IgM antibodies in rubella infections: absorption with staphylococcal protein A of sera examined by immunofluorescence and haemagglutination inhibition.

A similar frequency of positive results for rubella IgM antibodies in the sera of rubella patients and persons contacting such patients was obtained by immunofluorescence after separation of IgM is sucrose gradient and after absorption of the sera with Staphylococcus aureus and immunoglobulin aggregates. Compared to the immunofluorescence method, the haemagglutination method for rubella IgM antibodies performed after absorption of the sera with S. aureus and reduction of immunoglobulins M with 2-mercaptoethanol was less sensitive for serum samples taken in the acute phase of the disease and 5 weeks after the appearance of rubella symptoms.