T-cell-derived IFN-γ suppresses T follicular helper cell differentiation and antibody responses.

CD4 T cells play a critical role in antiviral humoral and cellular immune responses. We have previously reported that subcutaneous lymphocytic choriomeningitis virus (s.c. LCMV) infection is characterized by a stark compartmentalization of CD4 T cells, leading to strong T1 cell polarization but virtually absent T follicular helper (T) cells, key drivers of humoral immunity. Here, we investigate the mechanisms responsible for this impaired T differentiation. We show that T-bet cells induced by LCMV infection encompass a T1 cell subset expressing granzyme B (GzmB), and a Tcf-1 cell subset that retains the potential for T differentiation without expressing mature T markers. Notably, IFN-γ blockade enables full differentiation of Tcf-1 cells into T cells, formation of germinal centers, and increased antibody production. Suppression of T cells by IFN-γ is not directly mediated by CD4 T cells but rather involves another cell type, likely dendritic cells (DCs). Our study provides novel insights into the mechanisms underlying early CD4 T-cell polarization and humoral responses to viruses, with the potential to facilitate the development of effective vaccine strategies.