CD11b, also known as integrin alpha-M (ITGAM) and CR3A, is a 170 kDa glycoprotein primarily expressed on myeloid cells such as granulocytes, monocytes, macrophages, dendritic cells, NK cells and subsets of T/ B cells. CD11b non-covalently associates with CD18 (ÃŽ²2 integrin) to form a heterodimer ÃŽ±MÃŽ²2, also called macrophage-1 antigen (Mac-1) or complement receptor 3 (CR3). Mac-1 plays an important role in cell-cell interaction by binding its ligands ICAM-1 (CD54), ICAM-2 (CD102), ICAM-4 (CD242), iC3b, and fibrinogen.