Response of gene expression to LPS challenge manifests the ontogeny and maturation of the complement system in zebrafish larvae

Information on the ontogeny of complement system might help us better understand the anti-infection mechanism in the early fish life. The ontogenic expression of the representative complement genes and their response to lipopolysaccharides (LPS) challenge in zebrafish larvae are reported here. The expression of C1r/s, C3, C4, C6 and MBL steadily increased before 21 days post-fertilization (dpf) and a decrease was detected thereafter. MASP expression elevated and peaked on 14 dpf and a decline followed. Bf expression fluctuated during the experimental period. Moreover, Bf (involved in alternative pathway, AP) expressed at higher levels than C1r/s (involved in classical pathway, CP), MASP (involved in lectin pathway, LP) and C4 (involved in both CP and LP) in the normal adult fish and larvae, suggesting the more significance of AP than CP and LP during the development of zebrafish. LPS challenge induced up-regulation of all the genes at 12 h in the adult fish. For the larvae, Bf, C3 (key complement component) and C6 (involved in lytic pathway) responded to LPS challenge at earlier stages than the other complement genes, with the up-regulation detected since 14, 14 and 7 dpf, respectively. In the larvae at 28 dpf, all the above three genes responded to LPS challenge by up-regulating their expression in a fashion similar to that of the adult fish, hinting that complement operating via AP develops earlier and plays a key role in protecting the larvae; it showed effective responses to LPS challenge from 14 dpf and might mature before 28 dpf.