An M-antibody capture radioimmunoassay (MACRIA) for detection of JC virus-specific IgM

A solid-phase M-antibody capture radioimmunoassay (MACRIA) for detecting JC-specific IgM is described. The assay is based on a JC-specific monoclonal antibody (17.7.6) and Nonidet P40-treated, glycine-extracted antigen. MACRIA is more sensitive for JC IgM detection than haemagglutination inhibition (HI) following serum fractionation on a sucrose density gradient, and can be applied to large numbers of sera. The specificity of the assay was confirmed by examining sera from several acute virus infections and also those containing rheumatoid factor. Sera collected from renal transplant recipients with known active JC virus infection were found to contain more than 5 units of JC IgM. In this group of patients JC IgM represents either primary or reactivated JC infection. JC IgM was detected by MACRIA in 15 of 100 unselected blood donors, indicating that JC IgM is frequently produced in healthy seropositive individuals. Thirteen of the 15 sera positive from blood donors contained only low levels of JC IgM (< 5 units), but the specificity of all these results was confirmed in a blocking assay. It is suggested that these low levels of JC IgM may occur in up to 28% of seropositive individuals and result from active JC antigenic stimulation in healthy immunocompetent adults.