IL-7–induced up-regulation α4β7 is unrelated to expression of the IL-7 receptor and depends on activation of both the JAK-STAT and PI3K signaling pathways. (A) Expression of the α-chain of the IL-7 receptor (CD127) in naive, memory α4β7⁺ and memory α4β7⁻ CD4⁺ T cells as evaluated by flow cytometry in purified CD4⁺ T cells cultured for 24 hours in the presence or absence of IL-7 at 5 ng/mL. The shaded histograms denote the staining of IL-7–treated cells; the empty profiles denote the staining of untreated cells. (B) Inhibition of IL-7–mediated α4β7 induction in naive, CM and EM CD4⁺ T cells by specific Stat5 or PI3K inhibitors. Both inhibitors were used at 50μM; the cells were analyzed by flow cytometry using mAb Act-1 after 24 hours of culture in the presence of IL-7. Because both inhibitors were dissolved in DMSO, cells cultured in the absence of inhibitors were treated with equivalent amounts of DMSO (1:1000 vol/vol). The different CD4⁺ T-cell subsets were separately analyzed based on the expression of CD45RA, CD45RO, CD62L, and CCR7. The shaded histograms denote the staining of cytokine-treated cells; the empty profiles denote the staining of control, untreated cells. (C) Phosphorylation of Stat5 (P-STAT) in purified naive and memory CD4⁺ T lymphocytes exposed to different doses of IL-7 as tested by Western blot at various time points over a period of 24 hours. Time 0 indicates the baseline levels of expression before IL-7 treatment. The total amount of Stat protein (STAT) was measured in parallel in the same samples. Data are representative of at least 3 independent experiments performed with similar results.