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.