Detection of the genetic polymorphism of human C2 (native protein and C2a fragment) by immunoblotting after polyacrylamide gel isoelectric focusing.

The polymorphism of the second component of human complement (C2) was studied by means of isoelectric focusing in polyacrylamide gels followed by immunoblotting with a specific antihuman C2 antibody. The polymorphism was studied in native C2 and in the C2a fragment obtained by activation of the classical pathway with heat-aggregated human IgG. Serum samples previously typed with the hemolytic overlay technique were analyzed. They comprised samples of homozygous C2C, C2B, C2Q0, heterozygous C2BC and C2CQ0 individuals. The patterns obtained by immunoblotting corresponded to those obtained by the hemolytic overlay technique. As expected, the homozygous C2Q0 sample (complement C2 deficiency) did not show any band pattern. The C2a fragment presented also a polymorphic variation which correlated exactly with the native C2 polymorphism. It appears thus that the polymorphic site of the C2 protein is carried by the C2a fragment for the C2C and C2B variants. In addition, this method is easier to perform than the common hemolytic overlay technique and the rare C2-deficient serum is not needed.