Pulmonary alveolar proteinosis - Progress in the first 44 years

Pulmonary alveolar proteinosis is a rare clinical syndrome that was first described in 1958. Subsequently, over 240 case reports and small series have described at least 410 cases in the literature. Characterized by the alveolar accumulation of surfactant components with minimal interstitial inflammation or fibrosis, pulmonary alveolar proteinosis has a variable clinical course ranging from spontaneous resolution to death with pneumonia or respiratory failure. The most effective proven treatment-whole lung lavage-was described soon after the first recognition of this disease. In the last 8 years, there has been rapid progress toward elucidation of the molecular mechanisms underlying both the congenital and acquired forms of pulmonary alveolar proteinosis, following serendipitous discoveries in gene-targeted mice lacking granulocyte-macrophage colony-stimulating factor (GM-CSF). Impairment of surfactant clearance by alveolar macrophages as a result of inhibition of the action of GM-CSF by blocking autoantibodies may underlie many acquired cases, whereas congenital disease is most commonly attributable to mutations in surfactant protein genes but may also be caused by GM-CSF receptor defects. Therapy with GM-CSF has shown promise in approximately half of those acquired cases treated, but it is unsuccessful in congenital forms of the disease, consistent with the known differences in disease pathogenesis

Therapeutic efficacy of granulocyte-macrophage colony-stimulating factor in patients with idiopathic acquired alveolar proteinosis

Alveolar proteinosis (AP) is characterized by excessive surfactant accumulation, and most cases are of unknown etiology. Standard therapy for AP is whole-lung lavage, which may not correct the underlying defect. Because the hematopoietic cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) is required for normal surfactant homeostasis, we evaluated the therapeutic activity of CM-CSF in patients with idiopathic AP. Fourteen patients received 5 mug/kg/d CM-CSF for 6 to 12 wk with serial monitoring of the alveolar-arterial oxygen gradient ([A-a]Do(2)), diffusing capacity of carbon monoxide, computed tomographic scans, and exercise testing. Patients not responding to 5 mug/kg/d CM-CSF underwent stepwise dose escalation, and responding patients were retreated at disease recurrence. Stored pretreatment sera were assayed for CM-CSF-neutralizing autoantibodies. According to prospective criteria, five of 14 patients responded to 5 mug/kg/d GM-CSF, and one of four patients responded after dose escalation (20 mug/kg/d). The overall response rate was 43% (mean improvement in [A-a]Do(2) = 23.2 mm Hg). Responses lasted a median of 39 wk, and were reproducible with retreatment. CM-CSF was well-tolerated, with no late toxicity seen. The only treatment-related factor predictive of response was CM-CSF-induced eosinophilia (p = 0.01). Each of 12 patients tested had GM-CSF-neutralizing autoantibodies present in pretreatment serum. We conclude that GM-CSF has therapeutic activity in idiopathic AP, providing a potential alternative to whole-lung lavage

Emergency granulopoiesis

Neutrophils are a key cell type of the innate immune system. They are short-lived and need to be continuously generated in steady-state conditions from haematopoietic stem and progenitor cells in the bone marrow to ensure their immediate availability for the containment of invading pathogens. However, if microbial infection cannot be controlled locally, and consequently develops into a life-threatening condition, neutrophils are used up in large quantities and the haematopoietic system has to rapidly adapt to the increased demand by switching from steady-state to emergency granulopoiesis. This involves the markedly increased de novo production of neutrophils, which results from enhanced myeloid precursor cell proliferation in the bone marrow. In this Review, we discuss the molecular and cellular events that regulate emergency granulopoiesis, a process that is crucial for host surviva