IL-7 and Treg proliferative history. (A) CD4+CD25high T regulatory cells (Tregs) were quantified using flow cytometry in peripheral blood mononuclear cells (PBMCs) from 30 patients in clinical remission (CR) as a proportion of total CD4+ T cells. A direct correlation between the frequency of CD4+CD25highTregs and serum interleukin (IL)-7 was observed (rho = 0.647, P <0.0001). (B) Flow cytometry strategy T cells (CD25low) and naïve T cells (CD25− cells). The panel describes further the gating strategy used for cell sorting of naïve cells (bottom 30% of CD25−cells), effector cells (middle 30% of CD25+cells) and Tregs (top 75% of CD25highcells). (C) T-cell subsets were sorted from 21 CR patients using the gates described in Figure 2B. DNA was extracted and T-cell receptor excision circle (TREC) content measured by real-time PCR. TREC levels in both naïve and Treg subsets were high, suggesting a short proliferative history, but lower in the effector subset, indicating several rounds of proliferation. There was a positive correlation between in vivo IL-7 levels and TREC content of naïve T cells (rho = 0.745, P <0.002).