addressin

Addressin is a term used in immunology to describe endothelial cell surface molecules that act as tissue-specific ligands for homing receptors on lymphocytes. These ligands direct the trafficking of naive and memory lymphocytes to particular tissues by engaging receptors such as L-selectin and integrins on the lymphocytes, thereby helping to establish sites of immune surveillance and response.

In lymph nodes, high endothelial venules express peripheral node addressins (PNAd), a set of L-selectin ligands. The best-characterized PNAd ligands include glycosylated mucin-like proteins such as GlyCAM-1 and CD34, which display sulfated and sialylated carbohydrate structures that are recognized by L-selectin. In the gut, mucosal addressin cell adhesion molecule-1 (MAdCAM-1) is expressed on intestinal venules and binds the gut-homing integrin α4β7 on lymphocytes, directing trafficking to gut-associated lymphoid tissue. These interactions illustrate how addressins contribute to tissue-specific lymphocyte localization.

Historically, addressin referred to these ligands in a general sense; the term has become less common in favor of naming the specific molecules (for example PNAd and MAdCAM-1). Nevertheless, the concept remains central to understanding how vascular address patterns influence immune cell distribution.

Alterations in addressin expression or function can affect lymphocyte distribution and immune responses, and have been associated with inflammatory conditions and transplantation contexts.