Characterization of human FCRL3 ⁺ cells. (A) Gating strategies (sorting scheme) for the separation of human CD4⁺ T cells (conventional memory and naïve T cells and Tregs, top) and CD8⁺ lymphocytes (bottom) from peripheral blood. For conventional CD4⁺ cells, naïve T cells were defined as CD4⁺CD25⁻CD45RA⁺CCR7⁺, while memory cells were CD4⁺CD25⁻CD45RA⁻CD127^+/−. Naïve Tregs were defined as CD4⁺CD25^hiCD127⁻CD45RA⁺CCR7⁺, while memory Tregs were CD4⁺CD25^hiCD127⁻CD45RA⁻CCR7⁺. Naïve CD8⁺ T lymphocytes were sorted as CD8⁺ and CD45RA/CCR7 double-positive, while memory cells were CD8⁺CD45RA^+/−CCR7^+/−. (B) FCRL3 expression in different CD8⁺ T cell subpopulations. Among the CD8⁺ memory cells CD8⁺CD45RA^+/−CCR7^+/−, the subpopulations were defined as T_CM CD8⁺CCR7⁺CD45⁻, T_EM CD8⁺CCR7⁻CD45⁻, and T effector memory reexpressing CD45RA (T_EMRA) CD8⁺CCR7⁻CD45⁺. Each dot represents one donor. N = 3; paired t test, two-tailed. From top to bottom: *P = 0.0365, ****P < 0.0001, n.s. (not significant), P = 0.5185. (C) Pearson’s correlation coefficient between the percentage of CD8⁺ FCRL3⁺ memory T cells and the percentage of CD8⁺ T_EMRA cells across donors. Each dot represents one donor (N = 25). (D) Pearson’s correlation coefficient between the percentage of CD8⁺ FCRL3⁺ memory T cells and the date of birth of the donors. Each dot represents one donor (N = 54). (E) FCRL3 expression in the CD8⁺ T cell effector subsets Tc1 and Tc2. CD8⁺ memory cells CXCR3⁺CCR4⁻ were defined as Tc1, and CXCR3⁻CCR4⁺ cells were defined as Tc2. Each dot represents one donor. N = 3; paired t test, two-tailed. From left to right: *P = 0.0393, **P = 0.0066. T_CM, T central memory; T_EM, T effector memory. Data underlying this figure can be found in Data S4.