CD9

CD9, a multi-transmembrane glycoprotein and member of the Tetraspanin family, is expressed on the surface of many cells, including leukocytes, platelets, and endothelial cells. It interacts with various proteins and forms four-transmembrane protein-rich microdomains (TEMs), which regulate cell adhesion, movement, and signal transduction. CD9 is crucial for cell-cell interactions, immune responses, tumor metastasis, and sperm-egg fusion. Its expression in tumor cells may correlate with invasiveness and metastasis, and in immune cells, it influences immune synapse formation and extracellular vesicle function. CD9 also holds potential as a therapeutic target or biomarker for certain diseases.