Background

IL-10 is an anti-inflammatory cytokine required for intestinal immune homeostasis. It mediates suppression of T-cell responses by type 1 regulatory T (T_R1) cells but is also produced by CD25⁺ regulatory T (Treg) cells.

Objective

We aimed to identify and characterize human intestinal T_R1 cells and to investigate whether they are a relevant cellular source of IL-10 in patients with inflammatory bowel diseases (IBDs).

Methods

CD4⁺ T cells isolated from the intestinal lamina propria of human subjects and mice were analyzed for phenotype, cytokine production, and suppressive capacities. Intracellular IL-10 expression by CD4⁺ T-cell subsets in the inflamed guts of patients with IBD (Crohn disease or ulcerative colitis) was compared with that in cells from noninflamed control subjects. Finally, the effects of proinflammatory cytokines on T-cell IL-10 expression were analyzed, and IL-1β and IL-23 responsiveness was assessed.

Results

Intestinal T_R1 cells could be identified by coexpression of CCR5 and programmed cell death protein 1 (PD-1) in human subjects and mice. CCR5⁺PD-1⁺ T_R1 cells expressed IFN-γ and efficiently suppressed T-cell proliferation and transfer colitis. Intestinal IFN-γ⁺ T_R1 cells, but not IL-7 receptor–positive T_H cells or CD25⁺ Treg cells, showed lower IL-10 expression in patients with IBDs. T_R1 cells were responsive to IL-23, and IFN-γ⁺ T_R1 cells downregulated IL-10 with IL-1β and IL-23. Conversely, CD25⁺ Treg cells expressed higher levels of IL-1 receptor but showed stable IL-10 expression.

Conclusions

We provide the first ex vivo characterization of human intestinal T_R1 cells. Selective downregulation of IL-10 by IFN-γ⁺ T_R1 cells in response to proinflammatory cytokines is likely to drive excessive intestinal inflammation in patients with IBDs.