Reduced activation of FCRL3 ⁺ T cells. (A) Surface FCRL3 expression measured by FACS in human naïve and memory CD4⁺ T helper, Tregs, and CD8⁺ T lymphocytes freshly isolated from peripheral blood of one representative healthy donor. (B) FCRL3 expression in different T cell populations measured as in A. Each dot represents one donor. N = 6–9; mean ± SD; paired t test, two-tailed. From left to right: **P = 0.0033, *P = 0.0303, *P = 0.0255. (C–E) Surface staining for CD25 (C), OX40 (D), and CD40L (E) expression in sorted FCRL3⁺ and FCRL3⁻CD8⁺ memory T cells after stimulation with plate-bound anti-CD3/CD28 for 48 h. Each dot represents a different donor, N = 4–10. Mean, paired t test or ratio paired t test, two-tailed. From left to right: (C)***P = 0.0008, ***P = 0.0003, (D)*P = 0.048, **P = 0.0071, (E)**P = 0.0064, **P = 0.0044. Data underlying this figure can be found in Data S4.