The results suggest that frequent recognition of the M. tuberculosisESAT-6 antigen by T cells from patients with tuberculosis is due to the presence of multiple epitopes scattered throughout the ESAT-6 sequence.
However, to obtain specificity, it is necessary to include quantitative IFN-gamma 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.
Some of these antigens have shown promise as new candidate vaccines (hsp60, Ag85 and ESAT-6, etc.) and specific diagnostic reagents (ESAT-6 and CFP10, etc.) for TB.
Response of IFN-gamma and IgG to ESAT-6 and 38 kDa recombinant proteins and their peptides from Mycobacterium tuberculosis in tuberculosis patients and asymptomatic household contacts may indicate possible early-stage infection in the latter.
Antibodies to the 38-kDa antigen, alanine dehydrogenase, and Rv2626c were associated with active TB, while antibodies to the 16-kDa antigen, ferredoxin A, and ESAT-6 were associated with inactive TB.
The T cell response to early secreted antigenic target, 6 kDa (ESAT-6), was attenuated in patients with tuberculosis (odds ratio [OR], 0.41 [95% confidence interval {CI}, 0.19-0.89]; P = .024) and household contacts (OR, 0.56 [95% CI, 0.38-0.83]; P = .004) infected with M. africanum, compared with the response in those infected with M. tuberculosis.
We then compared cytokine expression to their recognition of ESAT-6 (which is largely restricted to members of the tuberculosis complex and which serves as a reliable marker of infection) or to Ag85A (an antigen that is conserved among the mycobacteria and serves as a nonspecific control).
The ESAT-6 PCR detected all of the M. tuberculosis strains correctly (100% sensitivity), but none of the nontuberculous Mycobacterium spp. gave positive results (100% specific).
In contrast, responses to latency antigens were observed in individuals with suspected exposure to TB (as indicated by positive gamma interferon responses to TB-specific antigens ESAT-6 and CFP-10) and in mice vaccinated with plasmid DNA encoding selected latency antigens.
Adoptive transfer of activated ESAT-6-specific Th1 cells into naive recipients before aerosol M. tuberculosis infection dramatically enhances resistance, resulting in 100-fold fewer bacteria in infected lungs.
Recognition of the Rv0222 was compared with the 38 kDa protein and a fusion protein of the RD1 proteins ESAT-6 and CFP10 in a serum panel from pulmonary tuberculosis (TB) patients from Uganda.
The ess locus is a cluster of eight genes (esxAB, essABC, esaABC) of which esxA and esxB display homology to secreted ESAT-6 proteins of Mycobacterium tuberculosis.
Combination of Ppe57 or NrdF1 with early secreted antigen target 6 (ESAT-6) or 10-kDa culture filtrate protein (CFP-10) in the IFN-gamma releasing ESLIPOT assay could increase the sensitivities in detecting active TB, for ESAT-6 from 82.1% to 85.7% or 92.9% (P=0.5 or 0.03, respectively) and for CFP-10 from 67.9% to 78.6% or 83.9%, respectively (both P<0.05).
Taken together, ESAT-6/CFP-10 cytokine tests together with detecting IgG antibodies specific to ESAT-6 and CFP-10 may be the useful TB disease biomarkers in monitoring treatment success.
In conclusion, the ESAT-6 test may be the most appropriate for diagnosis of childhood TB, both LTBI and TB disease, when associated with epidemiological and clinical data, especially in endemic areas such as Brazil.
In particular, stimulation with Ag85B240-259, strong specific Th1 type cellular immunity was elicited by vaccination C57BL/6 mice with hly deficient strain delivering Mycobacterium tuberculosis fusion antigen Ag85B-ESAT-6 via intravenous inoculation.