The expansion in lymphoid organs of IL-4 ⁺ BATF ⁺ T follicular helper cells is linked to IgG4 class switching in vivo

Distinct T follicular helper (T FH ) subsets that influence specific class-switching events are assumed to exist, but the accumulation of isotype-specific T FH subsets in secondary lymphoid organs (SLOs) and tertiary lymphoid organs has not been hitherto demonstrated. IL-4–expressing T FH cells are surprisingly sparse in human SLOs. In contrast, in IgG4-related disease (IgG4-RD), a disorder characterized by polarized Ig class switching, most T FH cells in tertiary and SLOs make IL-4. Human IL-4 + T FH cells do not express GATA-3 but express nuclear BATF, and the transcriptomes of IL-4–secreting T FH cells differ from both PD1 hi T FH cells that do not secrete IL-4 and IL-4–secreting non-T FH cells. Unlike IgG4-RD, IL-4 + T FH cells are rarely found in tertiary lymphoid organs in Sjögren’s syndrome, a disorder in which IgG4 is not elevated. The proportion of CD4 + IL-4 + BATF + T cells and CD4 + IL-4 + CXCR5 + T cells in IgG4-RD tissues correlates tightly with tissue IgG4 plasma cell numbers and plasma IgG4 levels in patients but not with the total plasma levels of other isotypes. These data describe a disease-related T FH subpopulation in human tertiary lymphoid organs and SLOs that is linked to IgG4 class switching.