Expression and characterization of Nile tilapia (Oreochromis niloticus) secretory and membrane-bound IgM in response to bacterial infection

Abstract IgM, the predominant immunoglobulin in teleost, plays an important role in host defense against pathogen infection. In this study, Nile tilapia ( Oreochromis niloticus ) secretory ( s-IgM ) and membrane-bound IgM ( m-IgM) genes were characterized at expression patterns against bacterial infection in vivo and in vitro. Expression analysis revealed that both s-IgM and m-IgM were highly expressed in head kidney, spleen and mucosal tissues such as intestine and gill. Both IgM mRNA expressions were significantly up-regulated in the head kidney, spleen, intestine and gill following Streptococcus agalactiae ( S. agalactiae ) challenge . The significant up-regulations of both IgM expressions were also detected at the protein level with the analyses of western blotting and immunofluorescence detection. In addition, inducement with the S. agalactiae in vitro caused significant increases in expressions of both s-IgM and m-IgM . The IgM concentrations in serum and cell supernatant were both significantly increased after S. agalactiae stimulation by ELISA analysis. Taken together, the present study of IgM characterization indicated that IgM played an important role in host defense against bacterial infection in Nile tilapia.