Mycobacterium tuberculosis epitope-specific interferon-g production in healthy Brazilians reactive and non-reactive to tuberculin skin test

The interferon (IFN)-γ response to peptides can be a useful diagnostic marker ofMycobacterium tuberculosis (MTB) latent infection. We identified promiscuous andpotentially protective CD4⁺ T-cell epitopes from the most conservedregions of MTB antigenic proteins by scanning the MTB antigenic proteins GroEL2,phosphate-binding protein 1 precursor and 19 kDa antigen with the TEPITOPE algorithm.Seven peptide sequences predicted to bind to multiple human leukocyte antigen(HLA)-DR molecules were synthesised and tested with IFN-γ enzyme-linked immunospot(ELISPOT) assays using peripheral blood mononuclear cells (PBMCs) from 16 Mantouxtuberculin skin test (TST)-positive and 16 TST-negative healthy donors. Eighty-eightpercent of TST-positive donors responded to at least one of the peptides, compared to25% of TST-negative donors. Each individual peptide induced IFN-γ production by PBMCsfrom at least 31% of the TST-positive donors. The magnitude of the response againstall peptides was 182 ± 230 x 10⁶ IFN-γ spot forming cells (SFC) amongTST-positive donors and 36 ± 62 x 10⁶ SFC among TST-negative donors (p =0.007). The response to GroEL2 (463-477) was only observed in the TST-positive group.This combination of novel MTB CD4 T-cell epitopes should be tested in a larger cohortof individuals with latent tuberculosis (TB) to evaluate its potential to diagnoselatent TB and it may be included in ELISPOT-based IFN-γ assays to identifyindividuals with this condition.