CD93 and systemic sclerosis: There are several serum markers previously reported to be correlated with skin fibrosis in SSc such as IL-6, IL-10, B cell-activating factor, IL-33, connective tissue growth factors, TGF-β, soluble tumor necrosis factor alpha (TNF-α)-receptor type 1, CC chemokine ligand 2, CXC chemokine ligand 4, a disintegrin and metalloprotease 12, soluble form of CD93, and soluble inducible costimulator21,25–33.