Immunoradiometric assay for cytomegalovirus-specific IgG antibodies: assay development and evaluation in blood transfusion practice

An immunoradiometric assay (radio-immunosorbent test; RIST) for the detection of IgG antibodies to human herpesvirus 4 [human cytomegalovirus (CMV)] has been developed. The technique utilizes CMV antigen passively adsorbed to a polyvinyl microtitration plate and a radiolabelled murine monoclonal anti-human IgG antibody to detect binding of human antibody to the 'solid phase' reagent. The assay was optimized, and its specificity confirmed by testing paired acute and convalescent sera from patients with acute CMV or other human herpesvirus infections. To determine the assay's sensitivity 1433 blood donor sera were examined. The RIST was more sensitive than a standard complement fixation (CFT), in that 53% of these sera were positive by RIST and 48% positive by CFT. There were 1303 concordant results, 88 sera positive only by RIST and 19 sera were only positive by CFT. These discrepant results remained after an attempt to exclude false positive reactivity; their significance is discussed. Use of a monoclonal anti-human IgG antibody in the RIST reduced non-specific binding to the control uninfected cell antigen such that blood donor sera could be tested in the assay using only a CMV antigen without generating an unacceptable false positive rate.