Immunochemical evidence that human apoB differs when expressed in rodent versus human cells: Use of transgenic mice to simulate intra-species immunization for production of monoclonal antibodies

Xingyu Wang, Vinita Chauhan, Anh T. Nguyen, Joshua Schultz, Jean Davignon, Stephen G. Young, Jan Borén, Thomas L. Innerarity, Hui Rutai, and Ross W. Milne

Lipoprotein and Atherosclerosis Research Group, University of Ottawa Heart Institute, Ottawa, Ontario K1Y 4W7

Corresponding Author: rmilne{at}ottawaheart.ca

Low density lipoproteins (LDL) from human apolipoprotein B100 (apoB100) transgenic (HuBTg+/+) mice contain more triglyceride than LDL from normolipidemic subjects. To obtain monoclonal antibodies (mAbs) that could be used to elucidate the metabolic basis for the abnormal lipid composition of LDL in HuBTg+/+ mice and as conformational probes to study human LDL heterogeneity, we immunized HuBTg+/+ mice with LDL isolated from human plasma. One apoE-specific and four anti-apoB100-specific hybridomas were identified. Two mAbs, 2E1 and 3D11, recognized an epitope in the amino-terminal 689 residues of apoB in native apoB-containing lipoproteins (LpB) from human plasma or from the supernatant of human hepatoma HepG2 cells but did not react with LpB from HuBTg+/+ mice or LpB secreted by human apoB100-transfected rat McArdle 7777 hepatoma cells. 2E1 reacted weakly and 3D11 reacted strongly with apoB from HuBTg+/+ mice after sodium dodecyl sulfate polyacrylamide gel electrophoresis. The lack of expression of the 2E1 and 3D11 epitopes on native LpB from HuBTg+/+ mice did not solely reflect low hepatic lipase and cholesteryl ester transfer protein activities in mice or the abnormal lipid composition of the particles. Both epitopes were detected in all human plasma samples tested and in very low density lipoproteins, intermediate density lipoproteins, and LDL. The unexpected reactivity of these two mAbs suggests that human apoB expressed by rodent hepatocytes or hepatoma cells adopts a different conformation or undergoes different posttranslational modification than apoB expressed in human hepatocytes or hepatoma cells.

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