Cellular immune responses to ESAT-6 discriminate between patients with pulmonary disease due to Mycobacterium avium complex and those with pulmonary disease due to Mycobacterium tuberculosis

ESAT-6 (for 6-kDa early secreted antigenic target) is a secreted antigen fo und almost exclusively in organisms of the Mycobacterium tuberculosis compl ex. We compared in vitro gamma interferon (IFN-gamma) responses by peripher al blood mononuclear cells to this antigen in patients with pulmonary disea se due to either Mycobacterium avium complex (MAC) or Mycobacterium tubercu losis with those in healthy, skin test-negative, control subjects. Signific ant IFN-gamma responses to ESAT-6 were detected in 16 (59%) of 27 M, tuberc ulosis pulmonary disease patients, 0 (0%) of 8 MAC disease patients, and 0 (0%) of 8 controls. Significant IFN-gamma responses to M, tuberculosis puri fied protein derivative were detected in 23 (85%) of 27 M, tuberculosis dis ease patients, 2 (25%) of 8 MAC disease patients, and 5 (63%) of 8 healthy controls. M, avium sensitin was recognized in 24 (89%) of 27 M, tuberculosi s disease patients, 4 (50%) of 8 MAC disease patients, and 1 (13%) of 8 con trols. IFN-gamma responses to ESAT-6 are specific for disease due to M, tub erculosis and are not observed in patients with MAC disease or in healthy c ontrols.