Patients infected with tuberculosis, HIV, or both have low levels of circulating (gamma)(delta) T cells, researchers report in the April issue of Thorax (2002;57;4:357-360).

"Several recent studies suggest that (gamma)(delta) T lymphocytes play an important role in immunity against Mycobacterium tuberculosis," explained Dr. A.C.C. Carvalho and colleagues at the Federal University of Clementino Fraga Filho University Hospital in Rio de Janeiro, Brazil, and the University of Brescia and Spedali Civili Hospital in Brescia, Italy. "However, the dynamics of these cells in the peripheral blood of patients with tuberculosis with and without HIV infection is not fully understood." Both HIV infection and tuberculosis were associated with reduced levels of (gamma)(delta) T cells in peripheral blood, Carvalho and coauthors found.

The researchers evaluated T cell populations in 74 TB patients, 20 of whom were coinfected with HIV. T cell counts in these patients were compared with those seen in healthy blood donors and asymptomatic HIV patients, they said. Although (gamma)(delta) 1 T lymphocytes were present at similar levels in all groups, TB patients had significantly lower levels of the (gamma)(delta) 2 subset compared with controls. Reduced (gamma)(delta) 2 cell counts were also seen in HIV patients with or without TB coinfection, study data showed.

"HIV seronegative TB patients and HIV infected individuals (with or without active TB) have a reduced number of circulating V (delta)(gamma) 2 T cells compared with healthy individuals," Carvalho and colleagues concluded. "Whether TB and HIV infection share a common mechanism causing V (delta)(gamma) 2 T cell depletion still needs to be established."

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