SEROLOGICAL ANALYSIS OF C-TERMINAL REGION OF ALPHA-ANTIGEN FROM MYCOBACTERIUM-AVIUM-INTRACELLULARE COMPLEX AND MYCOBACTERIUM-TUBERCULOSIS

The alpha antigen, which is a 30 kDa protein secreted by mycobacterial species, is an immunodominant antigen. The C-terminal regions of alph a antigens are highly divergent, though there are regions where the am ino acid sequence of a antigen is conserved. We investigated whether t he C-terminal regions of the Mycobacterium avium alpha antigen, M. int racellular alpha antigen and M. tuberculosis alpha antigen contain seq uence-specific B-cell epitopes. The C-terminal regions of M. avium alp ha antigen and M. intracellulare alpha antigen reacted to anti-M. aviu m alpha antigen but not to anti-M. tuberculosis alpha antigen derived from rabbits. Thus, M. avium and M. intracellulare have an antigenic d eterminant in common with rabbit. The C-terminal region of M. tubercul osis alpha antigen did not react to anti-M. avium alpha antigen or ant i-M. tuberculosis alpha antigen. An enzyme-linked immunosorbent assay revealed that only the C-terminal region of M. avium alpha antigen rea cted to the sera of two of six patients with M. avium-intracellulare ( MAC) but not to the sera of patients with M. tuberculosis. In contrast , the C-terminal regions of M. intracellulare alpha antigen and M. tub erculosis a antigen were not recognized by the sera from patients with MAC or M. tuberculosis. This region of M. avium alpha antigen can pro duce a sequence-specific B-cell epitope in humans.