The 515 monoclonal antibody specifically binds to CD44. CD44 is an 80-95 kDa type I transmembrane glycoprotein, also known as Phagocytic glycoprotein-1 (Pgp-1), or Extracellular matrix receptor type III (ECMR-III). CD44 is a member of the hyaladherin family of hyaluronan-binding proteins, with structural similarities to selectins. CD44 is the receptor for hyaluronic acid. CD44 is expressed on leucocytes, erythrocytes, epithelial cells and weakly on platelets. CD44 has functional roles in cell migration, lymphocyte homing and adhesion during hematopoiesis and lymphocyte activation. The 515 monoclonal antibody can reportedly block cellular adhesion to hyaluronic acid.