The apolipoprotein A-I binding protein of placenta and the SP-40,40 protein of human blood are different proteins which both bind to apolipoprotein A-I.

A complement-associated protein SP-40,40, which is a normal constituent of human blood, binds to the main apoprotein, apoA-I, of high density lipoprotein (HDL). This protein, which is identical to apolipoprotein J, was compared to another apoA-I binding protein purified from human placenta. Immunologically the two apoA-I binding proteins are different.