Several strategies are being designed to test the therapeutic potential of Ag-specific regulatory T cells to prevent or treat autoimmune diseases. In this study, we demonstrate that naive CD4+Foxp3− T cells specific for a naturally expressed autoantigen (H+/K+ ATPase) can be converted to Foxp3+ T regulatory cells (Tregs) when stimulated in presence of TGFβ. TGFβ-induced Tregs (iTregs) have all the characteristics of naturally generated regulatory T cells in vitro, and more importantly, are effective at preventing organ-specific autoimmunity in a murine model of autoimmune gastritis. H+/K+ ATPase specific iTregs were able to inhibit the initial priming and proliferation of autoreactive T cells, and appear to do so by acting on H+/K+ ATPase presenting dendritic cells (DC). DC exposed to iTregs in vivo were reduced in their ability to stimulate proliferation and cytokine production by H+/K+ ATPase specific T cells. iTregs specifically reduced CD80 and CD86 expression on the surface of H+/K+ ATPase presenting DC in vitro. These studies reveal the therapeutic potential of Ag specific iTregs to prevent autoimmunity, and provide a mechanism by which this population of regulatory T cells, and perhaps others, mediate their suppressive effects in vivo.

T regulatory cells (T regs ) can activate multiple suppressive mechanisms in vitro upon activation via the T cell receptor resulting in antigen-independent suppression. However, it remains unclear whether similar pathways operate in vivo. Here, we found that antigen-specific T regs activated by dendritic cells (DCs) pulsed with two antigens suppressed T naive specific for both cognate and non-cognate antigens in vitro, but only suppressed T naive specific for cognate antigen in vivo. Antigen-specific T regs formed strong interactions with DC resulting in selective inhibition of the binding of T naive to cognate antigen, yet allowing bystander T naive access. Strong binding resulted in removal of the cognate peptide-MHCII (pMHCII) from the DC surface reducing the capacity of the DC to present antigen. The enhanced binding of T regs to DC coupled with their capacity to deplete pMHCII represents a novel pathway for T reg -mediated suppression and may be a mechanism by which T regs maintain immune homeostasis.

Th cells can be subdivided into IFN-γ-secreting Th1, IL-4/IL-5-secreting Th2, and IL-17-secreting Th17 cells. We have evaluated the capacity of fully differentiated Th1, Th2, and Th17 cells derived from a mouse bearing a transgenic TCR specific for the gastric parietal cell antigen, H+K+-ATPase, to induce autoimmune gastritis after transfer to immunodeficient recipients. We have also determined the susceptibility of the disease induced by each of the effector T cell types to suppression by polyclonal regulatory T cells (Treg) in vivo. Each type of effector cell induced autoimmune gastritis with distinct histological patterns. Th17 cells induced the most destructive disease with cellular infiltrates composed primarily of eosinophils accompanied by high levels of serum IgE. Polyclonal Treg could suppress the capacity of Th1 cells, could moderately suppress Th2 cells, but could suppress Th17-induced disease only at early time points. The major effect of the Treg was to inhibit the expansion of the effector T cells. However, effector cells isolated from protected animals were not anergic and were fully competent to proliferate and produce effector cytokines ex vivo. The strong inhibitory effect of polyclonal Treg on the capacity of some types of differentiated effector cells to induce disease provides an experimental basis for the clinical use of polyclonal Treg in the treatment of autoimmune disease in humans.