Foxp3 domain-swap interface is required to suppress T helper type 2 transcriptional program in Regulatory T cells.

Abstract

Abstract Regulatory T cells (Treg) play a fundamental role in maintaining immune tolerance. These cells are defined and characterized by expression of the master regulator Foxp3, a transcription factor that is crucial for Treg function and homeostasis. Natural occurring mutations in Foxp3 gene have been shown to be responsible for the immunodysregulation polyendocrinopathy enteropathy X-linked (IPEX) syndrome, which is characterized by widespread autoimmune diseases. We recently identified a Foxp3 mutation in a boy that manifested a severe IPEX syndrome. This mutation, resulting in the substitution of methionine for isoleucine at amino acid 370 was determined to be part of a class of Foxp3 mutations that disrupt the dimerization motif in the domain swap interface of the protein. We have shown that, although dimerization mutants retain DNA binding, allows Treg development and certain Treg characteristics, it inevitably led to an IPEX syndrome in humans and mice. Genomic analysis of M370I mutant Treg by RNAseq, ChIPseq and HiChIP revealed a de-repression of the T helper type 2 (Th2) transcriptional program leading to the generation of Th2-like Treg. We have shown that, dimerization mutant proteins bind to multiple locations in the Th2 locus leading to increased intrachromosomal interactions and Th2 cytokines production. As expected, M370I Tregs were unable to suppress Th2 immune responses. Transgenic mice expressing M370I Foxp3 developed autoimmune diseases characterized by systemic Th2 cytokines production and skin and lung inflammation. In conclusion, disruption of the domain swap interface of Foxp3 by M370I mutation led to the development of Th2-like Treg which are functionally unable to suppress the development/function of Th2 cells.