CD11b is also known as the integrin aM subunit and complement receptor CR3 and forms a heterodimer with CD18 (integrin b2 subunit). CD11b is expressed at variable levels on monocytes/macrophages,dendritic cells, granulocytes and their precursors and on NK cells. CD11b is a relatively late marker for ,myeloid differentiation and is undetectable on most myelomonocytic hematopoietic progenitor cells and more primitive cells, probably including pluripotent stem cells.