Anti-fibroblast and anti-endothelial cell autoantibodies in pulmonary arterial hypertension (PAH) in patients with connective tissue diseases (CTD)

Objectives Pulmonary arterial hypertension (PAH) is a rare disease that may be associated with connective tissue diseases (CTD). Anti-fibroblast (AFA) and anti-endothelial cell autoantibodies (AECA) have been identified in idiopathic and systemic sclerosis (SSc)-associated PAH. The aim was to identify autoantibodies discriminating for PAH associated with systemic lupus erythematosus (SLE), mixed connective tissue disease (MCTD) and primary Sjögren's syndrome (SS), and their target antigens. Methods Sera were collected in the French multicentre Auto-HTAP study from 86 patients with CTD excluding SSc, including 32 with PAH (PAH+) and 54 without (PAH–). AFA and AECA were identified using one (1D) and two dimensions (2D) immunoblots and proteomics. ELISA tests using human recombinant proteins were used to confirm PAH-associated IgG reactivities. Results PAH+ patients had similar IgG AFA and AECA reactivities in 56.2% and 40.6% of the cases in 1D immunoblots, respectively. In 2D immunoblots, serum IgG pools from SLE patients (n = 14), MCTD (n = 10), SS (n = 9) and 14 healthy controls (n = 1) recognized respectively 273 ± 79, 205 ± 77, 109 ± 11 and 109 protein spots in fibroblasts and 189 ± 48, 146 ± 30, 88 ± 33 and 190 protein spots in endothelial cell extracts. Serum IgG from PAH+ patients recognized 39 fibroblast and 34 endothelial cell protein spots that were not recognized by IgG from PAH– patients, including Annexin A5 (ANXA5). Anti-ANXA5 IgG reactivity was significantly higher in PAH+ compared with PAH– patients with MCTD (73% vs 0%, p< 0.001) and SLE (33% vs 0%, p= 0.009). Conclusion Anti-ANXA5 IgG autoantibody reactivity might represent a predictive biomarker for PAH associated with MCTD and SLE.