Lselectin

L-selectin, also known as CD62L and encoded by the SELL gene, is a cell adhesion molecule of the selectin family expressed on most leukocytes, including naive T cells, B cells, monocytes, and natural killer cells. It is especially prominent on circulating naive lymphocytes and is involved in their homeostatic trafficking to secondary lymphoid organs.

Structurally, L-selectin is a type I transmembrane glycoprotein. Its extracellular region includes a C-type lectin domain, an EGF-like domain, and a series of short consensus repeats, followed by a transmembrane segment and a short cytoplasmic tail that participates in intracellular signaling and cytoskeletal interactions. The cytoplasmic tail is subject to rapid regulatory changes that influence adhesion dynamics and receptor turnover.

Functionally, L-selectin mediates initial tethering and rolling of leukocytes on high endothelial venules (HEVs) within peripheral and mucosal lymph nodes. This rolling is mediated by ligands present on HEVs, collectively referred to as peripheral node addressins (PNAd), which include GlyCAM-1, CD34, and MAdCAM-1 in certain tissues. Proper L-selectin–PNAd interactions require specific post-translational glycosylation of ligands, including fucosylation and sulfation. Through this mechanism, L-selectin supports lymphocyte homing to lymph nodes and the recirculation of naive and central memory cells; its activity can influence the efficiency of immune surveillance.

Regulation and clinical relevance include rapid proteolytic shedding of L-selectin from the cell surface by metalloproteases such as ADAM family members, generating soluble L-selectin and reducing adhesive capacity. L-selectin expression and shedding are modulated during immune activation, inflammation, and various diseases, making it a potential biomarker of leukocyte activation and a target of anti-inflammatory strategies in some contexts.