Infectious Tolerance Require IL-35 To Mediate Suppression and Cutting Edge: Human Regulatory T Cells

Human regulatory T cells (T reg) are essential for the maintenance of immune tolerance. However, the mechanisms they use to mediate suppression remain controversial. Although IL-35 has been shown to play an important role in T reg-mediated suppression in mice, recent studies have questioned its relevance in human T reg. In this study, we show that human T reg express and require IL-35 for maximal suppressive capacity. Substantial upregulation of EBI3 and IL12A, but not IL10 and TGFB, was observed in activated human T reg compared with conventional T cells (T conv). Contact-independent T reg-mediated suppression was IL-35 dependent and did not require IL-10 or TGF-b. Lastly, human T reg-mediated suppression led to the conversion of the suppressed T conv into iTr35 cells, an IL-35–in-duced T reg population, in an IL-35–dependent manner. Thus, IL-35 contributes to human T reg-mediated suppression , and its conversion of suppressed target T conv into IL-35–induced T reg may contribute to infectious tolerance. I nterleukin-35 (EBI3–IL-12a [IL12A] heterodimer) is required for murine regulatory T cells (T reg) function (1) and has been shown to induce the conversion of murine and human conventional T cells (T conv) into IL-35–induced T reg (iTr35) (2). Furthermore, IL-35 is produced by human T conv exposed to rhinovirus-infected dendritic cells (3) and human peripheral blood CD4 + T cells from chronic hepatitis B virus-infected patients (4). However, two studies have suggested that human T reg neither express nor produce IL-35, increasing the controversy surrounding the physiological importance of IL-35 in human T reg (5, 6). Several studies have shown that both murine and human T reg can mediate infectious tolerance, the contagious spread of suppressive capacity from T reg to the suppressed target cell. The mechanisms used to mediate this induction and the subsequent mechanisms used by this induced regulatory population to mediate suppression remain obscure (7–9). However, studies with human T reg have suggested that IL-10 and TGF-b may contribute to these events (10, 11). Nevertheless, mechanistic insight into the regulatory preferences of human T reg is lacking. Cell isolation, expansion, and labeling CD4 + T cells were obtained and purified from human cord blood or apha-seresis rings, as previously described (2, 12). Purity was verified by in-tracellular staining of FOXP3 (eBioscience, San Diego, CA). T reg and T conv were expanded in X-VIVO medium containing beads coated with anti-CD3 and anti-CD28 (bead/cell ratio 1:1), 20% (v/v) human sera …