Expected results We will characterize target antigens of autoantibodies of patients with non-idiopathic and non SSc-associated PAH. We will compare these target to those previously identified in idiopathic or SSc-associated PAH. We will then, distinguish subpopulations of PAH patients whose serum or purified IgG (possibly specific for a given antigen) are able to induce ROS production or cell proliferation. For the population of ROS-producer patients, we will correlate the clinical response to vasodilatator therapy to results of in VITRO inhibition experiments with vasodilatators and anti-oxidant molecules.