By using confocal laser scanning microscopy (LSM), we found that 20 of 23 SSc skin biopsies analyzed (86.9%) expressed CXCL4 in the dermis, whereas all HD skin biopsies (N = 11) were virtually negative for CXCL4 expression (Supplementary Fig. 1c). The gene discussed is PF4; the disease is systemic sclerosis.