NFAT1 deficiency is associated with impaired T_FHfunction. (A) Expression of activation markers in CD4⁺ memory T cells after P/I treatment, including CD69, PD-1, CD40L, CD25, and ICOS. Mean fluorescence intensities are indicated. (B) Frequency of circulating T_FH cells in PD-1⁺ memory CD4⁺ T cells in the patient and a representative control. (C) Quantification of B. (D) CD40L and IL-21 expression in patient and control cT_FH cells after 4 hours of P/I stimulation. (E-F) Quantification of D. (G) Frequency of CD40L⁺ and TNF-α⁺ GFP⁺ CD4⁺ patient or control memory T cells after 4 hours of P/I stimulation of EV or WT NFATC2 transduction. (H-I) Quantification of G. ∗P < .05, ∗∗P < .01, ∗∗∗P < .001, ∗∗∗∗P < .0001, one-way analysis of variance and Tukey’s post-hoc test. NS, not significant. Green circles, healthy control; blue circle, II-2; blue upright triangle, I-2; blue inverted triangle, I-1; blue square, II-3; red/purple diamond, II-1.