The 6-kDa early secreted antigenic target (ESAT-6) is a T-cell antigen recognized by individuals infected
with Mycobacterium tuberculosis. The aim of the study was to identify ‘‘protective epitopes’’ of ESAT-6
protein in the south Indian population. Proliferative and Interferon gamma (IFN-g) responses to ESAT-6
peptides were studied by flow cytometry and Enzyme linked immunosorbent assay (ELISA). Healthy
household contacts (HHC) recognized Esp1 (10/17) and Esp6 (9/17) peptides. Among pulmonary tuberculosis
patients (PTB), Esp1 (3/11) and Esp6 (5/11) were recognized. Maximal response (7/10) was found
for Esp1 and Esp8 in treated patients (TR). Median values for the responding subjects gave the following
results: Esp1 (76 pg/ml), Esp6 (64 pg/ml), induced IFN-g production in HHC; PTB gave low IFN-g
responses for the peptides. TR responded to the peptides Esp1 (141 pg/ml), Esp8 (102 pg/ml). The
proliferation of CD4 cells was similar in both PTB and TR for all peptides; but HHC showed an increase for
Esp1 (p < 0.05) and Esp6 (p < 0.01). Esp1 (amino acids aa 1–20) and Esp6 (aa 51–70) were the immunogenic
peptides recognized by the alleles HLA DRB1*04 and HLA DRB1*10 among HHC. But the
association of the alleles with ESAT-6 peptide presentation needs to be confirmed in a large cohort of
subjects. We speculate that ESAT-6 can be used along with other immune-eliciting proteins for vaccine
design strategies in south Indian population