Identification of Mycobacterium tuberculosis antigens in Seibert fractions by immunoblotting

Seibert fractions prepared from Mycobacterium tuberculosis culture filtrates were evaluated by immunoblotting with a serum pool from patients with active pulmonary tuberculosis. Antibody activity was observed primarily with antigens in the polysaccharide II and A protein fractions; these fractions were further evaluated by immunoblotting with sera from individual patients with tuberculosis, from individuals without tuberculosis and positive for the purified protein derivative antigen skin test, and from individuals negative for the purified protein derivative antigen skin test. The antigens identified in the protein A fraction, a 32,000-molecular-weight antigen and a heterogeneous high-molecular-weight antigen, reacted with antibody found in sera from all patients with tuberculosis and with antibody from over 25% of the control individuals. A 10,000-molecular-weight antigen, a 30,000- to 44,000-molecular-weight antigen, and a heterogeneous high-molecular-weight antigen were observed in the polysaccharide II fraction; these antigens reacted with serum antibody from 70% or more of the patients with tuberculosis and with antibody from 20 to 70% of the control individuals. One of the antigens, with a molecular weight ranging from 17,000 to 28,000 in the polysaccharide II fraction, reacted with antibody in 64% of the sera from patients with tuberculosis but with only 1 of 15 control normal sera. This antigen may elicit an antibody response specifically associated with tuberculosis.