The CD93 antigen is a 652 amino acid cell-surface glycoprotein expressed by monocytes, neutrophils, platelets, microglia, and endothelial cells. CD93 was originally thought to be a putative receptor for the complement component C1q, a serum glycoprotein which plays an integral role in the activation of the classical pathway in response to immune complexes. As a result, in the literature the CD93 gene product has also been referred to as C1QR1 and C1qRp as well as MXRA4 (matrix-remodeling-associated protein 4). Recent studies suggest that the CD93 antigen plays a role in intercellular adhesion and in clearance of apoptotic cells. CD93 is a heavily O-glycosylated, type I transmembrane protein consisting of an N-terminal domain with homology to C-type Lectin domains, a tandem array of EGF-like domains, a single transmembrane domain and a short cytoplasmic tail.
