Deconstructing T-B Interactions by Manipulation of IRF4 to Understand Regulation of T Follicular Helper Cells

Abstract Germinal center (GC) derived high affinity antibody is important for protecting against infectious disease. Interactions between T follicular helper (Tfh) cells and GC B cells are requisite for affinity maturation. While it is clear that bi-directional signals are important for the generation of Tfh and GC B cells, a full understanding of the signaling dynamics that lead to efficient T and B cell differentiation is not known. Studying these B cell-derived signals and their role in Tfh cell commitment, maintenance, and function during GC reactions will lead to an improved understanding of this tightly regulated system. The transcription factor IRF4 is necessary and sufficient for generating GC B and plasma cell fates through graded expression. We have shown previously through gene ontology analysis that IRF4 targets include genes involved in T and B cell interaction. This raises the possibility that beyond cell-specific control of B cell fates, IRF4-regulated genes in B cells may facilitate interactions between B and T cells. We hypothesize that IRF4 controls a gene program in B cells necessary to generate efficient T cell activation and Tfh cell differentiation. Using in-vitro co-culture, we assessed changes in T and B cell activation and functionality by flow cytometry. We found that Irf4−/− B cells processed antigen poorly and led to quantitatively and qualitatively reduced T cell activation compared to Irf4+/+ B cells. This indicates a major role for IRF4 in controlling a B cell gene program necessary for efficient T cell activation. We are currently investigating the nature of these signals through in-vitro and in-vivo approaches in order to deconstruct the molecular nature of T-B interactions during the GC program.