A macrophage-suppressing 40-kD protein in a case of pulmonary alveolar proteinosis

Autoimmune Pulmonary Alveolar Proteinosis

Autoimmune pulmonary alveolar proteinosis (PAP) is a rare disease characterized by myeloid cell dysfunction, abnormal pulmonary surfactant accumulation, and innate immune deficiency. It has a prevalence of 7-10 per million; occurs in individuals of all races, geographic regions, sex, and socioeconomic status; and accounts for 90% of all patients with PAP syndrome. The most common presentation is dyspnea of insidious onset with or without cough, production of scant white and frothy sputum, and diffuse radiographic infiltrates in a previously healthy adult, but it can also occur in children as young as 3 years. Digital clubbing, fever, and hemoptysis are not typical, and the latter two indicate that intercurrent infection may be present. Low prevalence and nonspecific clinical, radiological, and laboratory findings commonly lead to misdiagnosis as pneumonia and substantially delay an accurate diagnosis. The clinical course, although variable, usually includes progressive hypoxemic respiratory insufficiency and, in some patients, secondary infections, pulmonary fibrosis, respiratory failure, and death. Two decades of research have raised autoimmune PAP from obscurity to a paradigm of molecular pathogenesis-based diagnostic and therapeutic development. Pathogenesis is driven by GM-CSF (granulocyte/macrophage colony-stimulating factor) autoantibodies, which are present at high concentrations in blood and tissues and form the basis of an accurate, commercially available diagnostic blood test with sensitivity and specificity of 100%. Although whole-lung lavage remains the first-line therapy, inhaled GM-CSF is a promising pharmacotherapeutic approach demonstrated in well-controlled trials to be safe, well tolerated, and efficacious. Research has established GM-CSF as a pulmonary regulatory molecule critical to surfactant homeostasis, alveolar stability, lung function, and host defense.

Pulmonary alveolar proteinosis: an overview for internists and hospital physicians

Pulmonary alveolar proteinosis (PAP) is a rare diffuse lung disease characterized by abnormal accumulation of surfactant-associated phospholipoproteinaceous material in the pulmonary alveoli. The clinical findings of slow-onset dyspnea or dyspnea on exertion and persistent dry cough are nonspecific; radiographic findings of "bat-wing configuration" and "crazy paving" appearance in high-resolution computed tomography are suggestive, but not diagnostic of PAP. The current gold standard of PAP diagnosis involves histopathological examination of alveolar specimens obtained from bronchoalveolar lavage and transbronchial lung biopsy. The characteristic histopathological features are intraalveolar periodic acid Schiff (PAS)-positive eosinophilic homogeneous material with well-preserved architecture ofalveolar septa. The current standard medical treatment of PAP involves the physical removal of the surfactant-associated phospholipoproteinaceous alveolar deposit by whole lung lavage, which causes clinical and radiological improvement in a majority of patients. Some patients have been successfully treated with recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF).

Pulmonary alveolar proteinosis

Pulmonary alveolar proteinosis (PAP) has been recognized for almost half a century. At least three separate pathophysiologic mechanisms may lead to the characteristic feature of PAP: the excessive accumulation of surfactant lipoprotein in pulmonary alveoli, with associated disturbance of pulmonary gas exchange. The prognosis for adult patients with PAP varies, but disease-specific survival rate exceeds 80% at 5 years. The survival rates for adult PAP patients seem to have increased progressively in the four decades since the initial clinical description of this condition. The last decade has brought new advances in laboratory and clinical research that are lifting a veil not only on PAP but also on general aspects of pulmonary surfactant biology and innate immune defense.

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.