MOLECULAR AND IMMUNOLOGICAL CHARACTERIZATION OF THE HIGHLY CONSERVED ANTIGEN-84 FROM MYCOBACTERIUM-TUBERCULOSIS AND MYCOBACTERIUM-LEPRAE

Crossed immunoelectrophoresis (CIE) has been used to develop a referen ce system for classifying mycobacterial antigens. The subsequent use o f specific antibodies allowed further determination of antigens by mol ecular weight. The monoclonal antibody F126-2, originally raised again st a 34-kDa antigen of Mycobacterium kansasii, reacted with antigen 84 (Ag84) in the CIE reference system for Mycobacterium bovis BCG and il Mycobacterium tuberculosis. To characterize Ag84, we screened a lambd a gt11 gene library from M. tuberculosis with antibody F126-2 and iden tified the encoding gene. The corresponding Mycobacterium leprae Ag84 gene was subsequently selected from a cosmid library, using the M. tub erculosis gene as a probe. Both genes were expressed as 34-kDa protein s in Escherichia coli, and the recombinant proteins indeed corresponde d to Ag84 in the CIE reference system. The derived amino acid sequence s of the M. tuberculosis and M. leprae proteins showed 85% identity, w hich indicates that Ag84 constitutes a group of highly conserved mycob acterial antigens. Antibodies of almost 60% of lepromatous leprosy pat ients responded to Ag84, indicating that the protein is highly immunog enic following infection in multibacillary leprosy.