Peripheral tolerance by Treg via constraining OX40 signal in autoreactive T cells against desmoglein 3, a target antigen in pemphigus.

Abstract

Antigen-specific peripheral tolerance is crucial to prevent the development of organ-specific autoimmunity. However, its function decoupled from thymic tolerance remains unclear. We used desmoglein 3 (Dsg3), a pemphigus antigen expressed in keratinocytes, to analyze peripheral tolerance under physiological antigen-expression conditions. Dsg3-deficient thymi were transplanted into athymic mice to create a unique condition in which Dsg3 was expressed only in peripheral tissue but not in the thymus. When bone marrow transfer was conducted from high-avidity Dsg3-specific T cell receptor-transgenic mice to thymus-transplanted mice, Dsg3-specific CD4⁺ T cells developed in the transplanted thymus but subsequently disappeared in the periphery. Additionally, when Dsg3-specific T cells developed in <i>Dsg3</i>^-/- mice were adoptively transferred into Dsg3-sufficient recipients, the T cells disappeared in an antigen-specific manner without inducing autoimmune dermatitis. However, Dsg3-specific T cells overcame this disappearance and thus induced autoimmune dermatitis in Treg-ablated recipients but not in <i>Foxp3</i>-mutant recipients with dysfunctional Tregs. The molecules involved in disappearance were sought by screening the transcriptomes of wild-type and <i>Foxp3</i>-mutant Tregs. <i>OX40</i> of Tregs was suggested to be responsible. Consistently, when <i>OX40</i> expression of Tregs was constrained, Dsg3-specific T cells did not disappear. Furthermore, Tregs obtained OX40L from dendritic cells in an <i>OX40</i>-dependent manner in vitro and then suppressed OX40L expression in dendritic cells and Birc5 expression in Dsg3-specific T cells in vivo. Lastly, CRISPR/Cas9-mediated knockout of <i>OX40</i> signaling in Dsg3-specific T cells restored their disappearance in Treg-ablated recipients. Thus, Treg-mediated peripheral deletion of autoreactive T cells operates as an <i>OX40</i>-dependent regulatory mechanism to avoid undesired autoimmunity besides thymic tolerance.