IMMUNOCHEMICAL STUDIES ON HUMAN PLASMA L IPOPROTEINS*

Some years ago, a series of human serum lipoproteins, distinguishable by their hydrated densities and l ipid-protein ratios were recognized and isolated by ultracentr i fugal techniques (1). Certain of these l ipoproteins are invar iably present in human serum and the concentrat ions of these and of others can be quant i tat ive ly correlated with disease (2). No difference in the l ipoprotein distr ibution can be demonstrated between serum and plasma. The purpose of this invest igat ion was to obtain information about the immunochemical speci-ficity of some of the l ipoproteins. Methods Preparation of Lipoproteinsl.--All ipoproteins, unless it is otherwise indicated, were isolated from pooled plasma. The plasma was obtained from citrated blood which was rejected by the San Francisco Blood Bank because of blood clots, positive serologic tests for syphilis, or because 3 weeks or more had elapsed since it was drawn. Between 8 and 16 pints of blood were used per pool. Low density lipoproteins SI6 and SI13 were isolated by the method of Lindgren et al. (3). The ultracentrifugal homogeneity of similar preparations has been discussed (5). The hy-drated density of Ss6 lipoproteins i between 1.03 and 1.04 gm./ml, and that of Sjl3 lipo-proteins between 1.015 and 1.03 gm./ml. In Fig. 1 ultracentrifuge r cords of lot " density lipoprotein preparations are presented3 These lipoproteins were used as immunizing antigen