A rare subset of skin-tropic regulatory T cells expressing Il10/Gzmb inhibits the cutaneous immune response

Abstract

Abstract We reported that Foxp3+ regulatory T cells (Tregs) migrating from the skin to the draining lymph node have a strong immunosuppressive effect on contact hypersensitivity (CHS) response. However, the Treg subsets that regulate the CHS response remain poorly defined. In this study, we used a combination of single-cell real-time PCR high-dimensional gene expression profiling data with spatiotemporal information about cellular movement from the mice expressing the photoconvertible protein KikGR to elucidate the role and characteristics of Treg subsets in CHS response. We found that although immunosuppressive genes Ctla4 and Tgfb1 were expressed in the majority of Tregs, Il10-expressing Tregs were rare and unexpectedly, the majority of Il10-expressing Tregs co-expressed Gzmb and displayed Th1-skewing. Furthermore, Gzmb-/Il10-expressing Treg subsets expressed the novel markers CD43 and CCR5. CD43+ CCR5+ CXCR3− Tregs highly expressed skin-tropic chemokine receptors CCR4 and CCR8. We also measured the retention of Treg subsets within inflamed skin using KikGR mice, and found that the subset of Tregs that was most highly retained in the skin, CD43+ CCR5+ CXCR3− Tregs, had superior in vivo inhibitory function to other Treg subsets. These results suggested that even if only present in small numbers, highly activated Tregs that co-express Gzmb and Il10 and that have the capacity to remain in inflamed tissue are likely to be clinically relevant due to the role of these molecules in the control of excessive immune responses. Taken together, the identification of a rare Treg subset co-expressing multiple immunosuppressive molecules and having tissue-remaining capacity offers a novel strategy for the control of skin inflammatory responses.