Leukocyte Interactions with Endothelium and Extracellular Matrix: The Role of Selectins and CD44

Publisher Summary Both neutrophils/macrophages and naive lymphocytes require a means to transmigrate the endothelial barrier. At sites of injury, leukocytes must adhere to endothelium stimulated by a variety of cytokines produced by local and infiltrating cells. In peripheral and mucosal lymph nodes, naive lymphocytes interact with specialized postcapillary structures known as “high endothelial venules” (HEVs) ( I ), so-called because of their plump appearance, in contrast to the typical flat endothelium in other organs. Subsequent to their adhesion to and penetration of the endothelial barrier, leukocytes require mechanisms that allow them to interact with the extracellular matrix (ECM) of a variety of organs. Each of these interactions is mediated by a number of leukocyte adhesion molecules that recognize specific ligands, or counter receptors, on endothelial cells and within the ECM. This chapter discusses two sets of molecules that regulate leukocyte trafficking by interacting with specific carbohydrate ligands: the selectins that mediate leukocyte–endothelial interactions; and CD44, a broadly expressed polymorphic cell surface molecule that plays a role in leukocyte communication with ECM.