A simple sensitive and specific point-of-care test that can diagnose TB in both HIV- and HIV+ subjects is urgently needed for combating the raging TB epidemic. A subfamily of genes, called PE-PGRS genes is present in M. tuberculosis (complex), but there are no PE-PGRS genes in several other common mycobacterial pathogens including M. avium (which afflicts 5-7% of the HIV+ subjects) and M. leprae. This makes the PE-PGRS proteins attractive targets for inclusion into diagnostic tests for TB. Our preliminary studies demonstrate that immunodominant epitopes that are shared by several PE-PGRS proteins (promiscuous epitopes) are highly immunogenic in TB patients. Based on these results we propose to identify the PE-PGRS genes that are highly expressed in the lungs of tuberculous rabbits infected with aerosols of clinical isolates of M. tuberculosis, and map their immunodominant promiscuous epitopes recognized specifically by antibodies from HIV-TB+ and HIV+TB+ patients. These epitopes can be the basis of a simple peptide-based diagnostic test for TB. Specifically, we propose to: a) Identify the subset of PE-PGRS genes that is highly expressed by M. tuberculosis during growth and replication in lungs, and characterize the proteins (Aim #1);b) Dissect the PEPGRS proteins selected in Aim # 1 to delineate the immunodominant epitopes that are recognized by serum antibodies from HIV-TB+ and HIV+TB+ patients but not by PPD-, PPD+ and/or BCG vaccinated healthy subjects or HIV+TB- controls (Aim #2) and c) Evaluate the reactivity of epitopes identified in Aim #2 with sera from individual patients at different stages of TB to identify the optimal set of peptides and evaluate the optimal peptide-subset for reactivity with sera from patients from different geographical settings (Aim # 3).
The work proposed could lead to development of a cheap, reliable and rapid diagnostic test for TB. No reliable rapid tests for TB exist so far and this would be a major advancement in the field.
