Two distinct interferon-γ genes in Tetraodon nigroviridis: Functional analysis during Vibrio parahaemolyticus infection

Interferon gamma (IFNγ) is a Th1 cytokine that plays a very important role in almost all phases of immune and inflammatory responses. In this study, we explored the functions of IFNγ1 and IFNγ2 of Tetraodon nigroviridis. Treating T. nigroviridis spleen and head kidney cells in vitro with recombinant T. nigroviridis IFNγ1 protein (rTn IFNγ1) or recombinant T. nigroviridis IFNγ2 protein (rTn IFNγ2) enhanced their nitric oxide responses. Both rTn IFNγ1 and rTn IFNγ2 also induced the expression of interferon-stimulated gene 15 (ISG15), a common anti-viral gene, although the expression of the interferon-inducible Mx gene was markedly inhibited by rTn IFNγ1 and was induced by rTn IFNγ2. The in vivo effects of rTn IFNγ1 and rTn IFNγ2 on Vibrio parahaemolyticus (V. parahaemolyticus) infection were assessed by intraperitoneally injecting rTn IFNγ1 or rTn IFNγ2 (100 ng) and V. parahaemolyticus (8 × 1010 CFU/mL) into T. nigroviridis. A comparison of the group treated only with V. parahaemolyticus and those also treated with rTn IFNγ1 or rTn IFNγ2 showed that neither of these IFNγs protected T. nigroviridis from V. parahaemolyticus infection. However, rTn IFNγ1 more rapidly and robustly promoted inflammatory responses compared with rTn IFNγ2, whereas rTn IFNγ2 was involved in inducing the host to develop a more effective response earlier during the later stage of a V. parahaemolyticus infection. Moreover, microRNA-29b (miR-29b) expression is inversely correlated with IFNγ2 expression in T. nigroviridis.