Background: Tuberculosis (TB) causes about 3 million of death per year. It is very important to elucidate the precise mechanism of defense against Mycobacterium tuberculosis. The role of gamma-delta (/9) T lymphocytes in adaptative immunity in tuberculosis remains uncertain. We addressed the distribution of these T subsets at diagnosis of tuberculosis patients and suggest they must be involved in the pathogenesis of the disease. Methods: The frequency of /9 T lymphocytes was evaluated in both pleural effusion and peripheral blood of 33 patients with pleural tuberculosis before treatment. Frozen PBMCs were surface stained for CD3, V91, and V92. Analyze of memory and naive subsets were performed by expression of CD11a and CD27 on /9 T cell. Also, the percentage of IFN-/- producing V91 and V92 cells after IPP stimulation was evaluated. Latently infected contacts and healthy subjects were used as controls. Results: The latent infection group presented the highest proportion of V91 T cells (12.9%, p < 0.05) compared to healthy control (4.29%, p < 0.05) and tuberculosis patients (6.2%, p < 0.05). It was observed higher percentage of memory cells in latent infection than the other groups (p < 0.05). Pleural effusion was characterized by higher frequency of memory phenotype cells than blood (p = 0.0342). These subsets produced more IFNg (7.05% in memory versus 3.62% in naíve cells, p < 0.05) confirming that they are memory cells. We found that in tuberculosis the frequency of V91T cells are higher when compared with V92 (5.07% versus 1.1%, p < 0.05). These numbers reflected an inverted V91:Vd2 ratio associated with tuberculosis. The latent infection group presented higher frequency of V92 T cells than healthy control (2.76% versus 1.29%, p = 0.03), and than TB (p < 0.001). Conclusion: Marked accumulation of V91 and V92 in pleural effusion is seen in active tuberculosis, and /9 T lymphocytes are expanded in pleural effusion, and this site is mainly composed by memory subsets. Our date further indicate that /9 T cells participate in the immune response against Mycobacterium tuberculosis.
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