/Hypoxia treatment where pathways are unchanged. The High Salinity/Oil/Hypoxia treatment had the largest number of enriched immune pathways (44 as defined by IPA and 43 as defined by ConsensusPathDB), indicating that oil under certain environmental conditions has the potential to further modulate immune-related genes, pathways, and responses in fish.

NF-κB signaling induces inductive expression of the downstream molecules and IgD gene in the freshwater carp, Catla catla

Toll-like receptors (TLRs) in innate immune system act as primary sensors in detecting the microbial components and activate their signaling cascades to induce NF-κB (nuclear factor NF-κB) towards the augmentation of immunoglobulin (Ig) synthesis. To gain insights into the efficacy of NF-κB pathway in immunoglobulin D (IgD) synthesis in the Indian Major Carp Catla catla, cloning and sequencing of TLR-signaling downstream molecules [TRAF3 (TNF receptor-associated factor 3), NEMO (nuclear factor-kappa B essential modulator), NF-κB and BAFF (B cell activating factor)] were performed by infecting the fish with pathogens. mRNA expression analysis of the downstream molecules and IgD showed significant up-regulation of these genes in kidney (P ≤ 0.001) as compared to spleen (P ≤ 0.05). To ascertain the role of NF-κB pathway in IgD synthesis, the primary cell culture of kidney and spleen in monolayer cell suspension was treated with NF-κB inhibitor (BAY 11-7082) and down-regulation of BAFF, NEMO, NF-κB, and IgD gene was observed. These results highlight the importance of NF-κB signaling pathway in augmenting the IgD gene expression in the freshwater carp, Catla catla.

Comparative transcriptomic analysis reveals the gene expression profiles in the liver and spleen of Japanese pufferfish (Takifugu rubripes) in response to Vibrio harveyi infection

Japanese pufferfish (Takifugu rubripes) is one of the main marine aquatic fish species cultured in Asia due to its high nutritional value. In recent years, disease caused by Vibrio harveyi infections have led to serious mortality in Japanese pufferfish industry. To understand the complex molecular mechanisms between V. harveyi and Japanese pufferfish, we performed a transcriptome analysis of liver and spleen samples from Japanese pufferfish at 1 and 2 day post-infection. Between-group comparisons revealed 922 genes that were significantly differentially expressed. The altered genes emphasized the function in several immune related pathways including MAPK signaling pathway, JAK-STAT signaling pathway, toll-like receptor signaling pathway, cytokine-cytokine receptor interaction and lysosomal pathway. The data generated in this study provided insight into the responses of Japanese pufferfish against V. harveyi at the transcriptome level, promoting our comprehensive understanding of immune responses for aquatic animal against V. harveyi.

Characterization of CD40+ leukocytes in flounder (Paralichthys olivaceus) and its response after Hirame novirhabdovirus infection and immunization

CD40 is a crucial signal mediating factor in T-dependent B cell responses and involved in many aspects of cellular and humoral immunity. In this paper, recombinant protein of CD40 in flounder (Paralichthys olivaceus) and its antibodies (Abs) were produced, native CD40 molecules in flounder tissues were identified, then the CD40⁺ leukocytes in T/B lymphocytes were characterized, and the variations of CD40⁺ leukocytes in flounder after Hirame novirhabdovirus (HIRRV) infection and immunization were investigated, respectively. The results showed that the Abs could specifically recognize native flounder CD40 molecule at 32 kDa. The proportions of CD40⁺ leukocytes were varied by flounder tissues. CD40⁺/IgM⁺ B lymphocytes, CD40⁺/CD4-1⁺ T lymphocytes, CD40⁺/CD4-2⁺ T lymphocytes and CD40⁺/CD8⁺ T lymphocytes in peripheral blood leukocytes (PBLs) were 1.18 ± 0.27%, 0.69 ± 0.17%, 0.75 ± 0.14% and 0.25 ± 0.14%; were 2.80 ± 0.32%, 0.71 ± 0.19%, 0.88 ± 0.23% and 0.33 ± 0.17% in spleen; 4.11 ± 0.47%, 0.92 ± 0.18%, 1.09 ± 0.17% and 0.9 ± 0.17% in head kidney; 1.92 ± 0.39%, 1.02 ± 0.23%, 1.33 ± 0.38% and 0.67 ± 0.24% in intestine; 1.24 ± 0.36%, 1.21 ± 0.24%, 1.70 ± 0.3% and 0.97 ± 0.21% in gill, respectively. The percentages of CD40⁺ leukocytes in PBLs were significantly increased in both HIRRV infection and immunization groups, and reached their peak levels at 3rd day with 5.70 ± 0.16% and 6.40 ± 0.13%, respectively. Concluded with our previous study, these data first reported that CD40 molecules were expressed on both B and T lymphocytes in teleost, and had a coordination with T and B lymphocytes in immune responses.