Figure 1: B cell-derived costimulatory signals promote Tfh differentiation.

(A, B) % CD44^hiCD62L^lo/hi EM (A) and CD44⁺CXCR5⁺ (B) within CD4⁺ compartment in indicated chimeras. (C) FACS plot (gated on CD4⁺; % in gate) show strategy to identify CD44⁺CXCR5⁺ T cells. Histograms show Tfh markers PD1, ICOS, CCR7, and BCL-6 in CD44⁺CXCR5⁺CD4⁺ T cells from WAS (solid line) and B cell-intrinsic Cd80^−/−.Cd86^−/− WAS (dashed line) chimeras. Gray histogram: CD44⁻CXCR5⁻ naïve CD4⁺ T cells. Graphs: MFI of indicated markers (normalized to WAS chimera for each independent experiment) in WAS (open circle) and B cell-intrinsic Cd80^−/−.Cd86^−/− WAS (solid circle) chimeras. (D) Splenic CD44⁺CXCR5^hiPD1^hiICOS^hi “GC” Tfh cells (Left: % of CD4⁺; Right: number). (A-D) *, P<0.05; **, P<0.01; ***, P<0.001; ****, P<0.0001, by one-way ANOVA and Tukey’s multiple comparison test (A, B, D), and by two-tailed Student’s t test (C). Each data point indicates individual animal.