© 2018 Elsevier Ltd All rights reserved. CR4 (p150/95, CD11c/CD18, x/2, ITGAX/ITGB2) is a member of the 2 integrin family and was first described in the early to mid-1980s. CR4 is primarily expressed on myeloid cells and is commonly used as one of the markers to identify dendritic cells. Similar to CR3, this complement receptor participates in leucocyte adhesion, activation and recruitment; cytokine production; host defence and phagocytosis. Primary ligands for CR4 include iC3b, ICAM-1, fibrinogen and VCAM-1. Expression of CR4 is regulated at the transcriptional level and through activation-induced release from intracellular granules, while its activity is controlled primarily through conformational changes and clustering at the cell surface. Unlike CR3, few functional studies of CR4 have been reported in different in vivo immune and inflammatory model systems. Those published to date suggest that this complement receptor is involved in host defence responses and can promote inflammatory processes in the vasculature, skin and central nervous system.