Fish TRAF2 promotes innate immune response to RGNNV infection

Slc43a2+ T cell metastasis from spleen to brain in RGNNV infected teleost

The origin of T cells in the teleost's brain is unclear. While viewing the central nervous system (CNS) as immune privileged has been widely accepted, previous studies suggest that T cells residing in the thymus but not in the spleen of the teleost play an essential role in communicating with the peripheral organs. Here, we identified nine T cell subpopulations in the thymus and spleen of orange-spotted grouper (Epinephelus coioices) through single-cell RNA-sequencing analysis. After viral CNS infection with red-spotted grouper nervous necrosis virus (RGNNV), the number of slc43a2+ T cells synchronously increased in the spleen and brain. During the infection tests in asplenic zebrafish (tlx1▲ zebrafish model), no increase in the number of slc43a2+ T cells was observed in the brain. Single-cell transcriptomic analysis indicated that slc43a2+ T cells mature and functionally differentiate within the spleen and then migrate into the brain to trigger an immune response. This study suggests a novel route for T cell migration from the spleen to the brain during viral infection in fish.

Identification of the NOD-like receptor family of golden pompano and expression in response to bacterial and parasitic exposure reveal its key role in innate immunity

This study presents a genome-wide identification of NOD-like receptors (NLRs) in the golden pompano, key to its innate immunity. We identified 30 ToNLRs, analyzing their chromosomal positions, characteristics, evolutionary relationships, evidence of positive selection, and synteny with the yellowtail kingfish. Our findings categorize these NLRs into three main subgroups: NLRA, NLRC, and the distinct ToNLRX1. Post-exposure to Streptococcus agalactiae, most ToNLRs increased expression in the spleen, whereas NLRC3like13, NLRC3like16, and NLRC3like19 so in the kidneys. Upon Cryptocaryon irritans exposure, we categorized our groups based on the site of infection into the control group (BFS), the trophont-attached skin (TAS), and the nearby region skin (NRS). ToAPAF1 and ToNOD1 expressions rose in the NRS, in contrast to decreased expressions of ToNLRC5, ToNWD1 and ToCIITA. Other ToNLRs showed variable expressions in the TAS. Overall, this research lays the groundwork for further exploration of innate immunity in the golden pompano.

Transcriptomic profiling reveals the immune response mechanism of the Thamnaconus modestus induced by the poly (I:C) and LPS

Aquatic animals immune response to pathogenic is a hotspot and related to high-quality development of aquaculture industry and the conservation of fisheries resources. Thamnaconus modestus is an important commercial and economical species which is suffering from various pathogens but by now lack relevant research about revealing the immune response mechanism to the pathogens invasion. In the study, the polyriboinosinic polyribocytidylic acid [poly (I:C)] and Lipopolysaccharides (LPS), respective mimics of viral and bacterial infections, were used to demonstrate the immune response of the species via transcriptome analysis. The results showed that T. modestus had sensitive responses to the viral analog infection at 6 h and 48 h, and at 6 h, the first five major functional genes were NFKBIA, IL1B, JUN, IGH, FOS, and at 48 h, the genes were NFKBIA, IL1B, JUN, IGH, FOS. The genes IL1B, IRF3, PTGS2, THBS1 could helping the fish to fight against the bacterial infection in both the times. Similarly for the bacterial infection, the species had a sensitive response at 6 h, and the first five major functional genes were NFKBIA, JUN, FOS, L1B, GRIN2C. Our study provided an insight about the immune response mechanism of this species and demonstrated that if need for treatment of the virus and bacteria by the biotechnology, the artificial interferential time would be suggested before 6 h since the pathological features occur and the genes NFKBIA, JUN, IL1B, FOS, TRAF2, IL8, SOCS3, PTGS2 should be payed more attention.

Grouper Rab1 inhibits nodovirus infection by affecting virus entry and host immune response

Rab1, a GTPase, is present in all eukaryotes, and is mainly involved in vesicle trafficking between the endoplasmic reticulum and Golgi, thereby regulating many cellular activities and pathogenic infections. However, little is known of how Rab1 functions in fish during virus infection. Groupers (Epinephelus spp.) are high in economic value and widely cultivated in China and Southeast Asia, although they often suffer from diseases. Red-spotted grouper nervous necrosis virus (RGNNV), a highly pathogenic RNA virus, is a major pathogen in cultured groupers, and causes huge economic losses. A series of host cellular proteins involved in RGNNV infection was identified. However, the impact of Rab1 on RGNNV infection has not yet been reported. In this study, a novel Rab1 homolog (EcRab1) from Epinephelus coioides was cloned, and its roles during virus infection and host immune responses were investigated. EcRab1 encoded a 202 amino acid polypeptide, showing 98% and 78% identity to Epinephelus lanceolatus and Homo sapiens, respectively. After challenge with RGNNV or poly(I:C), the transcription of EcRab1 was altered both in vitro and in vivo, implying that EcRab1 was involved in virus infection. Subcellular localization showed that EcRab1 was displayed as punctate structures in the cytoplasm, which was affected by EcRab1 mutants. The dominant negative (DN) EcRab1, enabling EcRab1 to remain in the GDP-binding state, caused EcRab1 to be diffusely distributed in the cytoplasm. Constitutively active (CA) EcRab1, enabling EcRab1 to remain in the GTP-binding state, induced larger cluster structures of EcRab1. During the late stage of RGNNV infection, some EcRab1 co-localized with RGNNV, and the size of EcRab1 clusters was enlarged. Importantly, overexpression of EcRab1 significantly inhibited RGNNV infection, and knockdown of EcRab1 promoted RGNNV infection. Furthermore, EcRab1 inhibited the entry of RGNNV to host cells. Compared with EcRab1, overexpression of DN EcRab1 or CA EcRab1 also promoted RGNNV infection, suggesting that EcRab1 regulated RGNNV infection, depending on the cycles of GTP- and GDP-binding states. In addition, EcRab1 positively regulated interferon (IFN) immune and inflammatory responses. Taken together, these results suggest that EcRab1 affects RGNNV infection, possibly by regulating host immunity. Our study furthers the understanding of Rab1 function during virus infection, thus helping to design new antiviral strategies.

Engagement of gcFKBP5/TRAF2 by spring viremia of carp virus to promote host cell apoptosis for supporting viral replication in grass carp

Spring viremia of carp virus (SVCV) causes severe morbidity and mortality in grass carp (Ctenopharyngodon idellus) in Europe, America and several Asian countries. We found that FKBP5 (FK506-binding protein 5) is an SVCV infection response factor; however, its role in the innate immune mechanism caused by SVCV infection remains unknown. This study cloned gcFKBP5 (grass carp FKBP5) and made its mimic protein structure for function discussion. We found that gcFKBP5 expression in the primary innate immune organs of grass carp, including intestine, liver and spleen, was highly upregulated by SVCV in 24 h, with a similar result in fish cells by poly(I:C) treatment. gcFKBP overexpression aggravates viral damage to cells and increases viral replication. Furthermore, SVCV engages gcFKBP5 interacting with TRAF2 (tumour necrosis factor receptor-associated factor 2) to promote host cell apoptosis for supporting viral replication. The enhanced viral replication seems not to be due to the repression of IFN and other antiviral factors as expected. For the first time, these data show the pivotal role of gcFKBP5 in the innate immune response of grass carp to SVCV infection.

Single-cell RNA-seq landscape midbrain cell responses to red spotted grouper nervous necrosis virus infection

Viral nervous necrosis (VNN) is an acute and serious fish disease caused by nervous necrosis virus (NNV) which has been reported massive mortality in more than fifty teleost species worldwide. VNN causes damage of necrosis and vacuolation to central nervous system (CNS) cells in fish. It is difficult to identify the specific type of cell targeted by NNV, and to decipher the host immune response because of the functional diversity and highly complex anatomical and cellular composition of the CNS. In this study, we found that the red spotted grouper NNV (RGNNV) mainly attacked the midbrain of orange-spotted grouper (Epinephelus coioides). We conducted single-cell RNA-seq analysis of the midbrain of healthy and RGNNV-infected fish and identified 35 transcriptionally distinct cell subtypes, including 28 neuronal and 7 non-neuronal cell types. An evaluation of the subpopulations of immune cells revealed that macrophages were enriched in RGNNV-infected fish, and the transcriptional profiles of macrophages indicated an acute cytokine and inflammatory response. Unsupervised pseudotime analysis of immune cells showed that microglia transformed into M1-type activated macrophages to produce cytokines to reduce the damage to nerve tissue caused by the virus. We also found that RGNNV targeted neuronal cell types was GLU1 and GLU3, and we found that the key genes and pathways by which causes cell cytoplasmic vacuoles and autophagy significant enrichment, this may be the major route viruses cause cell death. These data provided a comprehensive transcriptional perspective of the grouper midbrain and the basis for further research on how viruses infect the teleost CNS.

Grouper TRAF4, a Novel, CP-Interacting Protein That Promotes Red-Spotted Grouper Nervous Necrosis Virus Replication

Tumor necrosis factor receptor-associated factors (TRAFs) play important roles in the biological processes of immune regulation, the inflammatory response, and apoptosis. TRAF4 belongs to the TRAF family and plays a major role in many biological processes. Compared with other TRAF proteins, the functions of TRAF4 in teleosts have been largely unknown. In the present study, the TRAF4 homologue (EcTRAF4) of the orange-spotted grouper was characterized. EcTRAF4 consisted of 1413 bp encoding a 471-amino-acid protein, and the predicted molecular mass was 54.27 kDa. EcTRAF4 shares 99.79% of its identity with TRAF4 of the giant grouper (E. lanceolatus). EcTRAF4 transcripts were ubiquitously and differentially expressed in all the examined tissues. EcTRAF4 expression in GS cells was significantly upregulated after stimulation with red-spotted grouper nervous necrosis virus (RGNNV). EcTRAF4 protein was distributed in the cytoplasm of GS cells. Overexpressed EcTRAF4 promoted RGNNV replication during viral infection in vitro. Yeast two-hybrid and coimmunoprecipitation assays showed that EcTRAF4 interacted with the coat protein (CP) of RGNNV. EcTRAF4 inhibited the activation of IFN3, IFN-stimulated response element (ISRE), and nuclear factor-κB (NF-κB). Overexpressed EcTRAF4 also reduced the expression of interferon (IFN)-related molecules and pro-inflammatory factors. Together, these results demonstrate that EcTRAF4 plays crucial roles in RGNNV infection.