CD11b

By Jennifer Sokolowski, MD, PhD.

By Jennifer Sokolowski, MD, PhD.

By Jennifer Sokolowski, MD, PhD.

Integrins are transmembrane receptors composed of alpha and beta chains, where beta-integrins are mainly expressed in leukocytes. Leukocytes are white blood cells that act in the immune system to defend our body against foreign pathogens.

The protein CD11b has been implicated in the various adhesion-related interactions of cells such as monocytes, macrophages, natural killer (NK) cells, and granulocytes. It is part of a heterodimer that consists of CD11b and CD18. It also modulates the uptake of complement-coated particles within the cell. It is commonly used as a microglial marker in tissues derived from the nervous system.

Think B lymphocytes just produce antibodies? Think again! Although, of course, B cells are vital for the humoral immune response, many studies in recent years have begun to uncover antibody-independent actions of B cells: regulating T cells and thus also playing a part in cellular immunity. For example, B cell depletion therapy, a new treatment for autoimmune disorders, has been found to influence T cells in addition to antibody titers.

Pathogenic microorganisms utilize a variety of cell surface receptors to gain entry into host cells and to bypass the natural defense mechanisms. One of the most prominent receptors used in this fashion is the leukocyte adhesion receptor CD11b/c.

The beta-2 integrins, a family of four cell surface transmembrane glycoproteins expressed only on leukocytes, include CD11a/CD18, CD11b/CD18, CD11c/CD18, and CD11d/CD18. They consist of a common beta subunit (CD18) and homologous alpha subunits (CD11a-d) that bind noncovalently to form an alpha/beta heterodimer.

Microglia are the resident macrophages of the central nervous system, and the first line of immune defense. Pioneering antibody research in the 1990's identified the Integrin beta 2 protein (also called ITGB2, complement receptor 3, CR3, CD18, and Mac-1) as one of the key proteins in the recruitment of microglial cells. The ITGB2 subunit A is commonly called CD11b, and antibodies to this subunit are widely used as microglial markers.

What is CD11b?

CD11b is an integrin family member which pairs with CD18 to form the CR3 heterodimer. CD11b is expressed on the surface of many leukocytes including monocytes, neutrophils, natural killer cells, granulocytes and macrophages, as well as on 8% of spleen cells and 44% of bone marrow cells. Functionally, CD11b regulates leukocyte adhesion and migration to mediate the inflammatory response.