Cutting Edge: Bcl6-Interacting Corepressor Contributes to Germinal Center T Follicular Helper Cell Formation and B Cell Helper Function.

CD4(+) germinal center (GC)-T follicular helper (Tfh) cells help B cells become long-lived plasma cells and memory cells. The transcriptional repressor Bcl6 plays a key role in GC-Tfh formation by inhibiting the expression of genes that promote differentiation into other lineages. We determined whether BCOR, a component of a Polycomb repressive complex that interacts with the Bcl6 BTB domain, influences GCTfh differentiation. T cell-targeted BCOR deficiency led to a substantial loss of peptide: MHC class II-specific GC-Tfh cells following Listeria monocytogenes infection and a 2-fold decrease following immunization with a peptide in CFA. The reduction in GC-Tfh cells was associated with diminished plasma cell and GC B cell formation. Thus, T cell-expressed BCOR is critical for optimal GC-Tfh cell differentiation and humoral immunity.