The H4A3 monoclonal antibody specifically reacts with human CD107a, a heavily glycosylated type I membrane glycoprotein. CD107a is also known as Lysosomal-associated membrane protein 1 (LAMP-1) and is widely expressed intracellular antigen. It can be found on the surface of PHA-activated lymphocytes, activated platelets, cytotoxic T cells, NK cells, macrophages, epithelial cells, endothelial cells, and some tumor lines. CD107a is a ligand for E-selectin and galaptin and is reported to be involved in cell adhesion and tumor metastasis.