Comparison of Macrophage Antimicrobial Responses Induced by Type II Interferons of the Goldfish (Carassius auratus L.)

Unlike mammals, bony fish have two type II interferons, IFN gamma and IFN gamma rel, whose pro-inflammatory functions have not been fully characterized. To elucidate the distinct roles of these type II interferons of bony fish, we examined the effects of recombinant goldfish (rg) IFN gamma and IFN gamma rel on the macrophage antimicrobial responses, immune gene expression, and their signaling pathways. Our findings indicate that rgIFN gamma and rgIFN gamma rel possess unique capacities to mediate each of the above processes. Q-PCR analysis revealed similar expression of both cytokines in tissues and immune cell populations of the goldfish, although IFN gamma mRNA levels were generally higher in most tissues and cell types. Whereas rgIFN gamma had long-lasting effects on the priming of goldfish monocyte ROI production, the rgIFN gamma rel had relatively short-lived ROI priming potential and eventually down-regulated the priming of ROI production induced by rgIFN gamma or rgTNF alpha 2. Whereas rgIFN gamma induced relatively modest phagocytic and nitric oxide responses of goldfish macrophages, rgIFN gamma rel induced significantly higher phagocytosis, iNOSA and iNOSB gene expression and nitric oxide production compared with rgIFN gamma. The rgIFN gamma and rgIFN gamma rel induced different gene expression profiles in goldfish monocytes. These differences included significantly higher induction of TNF alpha 2, CXCL8, ceruloplasmin, and interferon regulatory factor (IRFs) expression after activation of monocytes with rgIFN gamma rel. The rgIFN gamma rel was more abundant in whole cell lysates compared with rgIFN gamma. Both cytokines induced the phosphorylation of Stat1, while the nuclear localization of Stat1 was only observed following treatment of monocytes with rgIFN gamma. Our findings suggest the presence of functional segregation of the induction of macrophage antimicrobial functions by type II interferons of bony fish.