DEF6 and systemic lupus erythematosus: • guanine nucleotide exchange factor for small GTPases highly expressed in T cells• involved in TCR induced cytoskeleton reorganization and Ca2+/NFAT signaling• deficiency causes impaired T cell function and a lupus-like symptoms• combined deficiency of Def6 and the related SWAP-70 results in eTreg expansion• can directly interact with IRF4 and restrict its binding to subsets of target genes→ enhanced accessibility could further restrict IRF4 function in Treg cells