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© 2008 The American Thoracic Society doi: 10.1513/pats.200803-028HR Knowns and Unknowns of the Alveolus1 Yale University School of Medicine, New Haven, Connecticut; 2 North Carolina State University, Raleigh, North Carolina; 3 Mayo Clinic Scottsdale, Scottsdale, Arizona; 4 National Jewish Medical and Research Center, Denver, Colorado; and 5 Boston University, Boston, Massachusetts Correspondence and requests for reprints should be addressed to Erica L. Herzog, M.D., Ph.D., Yale University School of Medicine, Pulmonary and Critical Care Section, 300 Cedar Street, TAC 441-S, New Haven, CT 06510. E-mail: erica.lyndrup{at}yale.edu ABSTRACT Our current alveolar paradigm includes three highly specialized cell populations. Alveolar type I cells are flat, elongated cells that presumably enable gas exchange. Alveolar type II cells are small, cuboidal cells with metabolic, secretory, progenitor, and immunologic functions. Alveolar fibroblasts secrete extracellular matrix proteins that support alveolar structure. These cells work together to facilitate respiration. Many years of high-quality research have defined our understanding of alveolar biology. However, there is much to be determined about the factors controlling cellular phenotypes and crosstalk. Moreover, specific questions remain regarding origin, repopulation, and previously unrecognized functions of each cell. This article summarizes the current data for each cell type and highlights areas that would benefit from further investigation.
Key Words: alveolus pneumocyte fibroblast
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