HIGH-DENSITY-LIPOPROTEINS CAN ACT AS CARRIERS OF GLYCOPHOSPHOINOSITOLLIPID-ANCHORED CD59 IN HUMAN PLASMA

CD59 (protectin) is a glycophosphoinositol (GPI) lipid-anchored inhibi tor of complement lysis that is expressed on the membranes of blood ce lls, endothelial cells, epithelial cells and cardiomyocytes. CD59 may be shed from cell surfaces, e.g. during cell injury, but when entering human plasma its fate is unknown. In this study we observed that radi olabelled lipid-anchored CD59, but not soluble urinary CD59 without an chor lipid, incorporated into high-density lipoprotein (HDL) particles when mixed with human serum and analysed by high resolution gel titra tion and anti-apoA-I affinity chromatography. Only a small proportion of CD59 entered the low-density lipoprotein (LDL) fraction. HDL partic les were capable of incorporating 25-42% of [I-125]CD59 that was prein serted into the membranes of rabbit erythrocytes (RaE) and transferred 7-14% of [I-125]CD59 back to RaE or to cultured human endothelial cel ls (EA.hy 926). Immunoaffinity purification and immunoblotting analysi s demonstrated that HDL isolated from normolipidemic human serum conta ined small amounts of CD59. These results suggest that HDL particles c ould be involved in the recycling of GPI lipid-anchored molecules rele ased from cell surfaces.