ALPS patients (but not asymptomatic, mutation-positive carriers) display decreased circulating memory B-cell counts, which correlate with levels of lymphoproliferation markers. The proportion of memory B cells (CD19⁺CD27⁺ cells) (A-B), MZ B cells (CD19⁺CD27⁺IgD⁺) (C-D), and SM B cells (CD19⁺CD27⁺IgD⁻) in healthy controls, ALPS patients, and asymptomatic MPRs (E-F). Values are plotted as a function of age for each group in panels B, D, and F. ns, nonsignificant. *P < .05; ***P < .001. In panels B, D, and F, healthy donors are plotted in green, ALPS patients in red, and MPR in black. Proportions of memory B cells CD19⁺CD27⁺ (G) and MZ B cells CD19⁺CD27⁺IgD⁺ (H) are depicted as a function of disease activity (nontreated patients with active disease, treated patients, and patients in remission) and compared with the values in asymptomatic MPRs. The proportion of CD19⁺CD27⁺ memory B cells was inversely correlated with (I) the proportion of circulating DN-Ts (CD3⁺TCRαβ⁺CD4⁻CD8⁻) and (J) the plasma FAS-L concentration (ng/L). *P < .05; **P < .01.