Long-lived immune response to early secretory antigenic target 6 in individuals who had recovered from tuberculosis

We sought to understand the persistence and relevance of the long-lived imm une response to early secretory antigenic target (ESAT-6) of Mycobacterium tuberculosis in humans. ESAT-6 is recognized by memory cells involved in pr otection of animals against tuberculosis (TB). Recent reports also showed t hat ESAT-6 response can be recovered in patients with TB and in those soon after anti-TB therapy. We chose 18 individuals who had recovered from pulmo nary TB (some in remission for >5 years), and 14 bacille Calmette-Guerin-va ccinated healthy individuals for this study. The results showed that periph eral blood mononuclear cells of 10 (55.6%) of 18 patients with TB remission responded to ESAT-6 with stimulation indices >3.0, whereas none of the hea lthy controls responded. Functional analysis showed that 13 (72.2%) of 18 p atients with TB remission produced significant amounts of IFN-gamma in resp onse to ESAT-6, whereas only 1 (7.1%) of the 14 healthy control subjects di d so. It appears that responses to ESAT-6 can persist in individuals who ha d recovered from pulmonary TB.