Antibodies against Mycobacterial Proteins as Biomarkers for HIV-Associated Smear-Negative Tuberculosis

Serology data are limited for patients with sputum smear-negative HIV-associated active tuberculosis (TB). We evaluated the serum antibody responses against the mycobacterial proteins MPT51, MS, and echA1 and the 38-kDa protein via enzyme-linked immunosorbent assay (ELISA) in South African (S.A.) HIV-positive (HIV+) smear-negative TB patients (n = 56), U. S. HIV+ controls with a positive tuberculin skin test (TST+; n = 21), and S. A. HIV-negative (HIV-) (n = 18) and HIV+ (n = 24) controls. TB patients had positive antibody reactivity against MPT51 (73%), echA1 (59%), MS (36%), and the 38-kDa protein (11%). Little reactivity against MPT51 and echA1 was observed in control groups at low risk for TB, i.e., S.A. HIV- (0% and 6%, respectively), and at moderate risk for TB development, i.e., U.S. HIV+ TST+ controls (14% and 10%, respectively). By contrast, more reactivity was detected in the S.A. HIV+ control group at higher risk for TB (25% and 45%, respectively). Our data hold promise that antibody detection against MPT51 and echA1 might have adjunctive value in the detection of HIV+ smear-negative TB and might reflect increasing Mycobacterium tuberculosis infection activity in asymptomatic HIV+ individuals.