Serum IgM and IgG responses in postnatally acquired rubella.

Abstract Sucrose-density-gradient studies on sera from patients recently convalescent from rubella showed that specific IgM could be detected by haemagglutination-inhibition tests for up to 20 days from the onset of illness. This was associated with a significant increase in the concentrations of total IgM but not IgG, the IgM response being maximal 5-14 days after the onset of illness. After a month, only IgG could be detected. Complement-fixation antibodies, even when appearing early, consisted of IgG alone. Serum-total-IgG concentrations showed little variation in healthy patients throughout pregnancy, while IgM concentrations were reduced during the second trimester of pregnancy. The presence of a rubella-infected conceptus did not produce an unusually prolonged IgM response. Reduction in antibody titre in sera after treatment with 2-mercaptoethanol provided a less reliable method for demonstrating recent infection, since reductions in titre were associated usually with significantly raised total-IgM levels.