BAFF gets involved in response to bacterial infection and promotes IgM+ B cell survival in Nile tilapia (Oreochromis niloticus)

Abstract B-cell activating factor (BAFF), a member of the tumor necrosis factor (TNF) ligand family, is known to play a notable role in the survival and differentiation of B cells. In this study, we conducted functional analysis of BAFF in Nile tilapia (Oreochromis niloticus). Expression analysis revealed that OnBAFF was widely distributed in all tested tissues but expressed highly in the spleen. Analysis of sorted IgM positive (IgM+) and IgM negative (IgM−) lymphocyte populations from spleen and head kidney, the results indicated that OnBAFF had a high expression in the IgM+ B cells. In addition, in vivo, the OnBAFF expression was significantly up-regulated in spleen and head kidney after challenges of Streptococcus agalactiae (S. agalactiae) and lipopolysaccharide (LPS), and the similar significant up-regulation of OnBAFF was also observed in the spleen and head kidney leukocytes after stimulations with these two different immunogens in vitro. Furthermore, the recombinant OnBAFF ((r)OnBAFF) protein could improve the survival rate of IgM+ B cells in vitro. Moreover, the transcription levels of OnBAFF receptors were detected in IgM+ B cells, revealing that the OnBAFF-R and OnTACI were expressed much higher in the IgM+ B cells. Taken together, this study indicated that OnBAFF might get involved in host immune resistance against bacterial infection and promote IgM+ B cell survival in Nile tilapia.