IL-33 Receptor-Expressing Regulatory T Cells Are Highly Activated, Th2 Biased and Suppress CD4 T Cell Proliferation through IL-10 and TGFβ Release

Immunomodulatory Foxp3(+) regulatory T cells (Tregs) form a heterogeneous population consisting of subsets with different activation states, migratory properties and suppressive functions. Recently, expression of the IL-33 receptor ST2 was shown on Tregs in inflammatory settings. Here we report that ST2 expression identifies highly activated Tregs in mice even under homeostatic conditions. ST2(+) Tregs preferentially accumulate at non-lymphoid sites, likely mediated by their high expression of several chemokine receptors facilitating tissue homing. ST2(+) Tregs exhibit a Th2-biased character, expressing GATA-3 and producing the Th2 cytokines IL-5 and IL-13 -especially in response to IL-33. Yet, IL-33 is dispensable for the generation and maintenance of these cells in vivo. Furthermore, ST2(+) Tregs are superior to ST2(-) Tregs in suppressing CD4(+) T cell proliferation in vitro independent of IL-33. This higher suppressive capacity is partially mediated by enhanced production and activation of the anti-inflammatory cytokines IL-10 and TGF beta. Thus, ST2 expression identifies a highly activated, strongly suppressive Treg subset preferentially located in non-lymphoid tissues. Here ST2(+) Tregs may be well positioned to immediately react to IL-33 alarm signals. Their specific properties may render ST2(+) Tregs useful targets for immunomodulatory therapies.