Leukocyte counts and macrophage phenotypes in induced sputum and bronchoalveolar lavage fluid from normal subjects

It is unclear whether leukocytes in induced sputum (IS) and bronchoalveolar lavage (BAL) represent the same cell populations. To compare leukocyte counts and macrophage phenotypes and investigate any measurable dithiothreitol (DTT)-mediated effect on macrophage immunocytochemical staining results, IS and BAL samples from nine healthy smokers and seven nonsmokers were examined. BAL and IS samples were processed and cell viability and cell counts were assessed. The macrophages were characterized by seven monoclonal antibodies (RFD1, RFD7, CD11b, CD54, CD68, CD71 and HLA-DR) using an indirect immunoalkaline phosphatase method. Intraindividual comparison of IS and BAL showed that IS samples from smokers and nonsmokers contained a lower total cell count (p<0.01 smokers, p<0.05 nonsmokers), a lower percentage of macrophages (both p<0.05) and a higher percentage of neutrophils (both p<0.05) than BAL samples. In addition, nonsmokers sputum samples contained a lower proportion of lymphocytes (p<0.05) than BAL. The macrophage expression of RFD7 and CD71 was higher in smokers sputum samples (both p<0.05) than in BAL, while nonsmokers sputum macrophages showed a higher expression of CD54 and CD71 (both p<0.05) than BAL macrophages. DTT-incubated BAL samples showed no difference in macrophage antigen expression from BAL samples not exposed to DTT. In conclusion, the relative proportions of leukocytes and the macrophage phenotypes differed between induced sputum and bronchoalveolar lavage suggesting that the methods provide samples from different lung compartments, inhabited by cells with different phenotypes.