Relationship of immunodiagnostic assays for tuberculosis and numbers of circulating CD4+ T-cells in HIV infection.

Infection with HIV is the greatest risk factor for tuberculosis (TB) in Africa. Tuberculin skin test (TST), QuantiFERON-TB Gold In-Tube (QFT-G-IT) and T-Spot.TB assays were performed in newly diagnosed HIV-infected individuals with and without active TB and in HIV-uninfected subjects at a university outpatient clinic in Kampala, Uganda. A total of 135 individuals were enrolled: 109 with a new diagnosis of HIV-1 infection but no active TB, 19 with HIV-1 infection and active TB, and seven HIV-uninfected healthy subjects. In control subjects immune responses were positive in 57.2% by TST and in 100% by at least one interferon-gamma release assay. In HIV-1 infected patients without active TB, induration in the TST (mm) (rho = 0.41, p-value <0.0001) and concentration of interferon (IFN)-gamma in the QFT-G-IT tube with Mycobacterium tuberculosis-specific antigens (rho = 0.38; p = 0.0001) were negatively correlated to numbers of circulating CD4+ T-cells, while numbers of IFN-gamma producing cells (rho = 0.03-0.13; p-value = 0.21-0.77) and frequencies of positive test results for the T-Spot.TB test among groups of patients with different levels of immunodeficiency remained constant (p-value = 0.46). In HIV-1 infection, TST and QFT-G-IT immune responses are both strongly related to the degree of immunodeficiency, while results of the T-Spot.TB are independent of the level of CD4+ T-cell depletion.