A novel immunoassay for the quantitation of human C4 gene products

Utilizing mouse monoclonal antibodies which recognize Rodgers 1 and Chido 1 epitopes carried on the C4A and C4B molecules, and heat-aggregated IgG to activate C1, an immunoassay was developed for the quantitation of total C4 as well as C4A and C4B. Interassay variation was 12.4, 11.5 and 10.8%, respectively. The immunoassay was compared to the quantitation of total C4 by radial immunodiffusion by testing 103 random white controls and gave a Pearson's product-moment correlation coefficient of 0.81. Three genetic total-C4-deficient individuals were nonreactive in all three assays. This activated assay is specific, reproducible, and superior to existing methods for the quantitation of C4A and C4B and detection of the heterozygous C4 null state.