Simultaneous detection of allotypes in native and activated human C2 by isoelectric focusing and silver staining

A simple and highly sensitive analytical isoelectric focusing (IEF) technique using immunofixation with anti-C2 serum followed by silver staining has been developed in order to study simultaneously the structural polymorphism of both native C2 and C2 activation fragments (C2a MW 74,000 and C2b MW 34,000). Structural C2 polymorphism of C2*B and C2*C allotypes (but not of C2*A1) was found to be associated with the C2a fragment, whereas C2b appears to display no polymorphism. Commercially available IEF gels and C2 antisera gave reproducible allotyping data and make this technique of general use for densitometric analysis of native and activated C2. In vivo C2 activation was studied through C2a/native C2 area ratios obtained by computerized densitometry. Significantly lower ratios were observed in healthy individuals than in patients with systemic lupus erythematosus (SLE), reflecting an abnormally high classical pathway activation of complement in SLE. This methodology may be of value for immunogenetic and functional studies of other complement components.