Variable dependency on BAFF in IgG antibody production during Leishmania infection.

B-cell activating factor (BAFF) is known as a cytokine responsible for survival and activation of B cells. However, involvement of the molecule in IgG antibody production during infection remains elusive. In this study, dependency of antibody production in Leishmania infection on BAFF was examined by using BAFF-knockout (BAFF-KO) mice. When BAFF-KO mice were infected with L. major, there was no significant difference in lesion development or parasite burden from those in infected wildtype mice. In contrast, levels of IgG antibodies to Leishmania crude antigen were lower in BAFF-KO mice, suggesting that antibody production during L. major infection is BAFF-dependent. ELISA using defined leishmanial antigens demonstrated that the influence of BAFF on antibody production during L. major varies depending on antigens; IgG production to tandem repeat proteins were more affected by BAFF than non-repeat antigens. On the contrary, all of the defined antigens tested were strongly affected by BAFF for IgG antibody production during L. donovani infection. These results suggest degree of BAFF contribution to antibody production during infection is variable depending on the type of infection and even on the type of antigen in a given infection. These results may explain contradictory roles of BAFF in antibody production in previous works.