Submitted on February 17, 2006
Accepted on April 14, 2006
Surface Tension Influences Cell Shape and Phagocytosis
in Alveolar Macrophages
Hiroko Akei1, Jeffrey A Whitsett1, Michelle Buroker1, Takafumi Ninomiya2, Haruyuki Tatsumi2, Timothy E. Weaver1, and Machiko Ikegami1*
1 Pulmonary Biology, Cincinnati Children's Hosital Medical Center, Cincinnati, Ohio, United States
2 Department of Anatomy 1, Sapporo Medical University, Sapporo, Japan
* To whom correspondence should be addressed. E-mail: machiko.ikegami{at}cchmc.org.
The effect of surface tension on alveolar macrophage shape and phagocytosis was assessed in vivo and in vitro. Surface tension was regulated in vivo by conditionally expressing SP-B in Sftpb-/- mice. Increased surface tension and respiratory distress was produced by depletion of SP-B and was readily reversed by repletion of SP-B in vivo. Electron microscopy was used to demonstrate that alveolar macrophages were usually located beneath the surfactant film on the alveolar surfaces. Reduction of SP-B increased surface tension and resulted in flattening of alveolar macrophages on epithelial surfaces in vivo. Phagocytosis of intratracheally injected fluorescent microbeads by alveolar macrophages was decreased during SP-B deficiency and was restored by repletion of SP-B in vivo. Incubation of MH-S cells, a mouse macrophage cell line, with inactive surfactant caused cell flattening and decreased phagocytosis in vitro, findings that were reversed by the addition of sheep surfactant or phospholipid containing SP-B. SP-B controls surface tension by forming surfactant phospholipid film that regulates shape and non-specific phagocytic activity of alveolar macrophages on the alveolar surface.
