IL-7–induced proliferation of adult naive CD4⁺ T cells is restricted to the CD31⁺ subset. (A) Representative dot-plots of CD31 and Ki67 flow cytometry analysis after 7-day culture in the presence of IL-7 of purified CD31⁺ and CD31⁻ naive CD4⁺ T-cell subsets from adult peripheral blood, for an IL-7 “nonresponder” (top panel), an IL-7 “responder” (middle panel), and CB (bottom panel). Cells were successively gated on a viable lymphogate, CD3⁺, CD4⁺, and CD45RA⁺. (B) CD31 MFI was assessed within the purified CD31⁺ naive subset further gated on Ki67⁺ or Ki67⁻ cells after 7-day culture with IL-7. Three adults and 4 CB samples were studied. (C) Representative dot-plot illustrating CD31 expression plotted against CFSE labeling of CB CD4⁺CD45RA⁺ T cells cultured with IL-7 for 7 days. CD31⁺ cells were further gated according to the number of cell divisions, and bars show CD31 MFI from 4 experiments. (D) Ex vivo analysis of IL-7Rα MFI on freshly isolated mononuclear cells from adult and CB samples sequentially gated on CD3⁺, CD4⁺, CD45RA⁺, and CD31⁺ or CD31⁻ lymphocytes. Each symbol represents one individual. Bars represent mean plus or minus SEM. Data were compared using paired or unpaired t test as appropriate and significant P values are shown.