Complement receptor 3 and 4 (CR3 and CR4)

Complement receptors 3 (CR3) and 4 (CR4) are members of the beta-2 integrin family, primarily expressed on the surface of phagocytes such as macrophages, neutrophils, and dendritic cells (1.1.2, 1.4.4). CR3 is a heterodimer composed of CD11b and CD18, while CR4 consists of CD11c and CD18 (1.3.2, 1.4.3). These receptors play a critical role in the innate immune system by recognizing and binding to the iC3b fragment of the complement system, which opsonizes pathogens and apoptotic cells to facilitate their phagocytosis (1.1.1, 1.3.1). Beyond their role in clearance, CR3 and CR4 mediate leukocyte adhesion to the vascular endothelium and facilitate migration into tissues during inflammatory responses (1.2.1, 1.3.4). They are implicated in various pathological conditions, including chronic inflammation, autoimmune disorders like systemic lupus erythematosus, and neurodegenerative diseases where microglial CR3 contributes to synaptic pruning (1.2.4, 1.3.3). Therapeutic strategies targeting these receptors include monoclonal antibodies and small molecules designed to either inhibit their adhesive functions to reduce inflammation or activate them to promote the clearance of debris (1.2.3, 1.2.4). However, pharmacological modulation of CR3 and CR4 carries significant risks, such as increased susceptibility to infections and impaired wound healing due to the suppression of essential leukocyte functions (1.3.1, 1.5.4).

Other names

Mac-1p150,95CD11b/CD18CD11c/CD18Integrin alpha-M beta-2Integrin alpha-X beta-2ITGAM/ITGB2ITGAX/ITGB2Macrophage-1 antigen

Modulation of leukocyte adhesion, migration, and phagocytosis through antagonism or agonism of the integrin heterodimer subunits CD11b/CD18 and CD11c/CD18.