Macrosialin, also known as CD68 and Gp11, is asingle-pass type I membrane protein which belongs to theLAMPfamily. CD68 is highly expressed by blood monocytesand tissue macrophages. It is also expressed in lymphocytes, fibroblasts andendothelial cells. CD68 is expressed in many tumor cell lines which could allowthem to attach to selectins on vascular endothelium,facilitating their dissemination to secondary sites. CD68 plays a role in phagocytic activities of tissue macrophages,both in intracellular lysosomal metabolism and extracellularcell-cell and cell-pathogen interactions. It is a commonly used marker formacrophages. However, a number of studies have shown that CD68 antibodies reactwith other hematopoietic and non-hematopoietic cell types, suggesting that CD68may not be a macrophage-specific antigen. CD68 binds to tissue- andorgan-specific lectins or selectins,allowing homing of macrophage subsets to particular sites. Rapid recirculationof CD68 from endosomes and lysosomesto the plasma membrane may allow macrophages to crawl over selectin-bearing substrates or other cells.

CD68 molecule