Increased absolute number but not proportion of γ/δ T-lymphocytes in the bronchoalveolar lavage fluid of patients with active pulmonary tuberculosis

Setting: The proportions and absolute cell count of γ/δ T-lymphocytes in the peripheral blood of patients with pulmonary tuberculosis (PTB) remains controversial. Since PTB is an infectious airway disease, bronchoalveolar T-lymphocytes should be a better indicator of local immune T-cell reaction after TB infection than peripheral blood T-lymphocytes. Objective: To quantitate the absolute cell count and proportions of γ/δ T-lymphocytes in the bronchoalveolar lavage fluid (BALF) of patients with active PTB. Design: Bronchoalveolar lavage (BAL) and analysis of lymphocytes in the BALF was performed in 25 patients with active PTB and 16 normal controls. All of the patients were negative for HIV infection and none was immunocompromized. BALF and blood were prepared for cell differential count and flow cytometry analysis using monoclonal antibodies CD3, CD4, CD8, CD25, HLA-DR and γ/δ as well as α/β T-lymphocyte receptors. Results: The number of cells per volume of recovered BALF was significantly higher in the patients with active PTB than in normal controls. BALF from active PTB patients also showed increased percentage of lymphocytes and neutrophils. The absolute number of total lymphocytes, CD3⁺ lymphocytes and CD3⁺ γ/δ T-lymphocytes were significantly higher in the BALF, but not in the blood, of patients with TB, however, the proportions of CD3⁺ γ/δ T-lymphocytes in BALF of patients with TB was comparable to that of normal controls. γ/δ T-lymphocytes in the BALF rarely expressed CD4, CD25, and HLA-DR in both groups. Conclusion: These results suggest that γ/δ T-lymphocytes are not the major subpopulation of CD3⁺ lymphocytes in the BALF that react to mycobacterial infection in the patients with clinically established active TB.