Abstract 16528: Activation of Classical Complement Pathway is Associated with the Development of Idiopathic Pulmonary Arterial Hypertension (IPAH)
Background: Circulating autoantibodies and activation of the complement system were reported in patients with IPAH. However target antigens isolated from lung tissue of IPAH patients have not been identified. We hypothesized that deposition of immune complexes (ICs) activates the classical complement pathway, and that targeting vascular antigens could be involved in the pathology of IPAH.
Methods: All experiments were done with age-matched lung tissue or plasma from IPAH patients and controls. Complement 3d (C3d) deposition in pulmonary arteries (PAs) was assessed by immunohistochemistry (blind scoring 0-3, none-intense). ELISA of lung lysates and plasma was used to detect binding of ICs and Complement 1q (C1q). Target lung tissue antigens were captured by immunoprecipitation (IP) with C1q or C1q antibody. The reactive bands were isolated following SDS-PAGE and Coomassie staining, and identified by Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS).
Results: We observed increased C3d deposition in lung tissue of IPAH patients (n=11) vs. controls (n=10): The % of PAs with moderate to intense staining was 73.3% ± 9.0% vs. 24.3% ± 9.3%, P=0.001. There was a significant correlation between C3d deposition and C1q binding in lung tissue (R2=0.30, P=0.01, n=18). No differences in C1q binding measured in plasma from IPAH patients (n=19) vs. controls (n=7) were noted, but in the lung values tended to be higher in the IPAH patients (n=27) vs. controls (n=14) (O.D./ total protein concentration mg/ml: 0.17± 02 vs. 0.12±0.1) with 4 considerably higher values. LC-MS/MS with C1q or C1q antibody identified 8 antigens of interest in 3 IPAH patients with high IC formation: myosin, actin, ezrin, clathrin, proteasome activator complex, peroxiredoxin-5, cyclophilin B, SAM domain and HD-containing protein 1.
Conclusions: Our data suggest greater activation of the classical complement pathway by local deposition of immune complexes in IPAH patients. The target antigens are related to the cytoskeleton, anti-inflammatory, anti-viral and antioxidant activity, suggesting that a subset of IPAH could be due to development of autoimmune responses against these proteins. Antibody-mediated subversion of these proteins could impair the vascular response to injury.
- © 2012 by American Heart Association, Inc.