Genetic and antigenic studies and partial purification of a human serum lipoprotein carrying the Lp antigenic determinant

The TLp(a) genetic variant of human serum 3-lipoprotein was detected by Berg,' using immunodiffusion with heteroimmune precipitating antiserum. Genetic studies by various investigators2' 3 indicated that the presence or absence of the Lp(a) factor was under the control of a single, autosomal gene and that the frequencies of the Lpa and Lp genes were approximately 0.19 and 0.81, respectively. The Lp system is independent4 of the Ag system.5 Rittner and Wichmann6 suggested that a complex of Lp genes may give rise to quantitative differences in the concentration of Lp-lipoprotein in different individuals. Using heteroimmune ant,isera which distinguish the Lp (a+) and Lp (a-) phenotypes, we have developed a method for isolation and partial purification of the Lp-lipoprotein by density gradient ultracentrifugation. This method and preliminary genetic and antigenic studies are presented in this report. Materials and Methods.-(a) Preparation oJ antisera: Method 1: Rabbits were injected intravenously every third day for four we'eks with 1 ml of Lp(a+) serum. Blood was collected 7 days after the last injection. Method 2: A rabbit was given a 1-ml intraperitoneal injection of partially purified Lp-lipoprotein in complete Freund's adjuvant, followed by two 1-ml injections of Lp-lipoprotein without adjuvant at 2-week intervals. The rabbit was bled 1 week after the last injection. Anti-a- and anti-:-lipoprotein sera were prepared by the same procedure. Commercial rabbit antisera specific for humana%lipoprotein and :-lipoprotein (Certified B ood Donor Se'rvice Inc., Woodbury, N. Y.) were also used. (b) Absorption techniques: Antisera against Lp(a+) serum were absorbed with 1.5 vol of Lp(a-) serum at 4?C for 24 hr. Antiserum against partially purified Lp-lipoprotein