Function and regulation of leukocyte homing receptors

In vivo studies in the mid-1960s showed that lymphocytes home to various lymphoid compartments of the body in a tissue-specific manner. A central event in this process is adhesion of the leukocyte in the blood to specialized endothelial cells within the lymphoid organs. Leukocyte binding to the vascular endothelial cells involves many diverse adhesion molecules expressed by both cell types. Those adhesion molecules which contribute to the tissue specificity of the leukocyte-endothelial cell interactions are called "homing receptors." The study of homing receptors has progressed tremendously in recent years. The intent of this treatise is to review our current understanding of these molecules in the context of the lymphocyte and outline studies showing that these molecules have important functions for other leukocytes as well. A general overview of leukocyte-endothelial cell adhesion will not be given: the reader can easily find many excellent and up-to-date reviews of this subject in the literature. This review is an attempt to outline the major contributions to the identification and characterization of homing receptors. Apologies are extended for any oversights made.