Solid-phase radioimmunoassay determination of virus-specific IgM antibody levels in a follow-up patients with naturally acquired measles infections.

The question of the exact disappearance time or possible persistence of measles-specific IgM antibodies after naturally acquired measles virus infections was studied with a sensitive solid-phase radioimmunoassay (RIA) method. A total of 30 patients were analyzed with follow-up times varying from 4.5 to 8 months; all were measles IgM positive in the first serum specimen obtained after the onset of rash. In 29 of 30 patients, the measles IgM declined to undetectable levels by approximately 90 days. The remaining patient developed postmeasles encephalitis, however, and was found to have a prolonged measles IgM antibody response. For comparison, the measles-specific IgG response was also studied and was found to develop only slightly later than the IgM response, with levels then remaining high and stable up to 8 months later. Although apparent measles IgM antibodies were found in 1 of 64 nonmatched adult controls, they were due to the presence of high levels of IgM-class rheumatoid factor. The data presented indicate that measles IgM antibodies begin to decline soon after the onset of rash and reach negative levels 1 to 3 months later; in complicated infections, however, measles IgM antibody synthesis may not terminate normally.