IL-7 enhances T cell–DC interactions. (A) Histogram shows class II MHC expression by F5 T cells recovered from spleen 7 days after transfer to Il7^−/−Rag1^−/− (broken line) or Rag1^−/− (solid line) hosts (n = 5 per group) compared with F5 T cells from control F5 mice (gray fill). Graph shows I-A^b staining after transfer to Rag1^−/− (■) or Il7^−/−Rag1^−/− hosts (□) as percentage of expression by F5 T cells from control mice. Data are representative of 3 or more experiments. (B) CD45.1⁺ IL-7R⁺ and CD45.1⁻ IL-7R⁻ F5 T cells were cotransferred to Rag1^−/− hosts (n = 4) and cells analyzed for class II MHC expression 1 day later. Histograms show I-A^b staining by IL-7R⁺ and IL-7R⁻ F5 T cells before (broken line) and after (solid line) transfer to Rag1^−/− hosts. Bar chart is MFI of I-A^b staining by the indicated F5 T cell donor after transfer to Rag1^−/− hosts (*P < .02).