Genome-wide analysis identifies Bcl6 repression of the IL-7R/STAT5 axis during T follicular helper (Tfh) cell differentiation

T follicular helper (Tfh) cell is a unique T cell subset specialized in promoting germinal center reactions. Bcl6 has been identified as an obligatory transcription factor in Tfh cells; however, the molecular mechanism underlying Bcl6 function still remains unknown. Here, we combined genome-wide Bcl6 occupancy and transcriptome profiling to systemically analyze Bcl6 targets in Tfh cells. We found that Bcl6 exhibits unique binding preferences in Tfh cells from those in Th9, B cells and macrophage and its binding is closely associated with decrease in 5-hydroxymethylcytosine (5hmC). Importantly, Bcl6 directly binds to the IL-7R/CD127 gene and suppresses its expression. Bcl6 also binds the same sequences recognized by signal transducer and activator of transcription (STAT) 5, downstream of IL-7R. Bcl6 promotes CD127loPDhi Tfh cell differentiation; deletion of the Bcl6 gene in T cells results in enhanced IL-7R-STAT5 signaling and substantial expansion of CD127hiPDlo non-Tfh cells. Our study thus systemically examines Bcl6-controlled regulatory networks and provides novel insights into its biological functions in Tfh cells. Examination of Bcl6 binding profile in Tfh cells.