Tanned-cell hemagglutination test for detection of antibodies in sera of patients with myasthenia gravis

Previous studies revealed the presence of 2 types of autoantibodies in the sera of some patients suffering from myasthenia gravis, one reactive with both skeletal muscle and heart and the other with skeletal muscle only. The observations were based on studies of direct, indirect, and complement immunofluorescent staining and on conventional complement fixation tests. This article deals with the demonstration of muscle antibodies by the tanned-cell hemagglutination technique. Sera of some patients gave positive reactions in dilutions as high as 1:65,000, with cells coated at pH 6.4 by a fraction of muscle precipitated between 1 and 1.6M ammonium sulfate. Both skeletal and heart muscle preparations served as coating antigens under appropriate conditions; cells coated with smooth muscle antigen failed to react. These observations suggest that SH (skeletal and heart) antibodies are operative in the tanned-cell hemagglutination test. Tanned red cells coated with fractions prepared from muscle of each of 2 antibody-producing patients reacted with the patient's own sera, pointing to the autoantibody nature of the reactions. Comparative tests were performed with sera from 45 patients with myasthenia gravis by tanned-cell hemagglutination, immunofluorescent staining, and complement fixation; 14 were considered positive. Of the 45 sera, 10 yielded positive tanned-cell tests with human muscle fractions, 8 yielded positive immunofluorescent staining of muscle striations, and 6 yielded positive complement fixation with muscle extracts. None of the 58 control sera tested yielded unequivocally positive reactions. Thus, the hemagglutination reaction is at least as sensitive and specific as immunofluorescent staining in the detection of SH antibodies in sera of patients with myasthenia gravis.