Control of Germinal Center Localization and Lineage Stability of Follicular Regulatory T Cells by the Blimp1 Transcription Factor

Abstract

Summary: Follicular regulatory T (TFR) cells are a specialized suppressive subset that controls the germinal center (GC) response and maintains humoral self-tolerance. The mechanisms that maintain TFR lineage identity and suppressive activity remain largely unknown. Here, we show that expression of Blimp1 by FoxP3+ TFR cells is essential for TFR lineage stability, entry into the GC, and expression of regulatory activity. Deletion of Blimp1 in TFR cells reduced FoxP3 and CTLA-4 expression and increased pro-inflammatory cytokines and spontaneous production of autoantibodies, including elevated IgE. Maintenance of TFR stability reflected Blimp1-dependent repression of the IL-23R-STAT3 axis and activation of the CD25-STAT5 pathway, while silenced IL-23R-STAT3 or increased STAT5 activation rescued the Blimp1-deficient TFR phenotype. Blimp1-dependent control of CXCR5/CCR7 expression also regulated TFR homing into the GC. These findings uncover a Blimp1-dependent TFR checkpoint that enforces suppressive activity and acts as a gatekeeper of GC entry. : Wang et al. identify Blimp1 as a critical transcription factor for the proper positioning and stable expression of the suppressive activity of TFR cells that control GC responses. In the absence of Blimp1, unstable TFR cells prematurely migrate into the GC and differentiate into TFH-like cells to promote dysregulated GC responses. Keywords: humoral tolerance, regulatory T cells, follicular regulatory T cells, follicular helper T cells, germinal center response, germinal center positioning, Blimp1, TFR lineage stability