Objective To investigate the prevalence of anti-endothelial cell antibodies (AECAs) in the sera of connective tissue diseases (CTD) patients with pulmonary arterial hypertension (PAH) and its correlation with clinical manifestations. Methods AECAs in sera of 39 CTD patients with PAH

22 CTD patients without PAH

and 10 healthy donors as controls were detected with Western blotting. The prevalence of different AECAs in different groups was compared and its correlation with clinical manifestations was also investigated. Results The prevalence of AECAs was 82.1% in CTD patients with PAH

72.7% in CTD patients without PAH

and 20.0% in healthy donors. Anti-22 kD AECA was only detected in CTD patients with PAH (15.4%). Anti-75 kD AECA was more frequently detected in CTD patients with PAH than in those without PAH (51.3% vs. 22.7%

P<0.05). In CTD patients with PAH

anti-75 kD AECA was more frequently detected in those with Raynaud’s phenomenon or with positive anti-RNP antibody. Conclusion AEC As could be frequently detected in CTD patients with or without PAH

while anti-22 kD and anti-75 kD AECA might be specific in CTD patients with PAH.