The C1q binding activity of IgG is modified in vitro by reactive oxygen species: implications for rheumatoid arthritis

Abstract

IgG can be denatured in vitro by reactive oxygen species (ROS). Native IgG activates the complement cascade through C1q. Using a modified ELISA, C1q binding activity of rheumatoid IgG has been compared to IgG denatured by neutrophil-derived ROS. The C1q binding activity of rheumatoid synovial fluid IgG is greater than the corresponding serum IgG ( P < 0.01). Denaturation of IgG by activated polymorphs or the Fenton reaction decreased its C1q binding activity ( P < 0.01). In vitro exposure of IgG to OH · and ROO · increased its interaction with C1q ( P < 0.01). Hypochlorous acid had no effect. ROS-induced alteration to IgG-C1q binding activity may promote the inflammatory response in rheumatoid arthritis.