Human small intestine contains 2 functionally distinct regulatory T-cell subsets

Regulatory T (Treg) CD4 cells in mouse gut are mainly specific for intestinal antigens and play an important role in the suppression of immune responses against harmless dietary antigens and members of the microbiota. However, information about the phenotype and function of Treg cells in the human gut is limited.

We performed a detailed characterization of Foxp3⁺ CD4 Treg cells in human normal small intestine (SI) as well as from transplanted duodenum and celiac disease lesions.

Treg cells and conventional CD4 T cells derived from SI were subjected to extensive immunophenotyping and their suppressive activity and ability to produce cytokines assessed.

SI Foxp3⁺ CD4 T cells were CD45RA^-CD127^-CTLA-4⁺ and suppressed proliferation of autologous T cells. Approximately 60% of Treg cells expressed the transcription factor Helios. When stimulated, Helios-negative Treg cells produced IL-17, IFN-γ, and IL-10, whereas Helios-positive Treg cells produced very low levels of these cytokines. By sampling mucosal tissue from transplanted human duodenum, we demonstrated that donor Helios-negative Treg cells persisted for at least 1 year after transplantation. In normal SI, Foxp3⁺ Treg cells constituted only 2% of all CD4 T cells, while in active celiac disease, both Helios-negative and Helios-positive subsets expanded 5- to 10-fold.

The SI contains 2 subsets of Treg cells with different phenotypes and functional capacities. Both subsets are scarce in healthy gut but increase dramatically in active celiac disease.