The membrane-type collectin CL-P1 is a scavenger receptor on vascular endothelial cells

Collectins are a family of C-type lectins that have collagen-like sequences and carbohydrate recognition domains (CRD). They are involved in host defe nse through their ability to bind to carbohydrate antigens of microorganism s. The scavenger receptors type A and MARCO are classical type scavenger re ceptors that have internal collagen-like domains. Here we describe a new sc avenger receptor that is a membrane-type collectin from placenta (collectin placenta 1 (CL-P1)), which has a typical collectin collagen-like domain an d a CRD. The cDNA has an insert of about 2.2 kilobases coding for a protein containing 742 amino acid residues. The deduced amino acid sequence shows that CL-P1 is a type II membrane protein, has a coiled-coil region, a colla gen-like domain, and a CRD. It resembles type A scavenger receptors because the scavenger receptor cysteine-rich domain is replaced by a CRD. Northern analyses, reverse transcription-polymerase chain reaction, and immunohisto chemistry show that CL-P1 is expressed in vascular endothelial cells but no t in macrophages. By immunoblotting and flow cytometry CL-P1 appears to be a membrane glycoprotein of about 140 kDa in human umbilical vein or arteria l endothelial cells, placental membrane extracts, and CL-P1 transfected Chi nese hamster ovary cells. We found that CL-P1 can bind and phagocytose not only bacteria (Escherichia coli and Staphylococcus aureus) but also yeast ( Saccharomyces cerevisiae). Furthermore, it reacts with oxidized low density lipoprotein (OxLDL) but not with acetylated LDL (AcLDL). These binding act ivities are inhibited by polyanionic ligands (polyinosinic acid, polyguanyl ic acid, dextran sulfate) and OxLDL but not by polycationic ligands (polyad enylic acid or polycytidylic acid), LDL, or AcLDL. These results indicate t hat CL-P1 might play important roles in host defenses that are different fr om those of soluble collectins in innate immunity.