On the cover: Spleen histopathology of C57BL/6 mice. Here, red pulp macrophages are detected by immunohistochemistry in a spleen section from a C57BL/6 mouse. Bound specific Abs are detected via an enzymatic reaction resulting in red staining. Sections were counterstained with hematoxylin. Raupach et al. Salmonella typhimurium strains carrying independent mutations display similar virulence phenotypes yet are controlled by distinct host defense mechanisms. 6133.)