Receptor (or element of a larger receptor complex) for C1q, mannose-binding lectin (MBL2) and pulmonary surfactant protein A (SPA). May mediate the enhancement of phagocytosis in monocytes and macrophages upon interaction with soluble defense collagens. May play a role in intercellular adhesion. Interacts with C1QBP; the association may represent a cell surface C1q receptor. (Microbial infection) Interacts with hepatitis virus C/HCV core protein. Highly expressed in endothelial cells, platelets, cells of myeloid origin, such as monocytes and neutrophils. Not expressed in cells of lymphoid origin. N- and O-glycosylated. Has been sometimes referred to as a collectin receptor. PubMed:11994479 reported that C1q is not a ligand for C1QR1.