The H4B4 monoclonal antibody specifically binds to CD107b. CD107b is a heavily glycosylated, ~120 kDa type I transmembrane protein that is also known as lysosomal-associated membrane protein 2 (LAMP-2/LAMP2), LAMPB, or LGP110. CD107b is expressed in the lysosomal and endosomal membranes of most cell types where it may play a role in maintaining membrane integrity. CD107b is also expressed on the surface of activated platelets and lymphocytes, including T lymphocytes, e.g., degranulating CD8+ cytotoxic T cells. CD107b serves as a ligand for selectins, including E-selectin, and mediates cellular adhesion. CD107a/ LAMP-1 and CD107b /LAMP-2 are carriers for poly-N-acetyllactosamines, and display the sialyl Le[x] antigen. CD107b is likewise expressed on some tumor cells and cell lines, including U937 and KG1a, and may facilitate tumor metastases.