Studies on the Immunochemistry of Human Low Density Lipoproteins Utilizing an Hemagglutination Technique

Hemagglutination is a specific and sensitive technique for investigating the purity of lipoproteins and the immunologic relationships between low density lipoprotein fractions. The S(f) 10-400 and S(f) 3-9 lipoprotein fractions, isolated from human serum by dextran sulfate-density gradient centrifugation procedure and repurified by centrifugation appeared to contain only lipoprotein antigens since these fractions did not stimulate the production of antibodies against other serum proteins. Cross-absorption experiments with lipoproteins carried on "tanned" cells demonstrated that the S(f) 3-9 lipoprotein fraction contains all the antigenic components of the S(f) 10-400 lipoprotein fraction together with additional antigenic components not found in the S(f) 10-400 lipoprotein fraction. Thus S(f) 3-9 and S(f) 10-400 lipoprotein fractions are immunologically similar but not identical. Low density lipoproteins contain no antigens in common with the high density lipoproteins. An S(f) 3-9 antiserum can be used to detect both S(f) 3-9 and S(f) 10-400 antigens. The S(f) 3-9 lipoprotein fraction used as an antigen will detect antibodies against both S(f) 3-9 and S(f) 10-400 lipoprotein fractions. The S(f) 3-9 and S(f) 10-400 antisera did not contain immune antibodies against erythrocytes of the different blood groups or against sheep, guinea pig, dog, calf, pig, horse, and chicken erythrocytes. Normal subjects and subjects with recent myocardial infarctions had no circulating autoantibodies against the S(f) 3-9 and S(f) 10-400 lipoprotein fractions.