A Sensitive Radioimmunoprecipitation Assay for the Detection of Antibody to Recombinant Human Gamma-interferon: Comparison to a Bioassay Neutralization Test

This report describes a specific radioimmunoprecipitation (RIP) assay for the detection of antibodies to recombinant DNA (rDNA) derived human gamma-interferon (rHuIFN-gamma). The assay was shown not to detect antibodies to rHuIFN-alpha, rHuIFN-beta, human lymphotoxin, or E. coli proteins and was reproducible with intraassay and interassay coefficients of variation of 1.6 and 3%, respectively, for the log titer of a high positive control. Comparison of this assay with a standard bioassay for detection of neutralizing antibody (abrogation of the inhibitory effect of rHuIFN-gamma on EMC virus replication in A549 cells) demonstrated that the RIP assay was more sensitive for detection of HuIFN-gamma neutralizing monoclonal antibody. Nonneutralizing monoclonal antibody was detectable in the RIP assay but not in the bioassay neutralization test. Examination of polyclonal antisera (rabbit and monkey) that contained neutralizing antibodies also demonstrated the RIP system to be a more sensitive indicator of the presence of antibodies than the bioassay neutralization test. In preliminary studies of human samples (86 patients) from clinical trials using an assay precipitation system capable of detecting antibody of the IgG, IgM, IgA, and IgE classes, no antibody to rHuIFN-gamma was observed. These patients were also found negative for neutralizing antibody to rHuIFN-gamma.