The immunological characteristics of IgG4-RD and SSc overlap, where CD4+ T cells—including the unusual subpopulation of IFN-γ, IL-1β, and TGF-β secreting cytotoxic CD4+ T cells (CTLs)—play a key role in disease pathogenesis [4, 15]. Here, CD4 is linked to immunoglobulin G4-related sclerosing disease.