Apolipoprotein H, also known as beta-2-Glycoprotein1 (B2GP-1) is a plasma glycoprotein that circulates at a concentration of 200 ug/mL (4mM). B2GP-1 has been identified as a constituent of chylomicrons, very low density lipoproteins and high density lipoproteins in Human plasma. It has also been demonstrated to bind phospholipids, heparin and platelets where it can modulate the activity of adenylate (19percent). Although the precise function(s) are as yet unknown, B2GP-1 has been shown to interfere with blood coagulation by competitively binding to phospholipids exposed during cell activation or damage. Recent evidence also implicates B2GP-1 as a cofactor recognized by some anti-phospholipid antibodies present in autoimmune disorders such as systemic lupus erythematosus (SLE).