IL-12/STAT4 signaling in human tonsillar GC Tfh cells. (A) p-STAT4 expression by GC Tfh cells. Cells expressing p-STAT4 (red) and CD4 (green) in human tonsil were analyzed by confocal microscopy. Blue indicates DAPI staining. DZ, dark zone; FM, follicular mantle; LZ, light zone. Bar equals 100 μm. (B) Nuclear localization of p-STAT4 in Tfh cells is shown on the right with DAPI staining. Bar equals 10 μm. (C) Expression of IL-12Rβ1 on tonsillar GC Tfh (CXCR5^hiICOS^hiCD4⁺ T) cells. (Left) Gating strategy for CXCR5⁻ICOS⁻, CXCR5^loICOS^lo, and CXCR5^hiICOS^hi within CD3⁺CD4⁺ T cells. Representative results from 3 independent experiments. (D) IL-21 secretion by tonsillar GC Tfh cells in response to IL-12. Tonsillar Tfh cells were stimulated for 3 days with autologous SEB-pulsed B cells in the presence of IL-12, IL-23, or type I IFNs. Representative results from 3 independent experiments.