The Mycobacterium tuberculosis-specific ESAT-6 antigen induces highly potent T-cell responses and production of gamma interferon (IFN-␥), which play a critical role in protective cell-mediated immunity against tuberculosis (TB). In the present study, IFN-␥ secretion by peripheral blood mononuclear cells (PBMCs) in response to M. tuberculosis ESAT-6 in Brazilian TB patients was investigated in relation to clinical disease types, such as pleurisy and cavitary pulmonary TB. Leprosy patients, patients with pulmonary diseases other than TB, and healthy donors were assayed as control groups. Sixty percent of the TB patients indeed recognized M. tuberculosis ESAT-6, as did 50% of the leprosy patients and 60% of the non-TB controls. Nevertheless, the levels of IFN-␥ in response to the antigen ESAT, but not to antigen 85B (Ag85B) and purified protein derivative (PPD), were significantly lower in controls than in patients with treated TB or pleural or cavitary TB. Moreover, according to Mycobacterium bovis BCG vaccination status, only 59% of the vaccinated TB patients responded to ESAT in vitro, whereas 100% of them responded to PPD. Both CD4 and CD8 T cells were able to release IFN-␥ in response to ESAT. The present data demonstrate the specificity of ESAT-6 of M. tuberculosis and its ability to discriminate TB patients from controls, including leprosy patients. However, to obtain specificity, it is necessary to include quantitative IFN-␥ production in response to the antigen as well, and this might limit the use of ESAT-6-based immunodiagnosis of M. tuberculosis infection in an area of TB endemicity.Tuberculosis (TB) remains a major public health problem in the 21st century. A third of the world's population is infected with Mycobacterium tuberculosis, and 5 to 10% of the infected population will develop the disease during their lifetime. TB is responsible for more than 2 million deaths per year worldwide (9). The situation is exacerbated by coinfections with human immunodeficiency virus (HIV) and the emergence of multidrug-resistant strains of M. tuberculosis. The Mycobacterium bovis Bacillus Calmette-Guérin (BCG) vaccine is the only vaccine available against TB, and yet its efficacy is controversial. BCG has shown extremely variable levels of protection in different populations (12), ranging from 0% (38) in the study of Chingleput, South India, to 80% in The British MRC BCG Trial, Great Britain (37). A cell-mediated immune (CMI) response of the Th1 type, characterized by elevated production of gamma interferon (IFN-␥) and interleukin-12 (IL-12), is essential to mount a protective immunity against M. tuberculosis (8,13,26). Besides, a basic principle for selecting novel antigen candidates for subunit vaccine design is their capacity to induce a protective Th1 response. The definition of new antigens to be applied in an immune-based diagnostic assay for early detection of TB also has a high priority. Purified protein derivative (PPD) from M. tuberculosis is a mixture of complex antigens that has been long used as a skin...

Production of IFN-gamma guarantees helpful T cell-mediated immunity against Mycobacterium tuberculosis infection. We have evaluated the in vitro immune responses to M. tuberculosis antigens using IFN-gamma production among 43 Brazilian tuberculosis (TB) patients prior to and after specific treatment, and 18 community controls. Peripheral blood mononuclear cells (PBMC) were cultivated in the presence either of purified protein derivative, ferritin, 10 kDa, 38 kDa, MPT59, Ag85A or Ag85B. Also, the two M. tuberculosis and M. bovis heat-shock proteins (hsp) 65 and 70 kDa were compared, and 5 day supernatants were harvested for cytokine detection by ELISA. The results showed that the overall profile of primary PBMC in response to most M. tuberculosis antigens was well correlated, since high IFN-gamma levels were induced by Ag85A, Ag85B, 38 kDa, ferritin and 10 kDa, as well as M. tuberculosis hsp65 in TB patients. In addition, analysis was carried out of the in vitro expression of activation molecules on lymphocytes, as CD25 and CD69 expression assessed in 17 TB patients showed induction on CD4+ T cells by Ag85B. Overall, significantly low responses were found in untreated, in comparison with the treated TB patients. Furthermore, internal community but not healthy control individuals have higher immune responses than do TB patients.

The production of interferon γ (IFNγ) guarantees effective T cell-mediated immunity against