Isolation and partial characterization of apolipoprotein D: a new protein moiety of the human plasma lipoprotein system.

Immunochemical studies of the major density classes established clearly the antigenic heterogeneity of the human plasma lipoprotein system [ 1 -3 ] . Recent chemical investigations have confirmed these earlier findings and demonstrated the presence of six antigenicalty distinct polypeptides designated as A-I,. A-II, C-I, C-II, C-Ill and LP-B* [4 -6 ] . An additional antigenic component detected predominantly in HDL [7-10] has been designated 'thin-line' polypeptide due to its characteristic appearance on double diffusion analyses of HDL with anti-HDL or anti-whole serum. Under such experimental conditions, the 'thinline' polypeptide appears as a characteristic thin precipitin line nearer the antigen well, while the major precipitin band due to LP-A is closer to the antibody well [9, 11]. The occurrence of 'thin-line' polypeptide has also been demonstrated in LDL [11] and