Pulmonary Alveolar Proteinosis Is a Disease of Decreased Availability of GM-CSF Rather than an Intrinsic Cellular Defect

Abstract

Granulocyte–macrophage colony stimulating factor (GM-CSF) deficient mice develop a pulmonary alveolar proteinosis (PAP) syndrome which is corrected by the administration/expression of GM-CSF. These observations implicate GM-CSF in the pathogenesis of human PAP. We hypothesized that human PAP may involve an intrinsic cellular defect in monocytes/macrophages with an inability to produce GM-CSF and/or respond to GM-CSF. Thus, we investigated the cytokine responses to GM-CSF and LPS from peripheral blood monocytes and alveolar macrophages from patients with idiopathic PAP and healthy controls. Macrophage inflammatory protein-1-α (MIP) was measured from GM-CSF-stimulated cells and GM-CSF was measured from LPS-stimulated cells by ELISA. The MIP and GM-CSF production by monocytes and alveolar macrophages did not differ between PAP patients and healthy controls. Growth of the GM-CSF-dependent human myeloid cell line TF-1 was inhibited by serum from all patients studied (n = 10) and all patients had anti-GM-CSF antibody in their serum. The BAL from PAP patients had less detectable GM-CSF by ELISA than healthy controls (P = 0.05); in contrast, the inhibitory cytokine, interleukin-10 (IL-10), was increased in PAP compared to controls (P = 0.04). IL-10 is a potent inhibitor of LPS-stimulated GM-CSF production from healthy control alveolar macrophages. These studies are the first to demonstrate that circulating monocytes and alveolar macrophages from PAP patients are able to synthesize GM-CSF and respond to GM-CSF, suggesting no intrinsic abnormalities in GM-CSF signaling. In addition, these observations suggest that PAP in a subset of patients is the result of decreased availability of GM-CSF due to GM-CSF blocking activity and reduced GM-CSF production by IL-10.