[Rubella virus hemagglutination inhibition IgM antibodies: the method of absorption of IgG by staphylococcal protein A as compared with density gradient ultracentrifugation (author's transl)].

The elimination of IgG by adsorption to Protein A of S. aureus was used for the demonstration of rubella virus specific IgM by hemagglutination inhibition. The validity of the method was proved by comparison with the results of density gradient centrifugation. The adsorption procedure led to false positive results in 9 of 56 cases and to false negative results in 12 of 46 cases, i.e. 20.7% of the results were discordant, when the sera were tested with short incubation time (30 min. room temperature) and the residual IgG (and IgA) were not excluded by controls with 2-ME (table 1 and table 2). By prolonged incubation time (18 hrs + 4 degrees C) and controls with 2-ME, false positive results were avoided, and the number of false negative results was reduced to 9 (table 2 and table 3). The latter occured mostly in cases where the disease had started 3 or more weeks ago and the titer in the IgM fraction of the sera was low (fig. 3). Under these conditions the absorption of IgG by staphylococcal Protein A proved to be a simple, specific and reliable procedure for the demonstration of rubella virus IgM within 2-3 weeks after the onset of the disease.