Persistence of immunoglobulin G and immunoglobulin M antibodies after postnatal rubella infection determined by solid-phase radioimmunoassay

The appearance and persistence of immunoglobulin M (IgM) and IgG antibodies in postnatal rubella infections were studied by employing a solid-phase radioimmunoassay test. Altogether, 222 serial serum specimens from 51 patients with acute rubella infection were tested. Both IgG and IgM antibodies developed rapidly and appeared in all patients within 4 days after the onset of rash. In some patients, the IgM antibodies clearly preceded the IgG antibodies; however, the reverse situation was also noticed in a few cases. The IgG antibodies showed only minor changes after 8 to 10 days from the onset of rash. The IgM titers also reached a maximum level at approximately 8 to 10 days after the onset of rash, after which time a rapid decrease was normally seen. The mean half-life of IgM antibodies after 15 days from the onset of rash was 4.5 days, giving for IgM antibodies persistence times from 43 to approximately 80 days. Two patients with a prolonged IgM antibody response were detected. One of these patients had bilateral arthritis of the knee as a complication, whereas in the other patient no complication caused by rubella virus was detected. The IgM antibody response and its value in diagnosis are discussed.