The DEL-1–β3 integrin axis promotes Runx-1–dependent Foxp3 expression and regulatory T cell responses at mucosal barrier sites

Foxp3+CD4+ regulatory T cells (Tregs) are critical for immune homeostasis and respond to local tissue cues, which control their stability and function. We explored here whether DEL-1, which, like Tregs, increases during resolution of inflammation, promotes Treg responses. DEL-1 enhanced Treg numbers and function at barrier sites (oral and lung mucosa). The underlying mechanism was dissected using mice lacking DEL-1 or expressing a point mutant thereof, or mice with CD4-specific deletion of the transcription factor Runx1, identified by RNA-seq analysis of the DEL-1-induced Treg transcriptome. Specifically, through interaction with avβ3-integrin, DEL-1 promoted induction of Runx1-dependent Foxp3 expression and conferred stability of Foxp3 expression upon Treg restimulation in the absence of exogenous TGFβ1. Additionally, DEL-1 increased RUNX1 and FOXP3 expression in human conventional T cells promoting their conversion into induced Tregs with increased TSDR demethylation, increased stability and suppressive activity. We thus uncovered a DEL-1-avβ3-Runx1 axis that promotes Treg responses at barrier sites and offers novel therapeutic options for modulating inflammatory/autoimmune disorders. We examined gene expression by RNA-seq in Tregs treated with DEL-1-Fc or Fc control