A simple and rapid method for detection of serum IgM antibodies to the rubella virus hemagglutinin

Serum IgM antibodies directed against the rubella virus hemagglutinin can be detected without prior serum fractionation. In the first step of a newly developed method, chick erythrocytes were sensitized with a subhemagglutinating dose of rubella hemagglutinin. Next, the sensitized erythrocytes were mixed with patient serum, allowing specific antibodies to react with the fixed antigens. Finally, rabbit antibodies to human IgM were used to create bridges between IgM molecules on different blood cells. The visible result was an easily read hemagglutination with sera which contain specific rubella IgM antibodies. The procedure is very simple and rapid to perform. At least 20 sera can be examined in approximately 2 h. No sophisticated instruments are needed. We have tentatively called the new method rubella anti-IgM hemagglutination (HA). Rubella anti-IgM HA was more sensitive than the standard density gradient centrifugation/hemagglutination inhibition technique, but the correlation between the methods was good. Non-specific inhibitors of hemagglutination or rheumatoid factors did not seem to interfere with the specificity of the new method, and competition for antigenic sites between antibodies from the IgG/IgA and IgM classes did not seem to represent a serious, practical problem.