Rationale: Pulmonary arterial hypertension (PAH) may be classified as idiopathic (IPAH) or familial (FPAH) or associated with various conditions and exposures such as dexfenfluramine intake (Dex-PAH) or systemic sclerosis (SSc-PAH). Because fibroblast dysfunction has been identified in SSc and IPAH and antifibroblast antibodies (AFAs) with a pathogenic role have been detected in the serum of SSc patients, we used a proteomic approach combining two-dimensional electrophoresis and immunoblotting to identify the target antigens of AFAs in such patients.

Objectives: To identify target antigens of antifibroblast antibodies in pulmonary arterial hypertension.

Methods: Sera from 24 patients with IPAH, 6 with FPAH, 6 with Dex-PAH, and 12 with SSc-PAH were collected. We pooled sera from sets of three patients with PAH classification and SSc-PAH based on autoantibody profile. Sera from 14 healthy blood donors were also pooled and used as a control.

Measurements and main results: Serum IgG antibodies in the pools of patients with IPAH (n = 8), FPAH (n = 2), Dex-PAH (n = 2), and SSc-PAH (n = 4) recognized 103 +/- 31, 63 +/- 20, 78 +/- 11, and 81 +/- 12 protein spots, respectively, whereas serum IgG antibodies from healthy control subjects recognized 43 +/- 22 protein spots. Twenty-one protein spots were specifically recognized by the serum IgG antibodies from patients with PAH. We identified 16 of the protein spots as vimentin, calumenin, tropomyosin 1, heat shock proteins 27 and 70, glucose-6-phosphate-dehydrogenase, phosphatidylinositol 3-kinase, DAP kinase, and others. These proteins are involved in regulation of cytoskeletal function, cell contraction, oxidative stress, cell energy metabolism, and other key cellular pathways.

Conclusions: AFAs detected in patients with PAH recognize cellular targets playing key roles in cell biology and maintenance of homeostasis.