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. Marker for early multipotent hematopoietic precursor cells. May play a role in cell-cell interactions during hematopoietic and vascular development. Interacts with C1QBP; the association may represent a cell surface C1q receptor. Expressed in lung, heart and bone marrow. Expressed at lower level in ovary, whole embryo and fetal liver. Not detected in brain, adult liver or thymus. Highly expressed in peritoneal cavity and bone marrow macrophages. Not detected in epithelial cells. First detectable in day 9 embryos, in the endocardium and vascular endothelium in the anterior part of the embryo. Expression in endothelial cells, initially restricted to aorta, omphalomesenteric and umbilical arteries, later extends to subcardinal veins, intersomitic arteries and perineural vessels. On day 10, detectable in the entire embryo. N- and O-glycosylated.