Highlights d Intravenous administration of an agonistic anti-CD40 antibody induces early IL-10 d IL-10 levels in the plasma correlate with CD103 + T RM s in the lung d Blocking IL-10 in vitro or in vivo reduces CD103 + T RM s d Monocyte-derived IL-10 induces TGF-b release and CD103 upregulation on naive T cells

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Recent studies have highlighted that human resident memory T cells (TRM) are functionally distinct from circulating T cells. Thus, it can be postulated that skin T cells age differently from blood-circulating T cells. We assessed T-cell density, diversity, and function in individuals of various ages to study the immunologic effects of aging on human skin from two different countries. No decline in the density of T cells was noted with advancing age, and the frequency of epidermal CD49a+ CD8 TRM was increased in elderly individuals regardless of ethnicity. T-cell diversity and antipathogen responses were maintained in the skin of elderly individuals but declined in the blood. Our findings demonstrate that in elderly individuals, skin T cells maintain their density, diversity, and protective cytokine production despite the reduced T-cell diversity and function in blood. Skin resident T cells may represent a long-lived, highly protective reservoir of immunity in elderly people.