Characterization of colony stimulating factor activity in the human respiratory tract. Comparison of healthy smokers and nonsmokers.

The number and function of pulmonary macrophages are critical to lung homeostasis. To characterize factors normally present in the human respiratory tract that can influence these parameters, bronchoalveolar lavage (BAL) fluid obtained from healthy smokers and nonsmokers was assayed for the presence of colony-stimulating factor (CSF) activity. Concentrated BAL fluid from both populations was capable of inducing incorporation of [3H]thymidine by murine macrophages. The mean increase (+/- SEM) in incorporation over control cultures not exposed to BAL fluid was 0.98 +/- 0.22 for nonsmokers and 2.25 +/- 1.19 for smokers (p less than 0.001). This CSF bioactivity was characterized as macrophage-CSF (M-CSF) by virtue of its action on murine macrophages, the detection of M-CSF protein by a specific ELISA assay, and the inability to detect other macrophage-active CSFs, granulocyte macrophage-CSF (GM-CSF) and interleukin-3 (IL-3), in a proliferation assay employing the MO7E cell line. There was a significant correlation between macrophage number in BAL samples and measureable bioactivity among both smokers and nonsmokers (r = 0.763; p less than 0.001). This suggested that macrophages themselves are a source of the M-CSF detected in BAL fluid. To examine this possibility, slot-blot analysis of macrophage RNA was performed. Constitutive expression of comparable amounts of M-CSF mRNA and protein was found in cells from both smokers and nonsmokers. However, macrophages obtained from a randomly selected subset of four smokers but none of five nonsmokers exhibited increased production of M-CSF in response to an inflammatory stimulus, lipopolysaccharide (LPS; 5 ng/ml). M-CSF added to macrophage cultures was degraded by nonsmokers' cells as expected over 24 h.(ABSTRACT TRUNCATED AT 250 WORDS)