Class II, major histocompatibility complex, transactivator (CIITA) in channel catfish: identification and expression patterns responding to different pathogens

Impact of VHSV on CIITA-mediated MHCII expression and antigen presentation in largemouth bass

Viral hemorrhagic septicemia virus (VHSV) infection poses a significant threat to fish immunity by evading antigen presentation. Our previous study indicated that VHSV inhibited the transcriptional activation of MHC class II (MHCII) to impair antigen presentation in vitro, but the underlying mechanisms remain unclear. Here, we cloned and characterized the class II major histocompatibility complex transactivator (CIITA) in largemouth bass (Micropterus salmoides), a key regulator of MHCII expression, demonstrating that it activates MHCII transcription and possesses antiviral properties against VHSV. Following VHSV infection, CIITA and its downstream target MHCII were significantly downregulated in vivo. Further analysis revealed that the VHSV N protein degrades CIITA, primarily via its H3 and FCH domains, thereby impairing MHCII expression and antigen presentation. This study uncovers a critical mechanism through which VHSV inhibits adaptive immunity in fish and provides a theoretical basis for developing live-attenuated VHSV vaccines.

Progresses on three pattern recognition receptor families (TLRs, RLRs and NLRs) in teleost

Pattern recognition receptors (PRRs) are a class of immune sensors that play crucial roles in detecting and responding to the conserved patterns of microorganisms. To date, many PRRs, such as TLRs, RLRs and NLRs, as well as their downstream molecules have been identified and characterized in teleost, while their ligands and immunoregulatory mechanisms remain largely unknown. In the present review, we described and discussed the main members of TLR/RLR/NLR families, including their expression profiles, signaling transductions and functions in teleost. And some splicing isoforms from TLR/RLR/NLR families were also addressed, which play synergistic and/or antagonistic roles in response to pathogen infections in teleost. TLRs sense different pathogens by forming homodimer and/or heterodimer. Beyond, functions of TLRs can also be affected by migrating. And some endolysosomal TLRs undergo proteolytic cleavage and in a pH-dependent mechanism to attain a mature functional form that mediate ligand recognition and downstream signaling. Until now, more than 80 members in TLR/RLR/NLR families have been identified in teleost, while only TLR5, TLR9, TLR19, TLR21, TLR22, MDA5, LGP2, NOD1 and NOD2 have direct evidence of ligand recognition in teleost. Meanwhile, new ligands as well as signaling pathways do occur during evolution of teleost. This review summarizes progresses on the TLRs/RLRs/NLRs in teleost. We attempt to insight into the ligands recognition and signaling transmission of TLRs/RLRs/NLRs in teleost.

Molecular cloning and immune characterization of CIITA in artificially challenged Chinese tongue sole (Cynoglossus semilaevis) with Vibrio harveyi

In mammals, Class II, major histocompatibility complex (MHC II) transactivator (CIITA) recognizes microbial pathogens and triggers immune responses. In Chinese tongue sole Cynoglossus semilaevis, Cs-CIITA was prevalently expressed in various tissues. Cs-CIITA, Cs-MHC IIA and Cs-MHC IIB were expressed significantly higher in skin in susceptible families infected with Vibrio harveyi, while higher expression of Cs-CIITA and Cs-MHC IIB was examined in liver in resistant families. In addition, the three genes were up-regulated in gill, skin, intestine, liver, spleen and kidney at 48 h or 72 h after V. harveyi infection. Furthermore, the three genes were co-expressed in the epithelial mucous cells of gill, skin, and intestine. Knockdown of Cs-CIITA regulates the expression of other inflammation-related genes, including CD40, IL-1β, IL-8, RelB, NFκB, and Myd88. These results suggest that CIITA functions in the inflammatory responses of C. semilaevis against V. harveyi, via MHC II transcriptional regulation.

Host-microbiota interactions and responses to grass carp reovirus infection in Ctenopharyngodon idellus

Gut microbiota could facilitate host to defense diseases, but fish-microbiota interactions during viral infection and the underlying mechanism are poorly understood. We examined interactions and responses of gut microbiota to grass carp reovirus (GCRV) infection in Ctenopharyngodon idellus, which is the most important aquaculture fish worldwide. We found that GCRV infection group with serious haemorrhagic symptoms (G7s) showed considerably different gut microbiota, especially with an abnormally high abundance of gram-negative anaerobic Cetobacterium somerae. It also showed the lowest (p < 0.05) alpha-diversity but with much higher ecological process of homogenizing dispersal (28.8%), confirming a dysbiosis of the gut microbiota after viral infection. Interestingly, signaling pathways of NOD-like receptors (NLRs), toll-like receptors (TLRs), and lipopolysaccharide (LPS) stimulation genes were significantly (q-value < 0.01) enriched in G7s, which also significantly (p < 0.01) correlated with the core gut microbial genera of Cetobacterium and Acinetobacter. The results suggested that an expansion of C. somerae initiated by GCRV could aggravate host inflammatory reactions through the LPS-related NLRs and TLRs pathways. This study advances our understanding of the interplay between fish immunity and gut microbiota challenged by viruses; it also sheds new insights for ecological defense of fish diseases with the help of gut microbiota.

Interferon Regulatory Factors 1 and 2 Play Different Roles in MHC II Expression Mediated by CIITA in Grass Carp, Ctenopharyngodon idella

Expression of major histocompatibility complex class II (MHC II) molecules, which determines both the immune repertoire during development and subsequent triggering of immune responses, is always under the control of a unique (MHC class II) transactivator, CIITA. The IFN-γ-inducible MHC II expression has been extensively and thoroughly studied in humans, but not in bony fish. In this study, the characterization of CIITA was identified and its functional domains were analyzed in grass carp. The absence of GAS and E-box in the promoter region of grass carp CIITA, might imply that the cooperative interaction between STAT1 and USF1 to active the CIITA expression, found in mammals, is not present in bony fish. After the transfection of IFN-γ or IFN-γ rel, only IFN-γ could induce MHC II expression mediated by CIITA. Moreover, interferon regulatory factor (IRF) 2, which cooperates with IRF1 to active the CIITA promoter IV expression in mammals, played an antagonistic role to IRF1 in the activation of grass carp CIITA. These data suggested that grass carp, compared with mammals, has both conservative and unique mechanisms in the regulation of MHC II expression.

Single nucleotide polymorphisms in candidate genes are significantly associated with resistance to Haemonchus contortus infection in goats

BACKGROUND

Haemonchosis is a major economic problem in goat production in humid, tropical and subtropical regions. The disease is caused by an abomasal nematode, Haemonchus contortus, which is highly pathogenic in small ruminants. The aim of this study was to identifying single-nucleotide polymorphisms (SNP) that were associated with fecal egg counts (FEC) and could be used as markers to identify resistance to H. contortus in goats.

RESULTS

Ten novel variants in the CIITA, ATP2A3, HSPA8, STAT5B, ESYT1, and SERPING1 genes were associated with FEC in goats with a nominal significance level of P < 0.05. Two missense mutation in the exon region of the caprine CIITA gene resulted in replacement of arginine with cysteine at position 9473550 (R9473550C) and aspartic acid with glutamic acid at position 9473870 (D9473870E). Chinese goat breeds had significantly higher FEC than Bangladeshi goat breeds within their respective genotypes. Polymorphism information content (PIC), effective allele number (Ne), and heterozygosity (He) were greatest for the STAT5B_197_A > G SNP locus in all goat breeds. Pairwise coefficients of linkage disequilibrium (D´, r 2) revealed complete LD (r 2 = 1) between significant SNP polymorphisms in CIITA and SERPING1 and strong LD (r 2 = 0.93 and 0.98) between polymorphisms in HSPA8 and ATP2A3, respectively. Correlation coefficient (r) between FEC and body weight (BW) was significantly positive (r = 0.56***, P < 0.001) but that between FEC and packed cell volume (PCV) was negatively significant (r = - 0.47**, P < 0.01) in the total population of goats. On the other hand, correlation coefficient (r) between BW and PCV was not significant in total population of goats. Association analysis revealed that haplotypes within ATP2A3, HSPA8, and SERPING1 were significantly associated with FEC. Quantitative real-time PCR revealed that the relative expression of mRNA was higher (P < 0.001) for resistant, compared to susceptible, groups of goats for all candidate genes except CIITA.

CONCLUSIONS

This study identified SNP markers that can potentially be used in marker-assisted selection programs to develop goat breeds that are resistant to H. contortus.

Molecular Cloning, Characterization, and Anti-avian Pathogenic Escherichia coli Innate Immune Response of the Cherry Valley Duck CIITA Gene

Class II major histocompatibility complex (MHC-II) transactivator (CIITA) is a member of the pattern recognition receptor in cytoplasm, which is involved in host innate immune responses. In this study, the full-length cDNA of Cherry Valley duck CIITA (duCIITA) was cloned from the spleen of healthy Cherry Valley ducks for the first time. The CDs of duCIITA have 3648 bp and encode 1215 amino acids. The homology analysis of CIITAs amino acid sequence showed that the duCIITA has the highest identity with the Anas platyrhynchos (94.9%), followed by Gallus gallus and Meleagris gallopavo. Quantitative real-time PCR analysis indicated that duCIITA mRNA has a broad expression level in healthy Cherry Valley duck tissues. It was highly expressed in the lung and cerebellum, and lowly expressed in the rectum and esophagus. After the avian pathogenic Escherichia coli (APEC) O1K1 infection, the ducks exhibited the typical clinical symptoms, and a severe fibrinous exudate in the heart and liver surface was observed. Meanwhile, a significant up-regulation of duCIITA was detected in the infected liver. The inflammatory cytokines IL-1β, IL-6, and IL-8 have a significant up-regulation in the infected liver, spleen and brain. In addition, knockdown of the duCIITA reduces antibacterial activity and inflammatory cytokine production of the duck embryo fibroblast cells. Our research is the first study of the cloning, tissue distribution, and antibacterial immune responses of duCIITA, and these findings imply that duCIITA was an important receptor, which was involved in the early stage of the antibacterial innate immune response to APEC O1K1 infection of Cherry Valley duck.

Alternative Pre-mRNA Splicing in Mammals and Teleost Fish: A Effective Strategy for the Regulation of Immune Responses Against Pathogen Infection

Pre-mRNA splicing is the process by which introns are removed and the protein coding elements assembled into mature mRNAs. Alternative pre-mRNA splicing provides an important source of transcriptome and proteome complexity through selectively joining different coding elements to form mRNAs, which encode proteins with similar or distinct functions. In mammals, previous studies have shown the role of alternative splicing in regulating the function of the immune system, especially in the regulation of T-cell activation and function. As lower vertebrates, teleost fish mainly rely on a large family of pattern recognition receptors (PRRs) to recognize pathogen-associated molecular patterns (PAMPs) from various invading pathogens. In this review, we summarize recent advances in our understanding of alternative splicing of piscine PRRs including peptidoglycan recognition proteins (PGRPs), nucleotide binding and oligomerization domain (NOD)-like receptors (NLRs), retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) and their downstream signaling molecules, compared to splicing in mammals. We also discuss what is known and unknown about the function of splicing isoforms in the innate immune responses against pathogens infection in mammals and teleost fish. Finally, we highlight the consequences of alternative splicing in the innate immune system and give our view of important directions for future studies.

Transcriptome analysis of immune response genes induced by pathogen agonists in the Antarctic bullhead notothen Notothenia coriiceps

Fish are a representative population of lower vertebrates that serve as an essential link to early vertebrate evolution, and this has fueled academic interest in studying ancient vertebrate immune defense mechanisms in teleosts. Notothenia coriiceps, a typical Antarctic notothenioid teleost, has evolved to adapt to the cold and thermally stable Antarctic sea. In this study, we examined adaptive signaling pathways and immune responses to bacterial and viral pathogenic exposure in N. coriiceps. Using RNA sequencing, we investigated transcriptional differences in the liver tissues of N. coriiceps challenged with two pathogen-mimicking agonists, a bacterial ligand (heat-killed Escherichia coli, HKEB) and a viral ligand (polyinosinic:polycytidylic acid, Poly I:C). We found that 567 unique genes were up-regulated two-fold in the HKEB-exposed group, whereas 392 unique genes, including 124 immune-relevant genes, were up-regulated two-fold in the Poly I:C-exposed group. A KEGG pathway analysis of the 124 immune-relevant genes revealed that they exhibited major features of antigen processing and presentation bacterial ligand exposure, but they were down-regulated after viral ligand exposure. A quantitative real time RT-PCR analysis revealed that TNFα and TNF2, major inducers of apoptosis, were highly up-regulated after exposure to the viral ligand but not the bacterial ligand. The results suggest that the bacterial and viral ligands up-regulate inducers of different immune mechanisms in N. coriiceps liver tissue. N. coriiceps has an immune response defense strategy that uses antigen presentation against bacterial infection, but it may use a different defense, such as TNF-mediated apoptosis, against viral infection. The specific immune responses of N. coriiceps may be adaptations to the Antarctic environment and pathogens. These results will help define the characteristics of Antarctic fish and increase our understanding of their immune response mechanisms.

Insights into the antiviral immunity against grass carp (Ctenopharyngodon idella) reovirus (GCRV) in grass carp

Global fish production from aquaculture has rapidly grown over the past decades, and grass carp shares the largest portion. However, hemorrhagic disease caused by grass carp reovirus (GCRV) results in tremendous loss of grass carp (Ctenopharyngodon idella) industry. During the past years, development of molecular biology and cellular biology technologies has promoted significant advances in the understanding of the pathogen and the immune system. Immunoprophylaxis based on stimulation of the immune system of fish has also got some achievements. In this review, authors summarize the recent progresses in basic researches on GCRV; viral nucleic acid sensors, high-mobility group box proteins (HMGBs); pattern recognition receptors (PRRs), Toll-like receptors (TLRs) and retinoic acid inducible gene I- (RIG-I-) like receptors (RLRs); antiviral immune responses induced by PRRs-mediated signaling cascades of type I interferon (IFN-I) and IFN-stimulated genes (ISGs) activation. The present review also notices the potential applications of molecule genetic markers. Additionally, authors discuss the current preventive and therapeutic strategies (vaccines, RNAi, and prevention medicine) and highlight the importance of innate immunity in long term control for grass carp hemorrhagic disease.

Molecular characterization of chicken class II transactivator gene

Class II transactivator (CIITA) is an effective transcriptional factor regulating various genes in the immune system. Since the detection of CIITA in 1993, there has been considerable progress toward understanding its role as an activator of MHC II genes in human and mouse; however, there is little knowledge of this gene in other animals such as chicken. Molecular characterization of the chicken CIITA gene transcript was performed to determine its sequence and expression in different tissues. The CIITA cDNA was first generated through reverse transcriptase-polymerase chain reaction (RT-PCR) from Cobb chicken spleen cell RNA, using oligonucleotide primers based on the predicted cDNA sequence. The effect of the immune system stimulation on the CIITA gene expression in kidney, liver, thymus, and spleen were assessed by semi-quantitative RT-PCR analysis. A partial cDNA sequence (1,688 bp) encoding part of the NACHT domain followed by seven of the transactivator and one of the NLS domains were obtained. Comparison of the deduced amino acid sequence with other CIITAs reveals high level of similarities in amino acid composition, secondary structure and phosphorylation sites. Furthermore, in comparison to the Red Jungle Fowl (RJF) sequence, we found 17 single nucleotide polymorphisms in Cobb broiler chicken, ten of which were reported for the first time. Gene expression analysis indicated that CIITA RNA amounts increased in all the examined tissues following stimulation with Brucella antigen. This investigation may indicate that CIITA molecule has an important role in the chicken immune responses as well as human and other animals.