Cover: Four distinct subpopulations of lamellar bodies revealed on the basis of differential labeling with rab3D antibodies and phalloidin. Cryostat sections of fixed lung tissue were triple-labeled with the fluorescent F-actin probe, Alexa-568 phalloidin, polyclonal rab3D antiserum, and monoclonal antibody 3C9. Rab3D-immunoreactivity is shown in green, phalloidin-labeling is shown in red, and 3C9-immunoreactivity in blue. The overlays of the green, red, and blue channels are shown in the Merge panes. (A) Optical section through an AET-II cell showing a rab3D-positive, phalloidin-negative lamellar body (arrowhead). Note that the 3C9 staining reveals several lamellar bodies not labeled for rab3D or phalloidin. (B) An optical section through another AET-II cell reveals two phalloidin-labeled lamellar bodies (arrowheads); both are rab3D-negative. Note that the phalloidin-labeled lamellar bodies are in close proximity of the actin terminal web lining the apical plasma membrane. The cell also contained phalloidin-negative lamellar bodies, but they were present in separate optical sections. (C) This example shows, in one optical section, rab3D-positive, phalloidin-negative lamellar bodies (arrowheads), and a phalloidin-positive, rab3D-negative lamellar body (arrow). Other lamellar bodies are negative for both rab3D and phalloidin. Note that the rab3D-positive as well as the phalloidin-positive lamellar bodies are in close proximity of the apical plasma membrane. (D) Example of an optical section through an AET-II cell containing a lamellar body (arrowhead) that is positive for both rab3D and phalloidin. Lamellar bodies of this type belonged to the most infrequently encountered. Asterisks indicate the alveolar space. Scale bars represent 2 m. For more information see article by van Weeren and colleagues beginning on page 288.