Human Integrin  beta2/CD18 Biotinylated Antibody

Integrin alphaX beta2, also called CD11c/CD18, p150/95 or complement receptor type 4 (CR4), is one of four beta2 integrins. The non-covalent heterodimer of 150 kDa alphaX/CD11c and 95 kDa beta2/CD18 integrin subunits is expressed on macrophages, dendritic cells, and hairy cell leukemias, with lower amounts on other myeloid cells and activated B, NK, and some cytotoxic T cells (1-7). Like other integrins, alphaX beta2 has multiple activation states (3). In the presence of divalent cations and "inside-out" signaling, alphaX beta2 is fully active and extended. The alphaX vWFA or I-domain, which contains the adhesion sites, forms the N-terminal head region with the alphaX beta-propeller and the beta2 vWFA domain (1, 8). In the inactive state, the heterodimer flexes in the center at the alphaX thigh and calf domains and beta2 I-EGF domains, impeding access to adhesion sites (1). The 1088 aa human alphaX/CD11c ECD shares 70-76% amino acid (aa) sequence identity with mouse, rat, and canine alphaX while the 678 aa human beta2/CD18 ECD shares 81-83% aa sequence identity with mouse, rat, cow, dog, goat, sheep, and pig beta2. Potential alphaX isoforms containing 719 and 725 aa (as compared to full-length 1163 aa alphaX) lack the vWFA domain and the N-terminus. Active alphaX beta2 shares some adhesion partners with alphaM beta2/CD11b/CD18, including complement opsonin fragment iC3b, ICAMs, vWF, and fibrinogen, and is expressed on many of the same cells (4-11). However, alphaM beta2 activity is often constitutive, while alphaX beta2 activity requires cell activation (4-7). alphaX beta2 also binds osteopontin, Thy-1, plasminogen, heparin, and proteins with abnormally exposed acidic residues (11-16). The adhesion events are important for proliferation, degranulation, chemotactic migration, and phagocytosis of complement-opsonized particles (5, 6, 9, 11, 12, 16). Mutations of beta2, especially in the vWFA domain, cause leukocyte adhesion deficiency (LAD-1) and susceptibility to bacterial infections (17).