Immune response to Mycobacterium tuberculosis specific antigen ESAT-6 among south Indians.

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-gamma) 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 (76pg/ml), Esp6 (64pg/ml), induced IFN-gamma production in HHC; PTB gave low IFN-gamma responses for the peptides. TR responded to the peptides Esp1 (141pg/ml), Esp8 (102pg/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 DRB104 and HLA DRB110 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.