CD62L (L-selectin), a member of the selectin family of adhesion receptors (alongside CD62E and CD62P), is a transmembrane glycoprotein with a molecular weight ranging from 74-105 kDa, depending on cell type and glycosylation status. Structurally, it consists of an N-terminal C-type lectin domain critical for carbohydrate-mediated ligand binding, an epidermal growth factor (EGF)-like domain, two complement-binding protein-like short consensus repeat (SCR) domains, a spacer region, a transmembrane domain, and a short cytoplasmic tail. This multidomain architecture enables dynamic interactions with ligands such as GlyCAM-1, CD34, and MAdCAM-1 through calcium-dependent recognition of sialylated Lewis X moieties. Constitutively expressed on most leukocytes including naive T cells, neutrophils, monocytes, and eosinophils, CD62L mediates leukocyte tethering and rolling along vascular endothelia during inflammatory responses. It plays essential roles in lymphocyte homing to peripheral lymph nodes via high endothelial venules (HEVs) and facilitates neutrophil recruitment to inflamed tissues. Activation-induced proteolytic cleavage of its extracellular domain generates soluble CD62L, a regulatory mechanism that modulates leukocyte adhesion dynamics. While broadly expressed in circulating leukocytes, CD62L expression is notably absent on memory T cell subsets, reflecting its role in distinguishing naive and effector immune cell populations.
Programmed Death-Ligand 1 (PD-L1) is an immune checkpoint molecule expressed on antigen-presenting cells and various cancer cells, critically involved in modulating T-cell-mediated immune responses. Its interaction with programmed cell death protein 1 (PD-1) on activated T cells delivers inhibitory signals that suppress cytotoxic activity and promote immune tolerance-a mechanism exploited by malignancies to evade immune surveillance. Elevated PD-L1 expression has been documented across multiple tumor types including non-small cell lung carcinoma, melanoma, and gastrointestinal cancers, correlating with advanced disease progression and poorer prognostic outcomes.