RUBELLA-VIRUS HEMAGGLUTINATION INHIBITION IGM ANTIBODIES - METHOD OF ABSORPTION OF IGG BY STAPHYLOCOCCAL PROTEIN-A AS COMPARED WITH DENSITY GRADIENT ULTRACENTRIFUGATION

The elimination of IgG [immunoglobulin G] by adsorption to Protein A of Staphylococcus 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 [human] 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 [mercaptoethanol]. By prolonged incubation time (18 h at 4.degree. C) and controls with 2-ME, false positive results were avoided, and the number of false negative results was reduced to 9. The latter occured mostly in cases where the disease started .gtoreq. 3 wk earlier and the serum IgM titer was low. Under these conditions the absorption of IgG by staphylococcal Protein A was a simple, specific and reliable procedure for the demonstration of rubella virus IgM within 2-3 wk after the onset of the disease.