GP9 and pulmonary arterial hypertension: HLA-DR showed higher expression in PAH patients with respect to ILD patients (p = 0.02), CD25 showed higher expression in PAH patients with respect uncomplicated SSc (p = 0.02), and CD42a showed higher expression in PAH patients with respect to the controls (p = 0.03); nevertheless, multivariate analyses demonstrated that only CD3 retained its association with PAH.