Evaluation of monoclonal antibodies to human plasma low density lipoproteins. A requirement for lipids to maintain antigenic structure.
Human plasma low density lipoproteins (LDL) are composed of approximately 25% apoproteins and 75% lipids (w/w). Immunochemical properties of LDL were studied using monoclonal antibodies. BALB/c mice were immunized with LDL and the spleen cells from these mice were then fused with a non-immunoglobulin secreting myeloma cell line (F0). The clones producing desirable antibodies were selected to study the antigenic properties of LDL by enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay. First, it was found that the maximal binding of 125I-labeled LDL to polyvinyl chloride microtiter dishes was not temperature dependent. The binding affinity was high with a Ka value of approximately 1.9 X 10(10) M-1 while the monoclonal antibodies possessed an affinity to LDL of 5 X 10(8) M-1 which was 2 orders less than the affinity of LDL to the dishes. The former binding, once established, was irreversible as judged by a subsequent incubation with an excess of unlabeled LDL. The latter binding could be displaced by unlabeled LDL. Therefore, the ELISA technique offered a satisfactory approach to study the interaction between LDL and monoclonal antibodies. Removal of lipids from bound LDL by organic extraction resulted in a 50% loss of immunoreactivity, suggesting that the lipids of LDL are important in maintaining the antigenic structure of LDL. Since the apoprotein of LDL also constitutes approximately 40% of the mass (w/w) of very low density lipoproteins (VLDL), the immunoreactivity of VLDL assessed by LDL-monoclonal antibodies was also carried out. Removal of triglycerides from VLDL by lipoprotein lipase resulted in a substantial loss of immunoreactivity as determined by radioimmunoassay. These findings are consistent with the concept that lipids play a role in maintaining the integrity of the antigenic structure of LDL.
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D000915:Antibody Affinity; D000918:Antibody Specificity; D001053:Apolipoproteins / Q000378:metabolism; D001055:Apolipoproteins B; D001666:Binding Sites, Antibody; D001667:Binding, Competitive; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes; D005260:Female; D006801:Humans; D008066:Lipolysis; D008077:Lipoproteins, LDL / Q000097:blood / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C
D000911:Antibodies, Monoclonal; D001053:Apolipoproteins; D001055:Apolipoproteins B; D000939:Epitopes; D008077:Lipoproteins, LDL