Immunologic cross-reactivity of the low density lipoprotein receptor from bovine adrenal cortex, human fibroblasts, canine liver and adrenal gland, and rat liver.

An antibody to the low density lipoprotein (LDL) receptor was prepared by immunization of rabbits with a partially purified receptor preparation from bovine adrenal cortex. Immunoglobulin G (IgG) isolated from the serum of immunized rabbits blocked the binding of 125I-LDL to intact bovine adrenal membranes as well as to the partially purified bovine adrenal LDL receptor. The anti-receptor IgG also blocked the binding, uptake, and degradation of 125I-LDL by monolayers of human fibroblasts and thus prevented the LDL-mediated suppression of 3-hydroxy-3-methylglutaryl coenzyme A reductase. A monovalent Fab fragment of th anti-receptor IgG retained the ability to inhibit LDL receptors of partially purified bovine adrenal cortex and monolayers of human fibroblasts. By immunofluorescence staining, the anti-receptor IgG was shown to bind to normal fibroblasts in discrete foci that were linearly arranged on the cell surface. No such foci were seen on fibroblasts from a patient with the receptor-negative form of homozygous familial hypercholesterolemia. The rabbit anti-receptor IgG also blocked the binding of 125I-LDL to membranes from dog and rat liver, but it did not prevent LDL binding to rabbit adrenal membranes or rabbit fibroblasts. The immunologic cross-reactivity of LDL receptors from bovine adrenal cortex, human fibroblasts, canine liver and adrenal gland, and rat liver indicates that the structure of this receptor has been widely conserved among animal species and tissues.