Evaluation of a radioimmunoassay for IgM-class antibodies against cytomegalovirus.

A solid-phase radioimmunoassay (RIA-IgM) test for cytomegalovirus (CMV)-specific IgM-class antibodies is described and its potential diagnostic usefulness in adult patients is evaluated. IgM-class antibodies were readily detected by RIA in early convalescent sera from patients with serologically confirmed primary CMV infection, as well as in sera from patients with CMV mononucleosis. Serum specimens obtained several months after primary infection gave either negative results of low antibody titres, indicating that the IgM response is transient in these patients. CMV-specific IgM was also detected in 7 of 10 patients with symptoms and supportive serological evidence suggestive of recent active CMV infection. Conversely, 12 patients who were thought not to have experienced recent primary CMV infection, but whose sera gave high complement-fixing (CF) antibody titres, and 14 of 15 renal transplant recipients with reactivated CMV gave negative results in the RIA-IgM test. The results indicate that detectable IgM antibody production is a constant feature in patients with primary infection but not in patients who experience mild secondary attacks. The RIA-IgM test is highly virus-specific and can reliably be performed with unfractionated serum, provided that false reactivity due to rheumatoid factor (RF) is excluded. Thus RIA is a simple and specific technique which could be usefully applied as a diagnostic tool in a clinical situation and in research.