Immunological Diagnosis of Tuberculosis Based on Recombinant Antigens ESAT-6 and CFP-10 in Children from an Endemic Area in Northeast Brazil

The TB-specific CD4(+) T cell immune repertoire in both cynomolgus and rhesus macaques largely overlap with humans

Non-human primate (NHP) models of tuberculosis (TB) immunity and pathogenesis, especially rhesus and cynomolgus macaques, are particularly attractive because of the high similarity of the human and macaque immune systems. However, little is known about the MHC class II epitopes recognized in macaques, thus hindering the establishment of immune correlates of immunopathology and protective vaccination. We characterized immune responses in rhesus macaques vaccinated against and/or infected with Mycobacterium tuberculosis (Mtb), to a panel of antigens currently in human vaccine trials. We defined 54 new immunodominant CD4(+) T cell epitopes, and noted that antigens immunodominant in humans are also immunodominant in rhesus macaques, including Rv3875 (ESAT-6) and Rv3874 (CFP10). Pedigree and inferred restriction analysis demonstrated that this phenomenon was not due to common ancestry or inbreeding, but rather presentation by common alleles, as well as, promiscuous binding. Experiments using a second cohort of rhesus macaques demonstrated that a pool of epitopes defined in the previous experiments can be used to detect T cell responses in over 75% of individual monkeys. Additionally, 100% of cynomolgus macaques, irrespective of their latent or active TB status, responded to rhesus and human defined epitope pools. Thus, these findings reveal an unexpected general repertoire overlap between MHC class II epitopes recognized in both species of macaques and in humans, showing that epitope pools defined in humans can also be used to characterize macaque responses, despite differences in species and antigen exposure. The results have general implications for the evaluation of new vaccines and diagnostics in NHPs, and immediate applicability in the setting of macaque models of TB.

Mycobacterium tuberculosis Sonicate-Induced IFNγ, CXCL10 and IL10 can Differentiate Severity in Tuberculosis

Improved tools are required to study immunopathogenesis of tuberculosis (TB). Mycobacterium tuberculosis antigen-stimulated T cell-based assays can detect TB but are less effective when responses are compromised such as in severe disease. We investigated immune responses to M. tuberculosis whole sonicate (MTBs), recombinant antigens ESAT6 and CFP10 in whole blood cells of healthy endemic controls (EC, n = 42) and patients with pulmonary (PTB, n = 36) or extrapulmonary (ETB, n = 41) disease. Biomarkers of T cell activation (IFNγ) or modulation (IL10) and chemokines, CXCL9, CXCL10 and CCL2, secretion were measured. MTBs, ESAT6 and CFP10 all induced IFNγ responses in TB. ESAT6-induced IFNγ was elevated in TB as compared with EC. MTBs stimulated the highest IFNγ levels but did not differentiate between TB and EC. However, MTBs-induced CXCL10 (P = 0.004) was reduced, while IL10 (P < 0.001) was raised in TB as compared with EC. Between sites, MTBs-induced CCL2 (P = 0.001) and IL10 secretion was higher in PTB than ETB (P < 0.001). In comparison of disease severity, MTBs-induced IFNγ (P = 0.014) and CXCL10 (P = 0.022) levels were raised in moderate as compared with far advanced PTB. In ETB, MTBs-induced IL10 levels were greater in less-severe (L-ETB) than in severe disseminated (D-ETB) cases, P = 0.035. Within the L-ETB group, MTBs-induced IFNγ was greater in patients with tuberculous lymphadenitis than those with pleural TB (P = 0.002). As immune responses to MTBs were differentially activated in TB of different sites and severity, we propose the utility of MTBs-induced IFNγ, CXCL10 and IL10 as biomarkers in TB.

Expression and Purification of Recombinant Mycobacterium Tuberculosis (TB) Antigens, ESAT-6, CFP-10 and ESAT- 6/CFP-10 and Their Diagnosis Potential for Detection of TB Patients

BACKGROUND

One of the most widely used methods to detect tuberculosis (TB) infection is the tuberculin skin test (TST). The completion of Mycobacterium tuberculosis (M. tuberculosis) genome sequence has led to identification of several antigens that can be utilized for accurate diagnosis and control of TB. The aim of this study was to purify the recombinant M. tuberculosis antigens for the evaluation of their potential in TB diagnosis.

METHODS

The recombinant secretory antigens, ESAT-6, CFP-10 and ESAT-6/CFP-10 were produced by PCR and cloning methods. To investigate antigen specific responses of these recombinant antigens in detection of TB, ex vivo enzyme linked immunospot (ELISPOT) test in 30 clinically diagnosed TB patients was evaluated.

RESULTS

The selected M. tuberculosis antigens were cloned, expressed and purified in Escherichia coli (BL21). ELISPOT assay for detection of TB showed the sensitivity of 93, 90 and 100% for recombinant ESAT-6, CFP-10 and ESAT-6/CFP-10 proteins respectively, which is significantly higher than conventional TST.

CONCLUSION

The recombinant antigens of ESAT-6, CFP-10 and ESAT-6/CFP-10 can be used as an accurate means of detecting TB in Iran.