Regulatory T cells suppress autoreactive CD4+ T cell response to bladder epithelial antigen

AIM: To investigate the role of regulatory T (Treg) cells in CD4⁺ T cell-mediated bladder autoimmune inflammation.METHODS: Urothelium-ovalbumin (URO-OVA)/OT-II mice, a double transgenic line that expresses the membrane form of the model antigen (Ag) OVA as a self-Ag on the urothelium and the OVA-specific CD4⁺ T cell receptor specific for the I-A^b/OVA_323-339 epitope in the periphery, were developed to provide an autoimmune environment for investigation of the role of Treg cells in bladder autoimmune inflammation. To facilitate Treg cell analysis, we further developed URO-OVA^GFP-Foxp3/OT-II mice, a derived line of URO-OVA/OT-II mice that express the green fluorescent protein (GFP)-forkhead box protein P3 (Foxp3) fusion protein.RESULTS: URO-OVA/OT-II mice failed to develop bladder inflammation despite the presence of autoreactive CD4⁺ T cells. By monitoring GFP-positive cells, bladder infiltration of CD4⁺ Treg cells was observed in URO-OVA^GFP-Foxp3/OT-II mice. The infiltrating Treg cells were functionally active and expressed Treg cell effector molecule as well as marker mRNAs including transforming growth factor-β, interleukin (IL)-10, fibrinogen-like protein 2, and glucocorticoid-induced tumor necrosis factor receptor (GITR). Studies further revealed that Treg cells from URO-OVA^GFP-Foxp3/OT-II mice were suppressive and inhibited autoreactive CD4⁺ T cell proliferation and interferon (IFN)-γ production in response to OVA Ag stimulation. Depletion of GITR-positive cells led to spontaneous development of bladder inflammation and expression of inflammatory factor mRNAs for IFN-γ, IL-6, tumor necrosis factor-α and nerve growth factor in URO-OVA^GFP-Foxp3/OT-II mice.CONCLUSION: Treg cells specific for bladder epithelial Ag play an important role in immunological homeostasis and the control of CD4⁺ T cell-mediated bladder autoimmune inflammation.