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. An alternative name for CD11b is Integrin alpha M, or ITGAM. It associates non-covalently with CD18 to form the CR3 integrin. CR3 is highly expressed on leukocytes of the innate immune system, including neutrophils, monocytes and NK cells, but less so on macrophages. Antibody studies have shown CR3 to mediate inflammation by regulating leukocyte migration and adhesion, and to be involved in cell-mediated cytotoxicity, chemotaxis, and other immune processes. It is known to be involved in the complement system and phagocytosis, being a receptor for inactivated complement component 3b (iC3b). Two genomewide association studies conducted in 2008 showed single nucleotide polymorphisms of ITGAM to have a strong link to systemic lupus erythematosus. 
Recent CD11b antibody studies have shown specific functions for the alpha and beta subunits of CR3, with CD11b being directly involved with adhesion and cell migration. However, CD11b expression and, therefore, leukocyte migration is dependent upon the presence of CD18. We at Novus Biologicals have a large number of CD11b antibody products in our catalog, including microglia markers and partial recombinant proteins. We also have an extensive range of CD18 antibody reagents, for combined studies. Please contact our technical support department (technical@novusbio.com) for help choosing the best reagents for your experiment.
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