Alveolar macrophage subpopulations in patients with active pulmonary tuberculosis

Alveolar macrophages are a heterogeneous cell population. The heterogeneity of alveolar macrophages recovered by bronchoalveolar lavage (BAL) from 12 patients with active pulmonary tuberculosis (TB) and 10 normal subjects was studied using Percoll density fractionation. The numbers and subsets (on the basis of CD3, CD4, and CD8 monoclonal antibodies) of lymphocytes in BAL were measured by flow cytometry. Alveolar macrophages recovered from patients with TB were mainly in the lower-density fractions (<1.030 and 1.030 to 1.040 g/ml), whereas alveolar macrophages from normal subjects were in the higher-density fractions (1.050 to 1.070 and >1.070 g/ml). There were no significant differences in alveolar macrophages' repartition between smokers and nonsmokers in either patients with TB or normal subjects. The significant changes in the proportions of the lowest fraction and the higher fractions of alveolar macrophages in patients with TB were not altered after division of our patients into smoker and nonsmoker subgroups when compared with corresponding subgroups in normal subjects. The proportion of the alveolar macrophages in the lowest fraction was inversely related to the bacterial load of sputum and the disease extent on chest radiography in TB patients. The CD4/CD8 ratio was significantly higher in patients with TB. This study shows that alveolar macrophages from TB patients are heterogeneous with hypodense cells predominant probably by interaction with T lymphocytes. Changes in the proportions of alveolar macrophages within subpopulations may be of critical importance in determining the overall response of the lung to TB infection.