CD11c/CD18 ( p150/95, or complement receptor 4, CR4) is a monocyte/macrophage-enriched integrin that has been reported to bind to a variety of ligands. These include cell surface proteins (LPS, ICAM-1, ICAM-2, ICAM-4 and VCAM-1), extracellular matrix proteins (collagen I), and soluble ligands (iC3b, heparin and fibrinogen). It is expressed in macrophages, monocytes, granulocytes, subsets of T and B cells, and dendritic cells. CD11c functions as a cell surface receptor for numerous soluble factors and proteins. The interaction mediates leukocyte interactions with other cell types and is a signal transducing receptor. It is found primarily on myeloid cells, where its expression is regulated both during differentiation and during monocyte maturation into tissue macrophages.