FIGURE 6.

T cells, and not APCs, mediate the primary effects of IL-6 on reversal of Treg-induced suppression. CD4⁺CD25^– T cells and CD4⁺CD25^high Tregs were isolated from peripheral blood of healthy volunteers. Cells were cocultured with either allogeneic APCs or anti-CD3/anti-CD28 Abs as indicated. A and B, Supernatants were removed from cocultures at indicated time points and assayed for cytokine production by ELISA. Neutralizing Abs against IL-6Rα and gp130 were included at 1 μg/ml in B. Results shown are mean of three experiments ± SEM. C, T cells were cultured with allogeneic APCs, 25 ng/ml sIL-6R, and with or without 10 ng/ml rhIL-6 as indicated. Cells were back-sorted from cocultures at 48 h, and protein lysates were probed for pStat3 and β-actin. The immunoblot shown is representative of two separate experiments. D, CD25^– T cells (“Teff”) or CD25^high Tregs were pretreated for 16 h with Stattic V and then washed and cocultured together with indicated concentrations of rhIL-6 and 25 ng/ml sIL-6R. Results shown are mean of three experiments ± SEM, and p values were adjusted using the Bonferroni method.