- Apolipoprotein A-I is the major protein component of HDL. It is reported in this communication that apo A-I is a significant component of the protein layer adsorbed from blood or plasma to a variety of biomaterial surfaces, including hydrophobic and hvdrophilic polymers, liposomes, a heparinized surface, and a polysulfone hemodialyzer membrane. Evidence in support of this conclusion from SDS-PAGE and immunoblots of proteins eluted from the surfaces after blood or plasma contact is presented. Whether the presence of apo A-I on these surfaces results from the uptake of the free protein or HDL particles remains to be determined. It appears that apolipoprotein A-I and/or HDL deposition may be an important effect in blood-biomaterial interactions generally, and one that has been largely overlooked.