Pulmonary alveolar proteinosis (PAP) is an idiopathic lung disease in which the alveolar spaces are filled with surfactant. Recently, it has been proposed that PAP is caused by deficiency of granulocyte-macrophage colony-stimulating factor (GM-CSF) because GM-CSF-knockout mice develop the disease. To examine this possibility, we tested the two hypotheses that lung GM-CSF levels are low and that alveolar macrophages (AM) do not respond to GM-CSF in patients with PAP. Data from 10 adult patients with PAP who underwent therapeutic whole-lung lavage were compared with those of 10 healthy volunteers who underwent bronchoalveolar lavage (BAL) by fiberoptic bronchoscopy. Bronchoalveolar lavage fluid (BALF) and plasma were collected and analyzed for total protein and levels of GM-CSF, interleukin-3, and tumor necrosis factor (TNF)-alpha. Isolated AM were cultured with or without lipopolysaccharide (LPS) or GM-CSF, and production of GM-CSF and TNF-alpha was measured after 24 h. GM-CSF in BALF and plasma was higher in PAP than in control subjects (p </= 0.05), and was detectable under both reducing and nonreducing conditions as a 28-kD protein in BALF from the PAP patients. GM-CSF release by unstimulated AM from PAP patients was higher than in cells from control subjects, but the responses to LPS were similar. Mean TNF-alpha release by AM in response to GM-CSF was higher in control subjects than in PAP patients due to a low response in three patients. In conclusion, unbound immunoreactive GM-CSF is detectable in BALF and plasma of PAP patients. Most PAP patients also had intact AM responses to GM-CSF, although some may have had defects in GM-CSF receptor or signal-transduction mechanisms. Although these data exclude lack of GM-CSF production as a common etiology of human PAP, defects in GM-CSF function in PAP are under investigation.