The striking differences in SRC binding by reduced versus oxidized PTP4A1 and the high specificity of our PLA assay therefore point to a strong induction of an oxo-PTP4A1-SRC complex in fibrotic skin from patients with SSc and mouse models of disease as well as in ex vivo cultured dermal fibroblasts subjected to TGF-β stimulation. The gene discussed is PTP4A1; the disease is systemic sclerosis.