Primary germinal center-resident T follicular helper cells are a physiologically distinct subset of CXCR5PD-1 T follicular helper cells.

T follicular helper (Tfh) cells are defined by a Bcl6CXCR5PD-1 phenotype, but only a minor fraction of these reside in germinal centers (GCs). Here, we examined whether GC-resident and -nonresident Tfh cells share a common physiology and function. Fluorescently labeled, GC-resident Tfh cells in different mouse models were distinguished by low expression of CD90. CD90 GCTfh cells required antigen-specific, MHCII B cells to develop and stopped proliferating soon after differentiation. In contrast, nonresident, CD90 Tfh (GCTfh-like) cells developed normally in the absence of MHCII B cells and proliferated continuously during primary responses. The TCR repertoires of both Tfh subsets overlapped initially but later diverged in association with dendritic cell-dependent proliferation of CD90 GCTfh-like cells, suggestive of TCR-dependency seen also in TCR-transgenic adoptive transfer experiments. Furthermore, the transcriptomes of CD90 and CD90 GCTfh-like cells were enriched in different functional pathways. Thus, GC-resident and nonresident Tfh cells have distinct developmental requirements and activities, implying distinct functions.