γδ T lymphocytes in the peripheral blood of patients with tuberculosis with and without HIV co-infection

Background: Several recent studies suggest that gamma(delta) T lymphocytes play an important role in immunity against Mycobacterium tuberculosis. However, the dynamics of these cells in the peripheral blood of patients with tuberculosis (TB) with and without HIV infection is not fully understood. A study was undertaken to evaluate the profile of the gamma(delta) T cell population in patients at the time the diagnosis of TB was established. Methods: A cross sectional study was performed in consecutive TB patients from the Department of Infectious Diseases, Spedali Civili, Brescia. CD4+, CD8+ and Vdelta1 and Vdelta2 T cell counts were analysed. Lymphocyte surface membrane expression was evaluated with the FITC-TCRgamma6, -Vdelta1, Vdelta2 and PE-Vdelta1 monoclonal antibodies. Blood donors and HIV seropositive asymptomatic individuals acted as controls. Results: Seventy four TB patients were evaluated 20 of whom (27%) were co-infected with HIV. HIV seronegative TB patients (n=54) had total gamma(delta) T cells and Vdelta1 subsets comparable to those in blood donors (n=39). However, the percentage with the Vdelta2 subset was significantly lower in patients with TB than in controls (median 1.5 v 2.1; p=0.05). Responsiveness to PPD was not associated with predominance of a specific gamma(delta) T cell subset. HIV seropositive individuals had a decreased percentage of circulating Vdelta2 cells at a level similar to that in HIV seronegative TB patients, regardless of the presence of active TB. Conclusions: HIV seronegative TB patients and HIV infected individuals with or without active TB have a reduced number of circulating Vdelta2 T cells compared with healthy individuals. Whether TB and HIV infection share a common mechanism causing Vdelta2 T cell depletion still needs to be established.