Conserved Role of mTORC1 Signaling in B Cell Immunity in Teleost Fish.

Mammalian studies have demonstrated that B cell immune responses are regulated by mechanistic target of rapamycin complex 1 (mTORC1) signaling. Teleost fish represent the oldest living bony vertebrates that contain bona fide B cells. So far, whether the regulatory mechanism of mTORC1 signaling in B cells occurred in teleost fish is still unknown. In this study, we developed a fish model by using rapamycin (RAPA) treatment to inhibit mTORC1 signaling and demonstrated the role of mTORC1 signaling in teleost B cells. In support, we found inhibition of mTORC1 signaling by RAPA decreased the phagocytic capacity, proliferation, and Ig production of B cells. Critically, Flavobacterium columnare induced specific IgM binding in serum, and these titers were significantly inhibited by RAPA treatment, thus decreasing Ab-mediated agglutination of F. columnare and significantly increasing the susceptibility of fish upon F. columnare reinfection. Collectively, our findings elucidated that the mTORC1 pathway is evolutionarily conserved in regulating B cell responses, thus providing a new point for understanding the B cells functions in teleost fish.

Expression analysis of taste receptor genes (T1R1, T1R3, and T2R4) in response to bacterial, viral and parasitic infection in rainbow trout, Oncorhynchus mykiss.

Emerging evidence suggests that bitter and sweet Taste receptors (TRs) in the airway are important sentinels of innate immunity. TRs are G protein-coupled receptors that trigger downstream signaling cascades in response to activation of specific ligands. Among them, the T1R family consists of three genes: T1R1, T1R2, and T1R3, which function as heterodimers for sweet tastants and umami tastants. While the other TRs family components T2Rs function as bitter tastants. To understand the relationship between TRs and mucosal immunity in teleost, here, we firstly identified and analyzed the molecular characteristics of three TRs (T1R1, T1R3, and T2R4) in rainbow trout (Oncorhynchus mykiss). Secondly, by quantitative real-time PCR (qPCR), we detected the mRNA expression levels of T1R1, T1R3 and T2R4 and found that the three genes could be tested in all detected tissues (pharynx, buccal cavity, tongue, nose, gill, eye, gut, fin, skin) and the expression levels of T1R3 and T2R4 were higher in buccal mucosa (BM) and pharyngeal mucosa (PM) compare to other tissues. It may suggest that T1R3 and T2R4 play important roles in BM and PM. Then, to analyses the changes of expression levels of the three genes in rainbow trout infected with pathogens, we established three infection models Flavobacterium columnare (F. cloumnare), infectious hematopoietic necrosis virus (IHNV) and Ichthyophthirius multifiliis (Ich). Subsequently, by qPCR, we detected the expression profiles of TRs in the gustatory tissues (BM, PM and skin) of rainbow trout after infection with F. cloumnare, IHNV, and Ich, respectively. We found that under three different infection models, the expression of the T1R1, T1R3 and T2R4 showed their own changes in mRNA levels. And the expression levels of the T1R1, T1R3 and T2R4 changed significantly at different time points in response to three infection models, respectively, suggesting that TRs may be associated with mucosal immunity.

Gut mucosal immune responses and protective efficacy of oral yeast Cyprinid herpesvirus 2 (CyHV-2) vaccine in Carassius auratus gibelio.

Cyprinid herpesvirus 2 (CyHV-2) causes herpesviral hematopoietic necrosis (HVHN) disease outbreaks in farmed Cyprinid fish, which leads to serious economic losses worldwide. Although oral vaccination is considered the most suitable strategy for preventing infectious diseases in farmed fish, so far there is no commercial oral vaccine available for controlling HVNN in gibel carp (C. auratus gibelio). In the present study, we developed for the first time an oral vaccine against CyHV-2 by using yeast cell surface display technology and then investigated the effect of this vaccine in gibel carp. Furthermore, the protective efficacy was evaluated by comparing the immune response of a single vaccination with that of a booster vaccination (booster-vaccinated once 2 weeks after the initial vaccination). Critically, the activities of immune-related enzymes and genes expression in vaccine group, especially in the booster vaccine group, were higher than those in the control group. Moreover, strong innate and adaptive immune responses could be elicited in both mucosal and systemic tissues after receipt of the oral yeast vaccine. To further understand the protective efficacy of this vaccine in gibel carp, we successfully developed the challenge model with CyHV-2. Our results showed the relative percent survival was 66.7% in the booster vaccine group, indicating this oral yeast vaccine is a promising vaccine for controlling CyHV-2 disease in gibel carp aquaculture.

Expression analysis of Igs and mucosal immune responses upon SVCV infection in common carp (Cyprinus carpio L.).

The immunoglobulin (Ig) is a crucial component of adaptive immune system in vertebrates including teleost fish. Here complete cDNA sequence of IgD heavy chain gene from common carp (Cyprinus carpio) was cloned and analyzed. The full-length cDNA of IgD heavy chain gene contained an open reading frame (ORF) of 2460 bp encoding 813 amino acids. According to amino acids sequence, multiple alignment and phylogenetic analysis showed that carp Igs are closely related to those of Cyprinidae fish. Transcriptional expression of IgD as well as IgM, IgZ1 and IgZ2 showed similar expression patterns in different organs, this is, high expression level in systemic immune tissues (ie, head kidney, heart and spleen) and low expression in mucosal tissues (ie, gill, skin and gut). Following viral infection with spring viraemia of carp virus (SVCV), obvious pathological changes in skin, gill and gut mucosa and up-regulated expression of antiviral related genes in skin, gill, gut and spleen were observed, indicating that SVCV successfully infected common carp and activated the systemic and mucosal immune system. Interestingly, IgM showed a significant up-regulation only in systemic tissue (spleen), but not in mucosal tissues (gut, gills and skin), while increased expression of IgZ1 and IgZ2 was found in gut. In contrast, the expression of IgD increased significantly in spleen, gills and skin. These strongly suggest that fish Ig isotypes play different roles in mucosal and systemic immunity during viral infection. Common carp (Cyprinus carpio); Igs; Spring viraemia of carp virus (SVCV).