RT Book, Section A1 Rochester, Carolyn L. A2 Grippi, Michael A. A2 Elias, Jack A. A2 Fishman, Jay A. A2 Kotloff, Robert M. A2 Pack, Allan I. A2 Senior, Robert M. A2 Siegel, Mark D. SR Print(0) ID 1122362270 T1 The Eosinophilic Pneumonias T2 Fishman's Pulmonary Diseases and Disorders, 5e YR 2015 FD 2015 PB McGraw-Hill Education PP New York, NY SN 978-0-07-179672-9 LK accessmedicine.mhmedical.com/content.aspx?aid=1122362270 RD 2024/03/28 AB The association between pulmonary infiltrates and eosinophilia was first identified by Loeffler in 1932. It is now recognized that the eosinophilic pneumonias are a heterogeneous group of disorders characterized by varying degrees of pulmonary parenchymal and/or blood eosinophilia.1 The precise role that eosinophils play in the pathogenesis of the different eosinophilic pneumonias is not clear. Normally, less than 2% of the leukocyte cell differential in bronchoalveolar lavage (BAL) are eosinophils. The presence of increased BAL and/or tissue eosinophils, and our knowledge of the biology of eosinophils (see Chapter 22) does, however, suggest that they play a variety of roles, including initiation, perpetuation, and amplification of tissue inflammation and injury. These effector functions are no doubt the result of the ability of the eosinophils to release numerous soluble mediators, including granule-derived proteins, arachidonic acid metabolites, proinflammatory cytokines, superoxide anions, metalloproteases, and hydroxyl radicals. The different roles of eosinophils in these disorders can be appreciated when comparisons are made of parasitic infections and disorders such as asthma or allergic bronchopulmonary aspergillosis (ABPA). In the former, eosinophils play a crucial role in eradicating the infectious pathogen; in the latter, the eosinophils accumulate in the lung as a result of immune hypersensitivity and are prominent mediators of tissue injury.