Deletion of Foxp3⁺ regulatory T cells in genetically targeted mice supports development of intestinal inflammation

Mice lacking Foxp3⁺ regulatory T (Treg) cells develop severe tissue inflammation in lung, skin, and liver with premature death, whereas the intestine remains uninflamed. This study aims to demonstrate the importance of Foxp3⁺ Treg for the activation of T cells and the development of intestinal inflammation.

Foxp3-GFP-DTR (human diphtheria toxin receptor) C57BL/6 mice allow elimination of Foxp3⁺ Treg by treatment with Dx (diphtheria toxin). The influence of Foxp3⁺ Treg on intestinal inflammation was tested using the CD4⁺ T-cell transfer colitis model in Rag^−/− C57BL/6 mice and the acute DSS-colitis model.

Continuous depletion of Foxp3⁺ Treg in Foxp3-GFP-DTR mice led to dramatic weight loss and death of mice by day 28. After 10 days of depletion of Foxp3⁺ Treg, isolated CD4⁺ T-cells were activated and produced extensive amounts of IFN-γ, IL-13, and IL-17A. Transfer of total CD4⁺ T-cells isolated from Foxp3-GFP-DTR mice did not result in any changes of intestinal homeostasis in Rag^−/− C57BL/6 mice. However, administration of DTx between days 14 and 18 after T-cell reconstitution, lead to elimination of Foxp3⁺ Treg and to immediate weight loss due to intestinal inflammation. This pro-inflammatory effect of Foxp3⁺ Treg depletion consecutively increased inflammatory cytokine production. Further, the depletion of Foxp3⁺ Treg from Foxp3-GFP-DTR mice increased the severity of acute dSS-colitis accompanied by 80% lethality of Treg-depleted mice. CD4⁺ effector T-cells from Foxp3⁺ Treg-depleted mice produced significantly more pro-inflammatory cytokines.

Intermittent depletion of Foxp3⁺ Treg aggravates intestinal inflammatory responses demonstrating the importance of Foxp3⁺ Treg for the balance at the mucosal surface of the intestine.