Anti-endothelial cell antibodies (AECAs) were more prevalent in MCTD-PAH patients, and higher serum levels of thrombomodulin and von Willebrand factor antigen (vWFAg) were observed in these patients, with significant correlations between AECA quantity and both thrombomodulin and vWFAg levels. Here, THBD is linked to mixed connective tissue disease.