Plasma lipoproteins in liver disease. I. Immunologically distinct low-density lipoproteins in patients with biliary obstruction.

Sera from patients with extrahepatic biliary obstruction were found to have an abnormal lipoprotein (obstructive lipoprotein) which failed to react with antibodies to normal lipoproteins of d < 1.063. Preparations of this abnormal lipoprotein made by a combination of immunoprecipitation and multiple polyanion precipitations revealed a high content of free cholesterol (26%) and phospholipids (61%) but only trace amounts of cholesterol esters and triglycerides. Protein content varied from 13% to a corrected low of 5% when ultracentrifugation was also performed. Amino acid analyses of the latter preparations resembled that of lipoproteins of d < 1.006. The reasons underlying the apparent unreactivity of the abnormal lipoprotein were explored. No evidence could be found for soluble antigen-antibody complexes of gamma-globulin and the abnormal lipoprotein, nor for inhibition of antigen-antibody complex formation by serum factors. Purified preparations of obstructive lipoprotein did not react with antisera to high- or low-density lipoproteins prepared from normal sera. Moreover, rabbits immunized with the abnormal lipoproteins produced specific antibodies to this lipoprotein which reacted with a d < 1.006 lipoprotein in normal sera. All other lipoprotein fractions from normal sera were unreactive. It is not known whether this lipoprotein is abnormal by virtue of the presence of a unique peptide or because of secondary alterations in lipoprotein structure.