Common polymorphisms in C3, factor B, and factor H collaborate to determine systemic complement activity and disease risk

Proc Natl Acad Sci U S A. 2011 May 24;108(21):8761-6. doi: 10.1073/pnas.1019338108. Epub 2011 May 9.

Abstract

Common polymorphisms in complement alternative pathway (AP) proteins C3 (C3(R102G)), factor B (fB(R32Q)), and factor H (fH(V62I)) are associated with age-related macular degeneration (AMD) and other pathologies. Our published work showed that fB(R32Q) influences C3 convertase formation, whereas fH(V62I) affects factor I cofactor activity. Here we show how C3(R102G) (C3S/F) influences AP activity. In hemolysis assays, C3(102G) activated AP more efficiently (EC(50) C3(102G): 157 nM; C3(102R): 191 nM; P < 0.0001). fB binding kinetics and convertase stability were identical, but native and recombinant fH bound more strongly to C3b(102R) (K(D) C3b(102R): 1.0 μM; C3b(102G): 1.4 μM; P < 0.0001). Accelerated decay was unaltered, but fH cofactor activity was reduced for C3b(102G), favoring AP amplification. Combining disease "risk" variants (C3(102G), fB(32R), and fH(62V)) in add-back assays yielded sixfold higher hemolytic activity compared with "protective" variants (C3(102R), fB(32Q), and fH(62I); P < 0.0001). These data introduce the concept of a functional complotype (combination of polymorphisms) defining complement activity in an individual, thereby influencing susceptibility to AP-driven disease.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Complement Activation / genetics*
  • Complement C3 / genetics*
  • Complement C3-C5 Convertases / metabolism
  • Complement Factor B / genetics*
  • Complement Factor H / genetics*
  • Disease Susceptibility / immunology*
  • Fibrinogen / metabolism
  • Humans
  • Macular Degeneration
  • Polymorphism, Genetic / immunology*
  • Protein Binding
  • Risk Factors

Substances

  • C3 protein, human
  • Complement C3
  • Complement Factor H
  • Fibrinogen
  • Complement C3-C5 Convertases
  • Complement Factor B