Expression of Foxp3 by T follicular helper cells in end-stage germinal centers

Regulating germinal center contraction Germinal centers (GCs) in secondary lymphoid organs are where mature B cells expand and differentiate. Although GC formation is well studied, the control of GC duration and contraction is less well understood. Using intravital imaging of mouse GCs and single-cell RNA sequencing, Jacobsen et al. report that T follicular helper (T FH ) cells are a critical player in this process. They found that some late-GC T FH cells upregulate the transcription factor FOXP3 and acquire a regulatory T cell–like phenotype. These cells are distinct from T follicular regulatory (T FR ) cells and, unlike T FR cells, are needed to shut down the GC reaction. Tweaking this process may be key to extending GC lifetimes and enhancing antibody responses in the context of vaccination. Science , abe5146, this issue p. eabe5146