BAFF upregulates CD28/B7 and CD40/CD154 expression and promotes mouse T and B cell interaction in vitro via BAFF receptor

Aim: B cell-activating factor belonging to the TNF family (BAFF) is a member of TNF family and required for peripheral B cell survival and homeostasis. BAFF has been shown to promote the proliferation of T and B cells. In this study we examined whether and how BAFF mediated the interaction between mouse T and B cells in vitro. Methods: BAFF-stimulated B or T cells were co-cultured with T or B cells. The interactions between T and B cells were analyzed by measuring the expression of co-stimulatory molecules (CD28/CD80 or CD40/CD154), the proliferation and secretion of T and B cells and other factors. Two siRNAs against the transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) and BAFF receptor (BAFF-R) were used to identify the receptors responsible for the actions of BAFF. Results: BAFF-stimulated B cells significantly promoted the proliferation and activity of co-cultured T cells, and increased the percentages of CD4(+)CD28(+) and CD4(+)CD154(+) T cells. Similarly, BAFF-stimulated T cells significantly promoted the proliferation and activity of co-cultured B cells, and increased CD19(+)CD80(+) and CD19(+)CD40(+) B cell subpopulations. BAFF-R siRNA-silenced B cells showed significantly lower expression of CD40 and CD80 than the control B cells. When the BAFF-R siRNA-silenced B cells were stimulated with BAFF, then co-cultured with T cells, the expression of CD28 and CD154 on T cells was not increased. TACI siRNAsilenced B cells exhibited higher expression of CD40 and CD80 than the control B cells. When the TACI siRNA-silenced B cells were stimulated with BAFF, then co-cultured with T cells, the expression of CD28 and CD154 on T cells was significantly increased. Conclusion: BAFF upregulates CD28/B7 and CD40/CD154 expression, and promotes the interactions between T and B cells in a BAFFR- dependent manner.