Lymphocyte homing receptors are cell adhesion molecules[1] expressed on lymphocyte cell membranes that recognize addressins on target tissues. Lymphocyte homing refers to adhesion of the circulating lymphocytes in blood to specialized endothelial cells within lymphoid organs.[2] These diverse tissue-specific adhesion molecules on lymphocytes (homing receptors) and on endothelial cells (vascular addressins) contribute to the development of specialized immune responses.
Free lymphocytes constantly recirculate in blood after their re-entry from lymphoid tissue, via lymphatic and thoracic ducts. This happens so that the full repertoire of antigenic specificities of lymphocytes is continuously represented throughout the body. Homing happens in tissue-specific manner—e.g. B lymphocytes migrate better to mucosa-associated lymphoid tissue (Peyer's patches), and T lymphocytes preferentially to the peripheral lymph nodes.[3]
The process of lymphocyte homing is deliberate, mediated by lymphocyte-endothelial recognition mechanisms that enable antigen-specific immune responses. Lymphocyte homing receptor control of organ-specific lymphocyte trafficking is thought to prevent autoreactivity in immune responses during B and T cell differentiation.[2] Recently, lymphocyte homing has become a topic of interest for investigation of treatments for multiple sclerosis, type 1 diabetes mellitus, leukemia, and psoriasis.[4]