Regulation of B cell function and expression of CD11c, T-bet, and FcRL5 in response to different activation signals

Abstract CD11c, FcRL5, or T-bet are commonly expressed by B cells expanding during inflammation, where they can make up >30% of mature B cells. However, the association between the proteins and differentiation and function in the host response remain largely unclear. We have assessed the co-expression of CD11c, T-bet and FcRL5 in an in vitro B cell culture system to determine how stimulation via the B cell receptor (BCR), toll-like receptor 9 (TLR9), and different cytokines influence CD11c, T-bet, and FcRL5 expression. We observed different expression dynamics for all markers, but a largely overlapping regulation of CD11c and FcRL5 in response to BCR and TLR9 activation, while T-bet was strongly dependent on IFN-γ signalling. Investigating plasma cell differentiation and antigen-presenting cell (APC) functions, there was no association between marker expression and antibody secretion or T cell help. Rather the functions were associated with TLR9-signalling and B cell-derived IL-6 production, respectively. These results suggest that the expression of CD11c, FcRL5, and T-bet and plasma cell differentiation and improved APC functions occur in parallel and are regulated by similar activation signals, but that they are not interdependent.