Identification of tonsillar CD4 + CD25 - LAG3 + T cells as naturally occurring IL-10-producing regulatory T cells in human lymphoid tissue.

IL-10-producing regulatory T cells (IL-10-producing Tregs) are one of the regulatory T cell subsets characterized by the production of high amounts of IL-10, the lack of FOXP3 expression and the strong immunosuppressive capabilities. IL-10-producing Tregs have been primarily reported as induced populations thus far, in part because identifying naturally occurring IL-10-producing Tregs was difficult due to the lack of definitive surface markers. Lymphocyte-activation gene 3 (LAG3) is a CD4 homologue that we have identified as being expressed on IL-10 producing Tregs. In human PBMC, LAG3 combined with CD49b efficiently identifies IL-10-producing Tregs. However, naturally occurring IL-10-producing Tregs in human secondary lymphoid tissue have not been described. In this report, we identified CD4 ⁺ CD25 ^- LAG3 ⁺ T cells in human tonsil. This T cell subset produced high amounts of IL-10 and expressed low levels of FOXP3. Surface markers and microarray analysis revealed that this is a distinct tonsillar CD4 ⁺ T cell subset. CD4 ⁺ CD25 ^- LAG3 ⁺ T cells expressed interleukin 10 (IL10), PR/SET domain 1 (PRDM1), and CD274 at high levels and chemokine receptor 5 (CXCR5) at low levels. CD4 ⁺ CD25 ^- LAG3 ⁺ T cells suppressed antibody production more efficiently than CD4 ⁺ CD25 ⁺ T cells, and CD4 ⁺ CD25 ^- LAG3 ⁺ T cells induced B cell apoptosis. Moreover, analysis of humanized mice revealed that this cell subset suppressed a graft-versus-host disease (GVHD) reaction in vivo. Our study reveals the existence of naturally occurring IL-10-producing Tregs in human secondary lymphoid tissue and their function in immune regulation.
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