Bcl6 Protein Expression Shapes Pre-Germinal Center B Cell Dynamics and Follicular Helper T Cell Heterogeneity

SummaryThe transcription factor Bcl6 is essential for the development of germinal center (GC) B cells and follicular helper T (Tfh) cells. However, little is known about in vivo dynamics of Bcl6 protein expression during and after development of these cells. By using a Bcl6 reporter mouse strain, we found that antigen-engaged B cells upregulated Bcl6 before clustering in GCs. Two-photon microscopic analysis indicated that Bcl6 upregulation in pre-GC B cells contributed to sustaining their interactions with helper T cells and was required for their entry to GC clusters. Our data also suggested that Tfh cells gradually downmodulated Bcl6 protein over weeks after development. The Bcl6-low Tfh cells rapidly terminated proliferation and upregulated IL-7 receptor. These results clarify the role of Bcl6 in pre-GC B cell dynamics and highlight the modulation of Bcl6 expression in Tfh cells that persist in the late phase of the antibody response.

Graphical AbstractFigure optionsDownload full-size imageDownload high-quality image (316 K)Download as PowerPoint slideHighlights► Antigen-engaged B cells upregulate Bcl6 in the outer follicle to enter GC clusters ► Bcl6 in pre-GC B cells is important for sustaining conjugation with helper T cells ► Bcl6 protein is downmodulated in a number of Tfh cells after their development ► Bcl6-low Tfh cells rapidly terminate proliferation and upregulate IL-7 receptor