Altered spleen architecture in Mpl^-/- c-Myb^Plt4/Plt4 mice. Histologic section of spleens from Mpl^-/- c-Myb^Plt3/Plt3 (lower panel) and control Mpl^-/- c-Myb^+/+ mice (upper panel) showing the increased network of collagen fibers in the red pulp (blue) and lymphoid follicles (arrows), which were were small and usually lacked germinal centers in mutant mice. Sections were photographed to Kodachrome ASA64 film (Eastman Kodak, Rochester, NY) using a Zeiss Axiophot microscope (Zeiss, Thornwood, NY) and camera with a Zeiss 20× objective lens, 0.60 numerical aperture. The scanned images were processed using Adobe Photoshop software (Adobe, San Jose, CA).