Use of monoclonal antibodies to quantify subclasses of human IgG: II. Enzyme immunoassay to define antigen specific (anti-filarial) IgG subclass antibodies

Because of their single epitope specificity, monoclonal antibodies (Mcabs) may perform with different levels of efficiency in immunoassays depending on the accessiblity of the particular epitope recognized. In order to develop assays capable of detecting specific antibodies of each of the four human IgG subclasses, we have evaluated by ELISA the performance characteristics of a panel of Mcabs raised to the subclass proteins. At least one Mcab to each of the four subclasses was identified that was specific in its ability to capture its own relevant IgG subclass without any associated light chain, allotype or isoallotype activity and that was able to function effectively as a probe in an optimized, quantitative ELISA. When IgG subclass antibodies were measured in sera from patients with filariasis using specific filarial antigen, the sensitivities of each subclass antibody assay varied; for IgG1 and IgG4 antibodies the sensitivity of detection was 50 ng/ml and for IgG2 and IgG3, 10 ng/ml. The potency of the Mcab, determined by its titration for use as a probe, did not correlate with the sensitivity of the assay. These Mcabs were also capable of defining IgG subclass antibody responses qualitatively in immunoblot analyses with little or no non-specific binding. The availability of such highly characterized Mcabs for use in quantitative and qualitative definition of specific IgG subclass antibody responses should greatly improve our detection and subsequent understanding of the role of these IgG subclasses in various disease states.