Expression responses of the complement components in zebrafish organs after stimulation with poly I:C, mimicry of viral infection

Defensive roles of the complement system in fish are largely unknown, although expressions of several complement components have been examined in some teleost species upon bacterial and parasitic infections. To infer possible anti-virus defensive roles of the complement system in teleost, zebrafish were simulated by intraperitoneal injection of poly I: C, a double strand RNA analogue, to mimic viral infection, and expression of 24 complement components and their subunits in the gill, brain, kidney, gut, hepatopancreas, gonad, heart, spleen, and skin were analyzed by reverse-transcription PCR. In normal (unstimulated) fish, the hepatopancreas showed highest expression of most genes tested, and considerable extra hepatic expression was also observed for many complement components. Upon stimulation, the hepatopancreas showed decreased expression of CD11/CD18, B/C2-A3, MASP3, and properdin, while marked up-regulation of several complement component genes was observed in the gill, suggesting an important but unknown role of the gill in host defense against viral infection.