title: Characterization of a cross-reactive, immunodominant and HLA-promiscuous epitope of Mycobacterium tuberculosis-specific major antigenic protein PPE68.
abstract: PPE68 (Rv3873), a major antignic protein encoded by Mycobacteriun tuberculosis-specific genomic region of difference (RD)1, is a strong stimulator of peripheral blood mononuclear cells (PBMCs) obtained from tuberculosis patients and Mycobacterium bovis bacillus Calmette Guerin (BCG)-vaccianted healthy subjects in T helper (Th)1 cell assays, i.e. antigen-induced proliferation and interferon-gamma (IFN-γ) secretion. To confirm the antigen-specific recognition of PPE68 by T cells in IFN-γ assays, antigen-induced human T-cell lines were established from PBMCs of M. Bovis BCG-vaccinated and HLA-heterogeneous healthy subjects and tested with peptide pools of RD1 proteins. The results showed that PPE68 was recognized by antigen-specific T-cell lines from HLA-heteregeneous subjects. To further identify the immunodominant and HLA-promiscuous Th1-1 cell epitopes present in PPE68, 24 synthetic peptides covering the sequence of PPE68 were indivdually analyzed for HLA-DR binding prediction analysis and tested with PBMCs from M. bovis BCG-vaccinated and HLA-heterogeuous healthy subjects in IFN-γ assays. The results identified the peptide P9, i.e. aa 121-VLTATNFFGINTIPIALTEMDYFIR-145, as an immunodominant and HLA-DR promiscuous peptide of PPE68. Furthermore, by using deletion peptides, the immunodominant and HLA-DR promiscuous core sequence was mapped to aa 127-FFGINTIPIA-136. Interestingly, the core sequence is present in several PPE proteins of M. tuberculosis, and conserved in all sequenced strains/species of M. tuberculosis and M. tuberculosis complex, and several other pathogenic mycobacterial species, including M. leprae and M. avium-intracellulalae complex. These results suggest that the peptide aa 121-145 may be exploited as a peptide-based vaccine candidate against tuberculosis and other mycobacterial diseases.
authors.affiliation: Department of Microbiology, Faculty of Medicine, Kuwait University, Safat, Kuwait.
authors.forename: Abu S
authors.initials: AS
authors.lastname: Mustafa
mesh_terms: D000595:Amino Acid Sequence; D000942:Antigens, Bacterial / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D001500:BCG Vaccine / Q000008:administration & dosage; D001426:Bacterial Proteins / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D001665:Binding Sites; D017124:Conserved Sequence; D003429:Cross Reactions; D018984:Epitopes, T-Lymphocyte / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D006684:HLA-DR Antigens / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D007371:Interferon-gamma / Q000096:biosynthesis; D008969:Molecular Sequence Data; D015269:Mycobacterium avium Complex / Q000235:genetics / Q000276:immunology; D009166:Mycobacterium leprae / Q000235:genetics / Q000276:immunology; D009169:Mycobacterium tuberculosis / Q000235:genetics / Q000276:immunology*; D010449:Peptide Mapping; D061251:Primary Cell Culture; D016415:Sequence Alignment; D018417:Th1 Cells / Q000737:chemistry / Q000276:immunology; D014397:Tuberculosis, Pulmonary / Q000276:immunology / Q000382:microbiology / Q000517:prevention & control*; D014611:Vaccination
chemical_list: D000942:Antigens, Bacterial; D001500:BCG Vaccine; D001426:Bacterial Proteins; D018984:Epitopes, T-Lymphocyte; D006684:HLA-DR Antigens; C528814:PPE68 protein, Mycobacterium tuberculosis; D007371:Interferon-gamma