OX40L blocking reduces BCL6 induction by TSLP-DC. (A) Quantification of IL-10 production using CBA by CD4 T cells differentiated during 6 d with pDC activated with CpGB (15 µg/ml during 24 h). Anti-ICOSL blocking antibody or isotype control antibody (25 µg/ml) were added at the beginning of the culture. Mean ± SEM for six experiments is plotted. *, P < 0.05 Wilcoxon matched pair test. (B) Quantification by FACS analysis of the percentage of CXCR5^hiPD1^hi, CXCR5^loPD1^lo cells in TSLP-DC co-culture at day 4, treated with functional blocking antibodies or isotype controls as indicated. The percentage of each gate is shown. For BCL6 expression, gray histograms represent the FMO signal, and red histograms represent specific BCL6 staining. MFI of specific staining and percentage of BCL6⁺ cells are plotted for one representative experiment. (C and D) Quantification as in B, from six independent experiments. SMFI for BCL6 was calculated by subtracting the FMO from BCL6-specific staining in CXCR5^hiPD1^hi and CXCR5^loPD1^lo cells. *, P < 0.05; **, P < 0.01; ***, P < 0.001, paired Student’s t test.