Figure 6.

Human T1D patients have decreased serum sCD137 levels, and sCD137 is secreted from human regulatory T cells. Human sCD137 suppresses human T cell proliferation. (A) sCD137 concentration in serum from pediatric type 1 diabetic patients (n = 11) or age-matched controls without T1D (n = 10) (all subjects were ages 2–18 years) was measured by ELISA. ^*p = 0.03, unpaired t-test. (B) Human CD4+CD25^lowCD127^high conventional T cells (Tconvs), CD4+CD25^highCD127^high double positive T cells (Tdps), and CD4+CD25^highCD127^low regulatory T cells (Tregs) from healthy donors were stimulated as indicated for 72 h. Supernatant was collected and human sCD137 concentration measured by ELISA. Data were expressed as mean/SEM from four subjects. ^*p < 0.01 vs. Tconv in each dose of IL-2, ^†p < 0.01 vs. Tdp in each dose of IL-2, unpaired t-test. n.d., not detected. (C) carboxyfluorescein succinimidyl ester (CFSE)–labeled human CD4+ Tconv cells were stimulated with CD3/28 dynabeads in the presence or absence of hu-sCD137 for 3 days. CFSE dilution was analyzed on FACSCanto. One representative histogram (left panel) of CFSE is shown. Percentages of cells with the indicated number of cell divisions (gated as shown in the histogram) are shown in the right bar graph. Data expressed as average/SEM of n = 5 independent samples ^*p < 0.01, unpaired t-test.