Preparation of the monoclonal antibody against Nile tilapia Igλ and study on the Igλ B cell subset in Nile tilapia.

Immunoglobulins (Igs) are important effector molecules that mediate humoral immunity. A typical Ig consists of two heavy and two light chains. In teleosts, three Ig heavy chain isotypes (Igμ, Igδ and Igτ) and three Ig light chain isotypes (Igκ, Igλ and Igσ) have been identified. Compared to the heavy chains, teleost Ig light chains have been poorly studied due to the lack of antibodies. In this study, a mouse anti-Nile tilapia Igλ monoclonal antibody (mAb) was prepared, which could specifically recognize Igλ in serum and Igλ B cells in tissues. Further, the composition of IgM and Igλ B cell subsets was analyzed using this antibody and a mouse anti-tilapia IgM heavy chain mAb. The ratio of IgMIgλ B cells to total IgM B cells in head kidney and peripheral blood was about 30%, while that in spleen was about 50%; the ratio of IgMIgλ B cells to total Igλ B cells in head kidney and peripheral blood was about 45%, while that in spleen was about 25%. The IgMIgλ B cells was speculated to be IgT B cells. Finally, we detected an increase in the level of specific antibodies against the surface antigen-Sip of Streptococcus agalactiae in serum after S. agalactiae infection, indicating that mouse anti-tilapia Igλ mAb can be used to detect the antibody level after immunization of Nile tilapia, which lays a foundation for the evaluation of immunization effect of tilapia vaccine.