Identification and Characterization of the ESAT-6 Homologue ofMycobacterium lepraeand T-Cell Cross-Reactivity withMycobacterium tuberculosis

Abstract

In this paper we describe identification and characterization of Mycobacterium leprae ESAT-6 (L-ESAT-6), the homologue of M. tuberculosis ESAT-6 (T-ESAT-6). T-ESAT-6 is expressed by all pathogenic strains belonging to the M. tuberculosis complex but is absent from virtually all other mycobacterial species, and it is a promising antigen for immunodiagnosis of tuberculosis (TB). Therefore, we analyzed whether L-ESAT-6 is a similarly powerful tool for the study of leprosy by examining T-cell responses against L-ESAT-6 in leprosy patients, TB patients, and exposed or nonexposed healthy controls from areas where leprosy and TB are endemic and areas where they are not endemic. L-ESAT-6 was recognized by T cells from leprosy patients, TB patients, individuals who had contact with TB patients, and healthy individuals from an area where TB and leprosy are endemic but not by T cells from individuals who were not exposed to M. tuberculosis and M. leprae. Moreover, leprosy patients who were not responsive to M. leprae failed to respond to L-ESAT-6. A very similar pattern was obtained with T-ESAT-6. These results show that L-ESAT-6 is a potent M. leprae antigen that stimulates T-celldependent gamma interferon production in a large proportion of individuals exposed to M. leprae. Moreover, our results suggest that there is significant cross-reactivity between T-ESAT-6 and L-ESAT-6, which has implications for the use of ESAT-6 as tool for diagnosis of leprosy and TB in areas where both diseases are endemic.Tuberculosis (TB) and leprosy are major public health problems in the developing world. One-third of the world's population is infected with Mycobacterium tuberculosis, and around 2 million individuals suffer from leprosy (9). Many studies have shown that early culture filtrate proteins of M. tuberculosis can be dominant target antigens for CD4 ϩ Th1 cells both in animal models of TB (1, 2, 5, 12, 13) and in humans. One of these secreted antigens, called T-ESAT-6, is a 10-kDa protein which is present in M. tuberculosis and virulent M. bovis but not in M. bovis BCG, and this protein could not be detected in M. leprae, M. avium, M. scrofulaceum, M. intracellulare, M. fortuitum, and M. xenopi (3, 11). Indeed, when the T-ESAT-6 protein was used, TB-infected cattle could be distinguished from cattle sensitized by environmental mycobacteria (15), and in humans T-ESAT-6 and T-ESAT-6-derived peptides were shown to be very efficiently and specifically recognized by individuals exposed to M. tuberculosis (4,14,16,21). The gene for ESAT-6 (Rv3875) is in a region of the M. tuberculosis genome, designated RD1, that is indeed absent from M. bovis BCG and most nontuberculous mycobacteria (NTM).The existing diagnostic skin test reagents for leprosy, lepromin and leprosin, are prepared from whole autoclaved M. leprae and from the soluble fraction of M. leprae, respectively, and contain many mycobacterial antigens shared with other species (20). A more specific skin test reagent for leprosy would be a highly desirable diagnostic tool. Becaus...

Interferon Gamma Response to Combinations 38 kDa/CFP‐10, 38 kDa/MPT‐64, ESAT‐6/MPT‐64 and ESAT‐6/CFP‐10, Each Related to a Single Recombinant Protein of Mycobacterium tuberculosis in Individuals from Tuberculosis Endemic Areas

“…TST ϩ individuals considered as having latent infection have demonstrated a higher proliferative response to ESAT-6 and its combination with CFP-10, suggesting their possibility as indicators for latent infection or as a diagnostic compound (10,16,25,31). However, in populations inhabiting tropical areas where human mycobacteriosis are endemic, new studies must be undertaken as IFN-γ production in healthy donors from this type of geographic area may merely represent a cross-reactive immune response to exposure to leprosy, environmental atypical mycobacteria or orthologs present in other bacterial species (4,14,15). More recently, ESAT-6 has been reported as a marker for infection but less effective for latent infection, while 16 kDa was suggested to be a potential marker for latently infected individuals (6).…”

MHC class II Tetramer Guided Detection of Mycobacterium tuberculosis‐specific CD4+ T Cells in Peripheral Blood from Patients with Pulmonary Tuberculosis

“…The expression of ESAT-6 is largely restricted to organisms of the TB complex (although an analogue is found in M. leprae) but not in BCG or MOTT which makes this protein attractive as both a vaccine candidate and a target for gauging bona fide MTB-specific T-cell responses [26,27]. Immune reactivity directed against ESAT-6, as defined by an ELI-SPOT, may also aid in establishing an early diagnosis of subclinical active tuberculosis in immune-suppressed patients [28].…”

Diagnostic Implications of Antigen-Induced Gamma Interferon Production by Blood Leukocytes from Mycobacterium bovis -Infected Reindeer ( Rangifer tarandus )

“…In particular, use of these antigens can enhance the specificity of IFN-␥-based tests over that achieved when standard PPDs are used as the eliciting agent. However, humans infected with Mycobacterium leprae, Mycobacterium marinum, or M. kansasii exhibit recall IFN-␥ responses to ESAT-6 and/or CFP-10, indicating that T-cell responses to these two proteins are not invariably specific for infection with M. tuberculosis complex mycobacteria (1,8,9,10). In the present study, CFP-10 and a fusion protein of ESAT-6 and CFP-10 elicited robust recall IFN-␥ responses by blood leukocytes from M. bovis-infected reindeer.…”