Immunoglobulin responses after rubella infection.

The indirect immunofluorescence technique has been used to study specific IgG, IgA, and IgM antibodies in adults with acute rubella, volunteers who receive attentuated rubella vaccine, and infants with suspected congenital infection. In acute rubella, IgA and IgM antibodies reached peak titers during the second week after the rash and then declined, but specific IgG persisted. A similar pattern of response occurred after rubella vaccination, but titers were lower. Occasionally, fluorescent staining failed to detect specific IgM in whole serum but demonstrated it clearly in sucrose density gradient fractions. The improvement in fluorescence obtained by staining serum fractions was particularly striking in samples obtained from congenitally infected infants. In these cases, IgM staining with whole serum was often poor, but when fractions were tested, specific IgM was demonstrated in nearly all samples obtained within 9 months of birth. IgM antibody was seldom detected after the first year of life, but IgG antibody persisted. IgA antibody was not detected in congenital rubella.