The CD2 (HIT11) antibody recognizes a 50-kDa type-I single-chain transmembrane glycoprotein called LFA-2 (lymphocyte function associated antigen-2) or sheep red blood cell (SRBC) receptor. The CD2 antigen is e, Xenopus/Amphibian,pressed on 70-80% of peripheral blood lymphocytes and 80%-90% of thymocytes and NK cells. The primary ligand for CD2 is CD58 (LFA-3) despite binding to CD48, CD59 and CD15. The CD2 antigen plays a role in T cell signaling and in lymphocyte adhesion, and is an alternative pathway of T cell activation. There are two forms of CD2, a membrane form on cell surface and a soluble form in serum.