STAT1 and systemic lupus erythematosus: Since the phosphorylation of STAT1 plays a key role in IFN-I signaling [23,56] and the increased gene expression of STAT1 has already been described in the PBMCs of SSc and SLE patients [32,57], we examined the phosphorylation of STAT1 in the B cells of dcSSc patients and HCs.