Molecular cloning of IgT, IgD and analysis the IgH locus in largemouth bass (Micropterus salmoides) and immune response upon bacterial infection

Immunoglobulins (Igs) are crucial components of the immune response in vertebrates including teleost fish. In the present study, we firstly cloned the full-length cDNA of IgT and IgD heavy chain genes in largemouth bass (Micropterus salmoides), one of the important farmed fish species in China. Importantly, IgH locus covering tau, mu and delta genes of largemouth bass was also illustrated. The genomic organization of the IgH locus presented as V-26-D-3-J(5)-C-tau-D-6-J(6)-C-mu-C-delta, which was similar with some other teleost fish. Furthermore, The IgH locus of largemouth bass contained 26 VH segments and they belonged to three subgroups, whose members showed a greater than 80% amino acid identity. This founding would allow us to gain further insight into the evolution of adaptive immune system. To further understanding the immune response of immunoglobulins, we successfully constructed the infection model with bacteria (GFP Flavobacterium columnare G(4)). Our results showed the expression of IgM was up-regulated in head kidney, and the expression of IgT was significantly induced mainly in skin and gill, suggesting their potential roles in systemic and mucosal immune response to bacterial infection, respectively.