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(Arteriosclerosis, Thrombosis, and Vascular Biology. 1995;15:17-26.)
© 1995 American Heart Association, Inc.

Articles

Characterization of LDL and VLDL Binding Sites on Human Basophils and Mast Cells

Irene Virgolini; Shu-Ren Li; Qiong Yang; Elisabeth Koller; Wolfgang R. Sperr; Maria Leimer Peter Angelberger; Johannes Nimpf; Wolfgang Schneider; Peter Valent

From the Department of Nuclear Medicine (I.V., S.-R.L., Q.Y., M.L.), Department of Internal Medicine I, Division of Hematology and Hemostaseology (W.R.S., P.V.), Department of Clinical Pharmacology (I.V.), Department of Physiology (E.K.), and Institute for Molecular Biology (J.N., W.S.), University of Vienna, and the Department of Radiochemistry (P.A.), Research Center Seibersdorf, Austria.

Correspondence to Irene Virgolini, MD, Department of Nuclear Medicine, University of Vienna, AKH, Währinger Gürtel 18-20, Vienna, Austria.

Abstract Recent data suggest that basophils and mast cells play a potential role in the processing and accumulation of plasma lipoproteins. This study investigated the interactions of ¹¹¹In-low-density lipoprotein (LDL), ¹¹¹In-acetyl-LDL, and ¹¹¹In-very-low-density lipoprotein (VLDL) with purified primary human blood basophils, immortalized human basophils (KU812 cell line), and a human mast cell line, HMC-1. Binding sites for ¹¹¹In-LDL resolved into curvilinear Scatchard plots indicating two classes of specific binding sites on primary basophils (B_max1, 7404 sites/cell; K_d1, 1.9 nmol/L; B_max2, 39 611 sites/cell; K_d2, 29 nmol/L), on KU812 cells (B_max1, 8290±2690 sites/cell; K_d1, 2.4±0.6 nmol/L; B_max2, 46 470 sites/cell; K_d2, 33.4±7.8 nmol/L), and on HMC-1 cells (B_max1, 7840±360 sites/cell; K_d1, 1.8±0.8 nmol/L; B_max2, 61 450±9900 sites/cell; K_d2, 28.4±9.4 nmol/L). On KU812 cells, binding of ¹¹¹In-LDL was displaced by apolipoprotein (apo)-E–rich high-density lipoprotein (HDL) (IC₅₀, 14±6 nmol/L), LDL (IC₅₀, 29±11 nmol/L), VLDL (IC₅₀, 55±21 nmol/L), HDL₂ (IC₅₀, 420±140 nmol/L), and heparin (IC₅₀, 67±28 nmol/L), whereas no competition was produced by HDL, HDL₃, or acetyl-LDL (IC₅₀, >1 µmol/L). Western blot analysis using the monoclonal antibody C7 confirmed the presence of the LDL receptor on human basophils and HMC-1 cells. ¹¹¹In-acetyl-LDL binding sites (scavenger receptor) could be detected neither on human basophils nor on HMC-1 cells. ¹¹¹In-VLDL bound to a single class of high-affinity binding sites on primary basophils (B_max, 4320 sites/cell; K_d, 10 nmol/L), KU812 cells (B_max, 4020±840 sites/cell; K_d, 8±3 nmol/L), and HMC-1 cells (B_max, 6143±1866 sites/cell; K_d, 4±2 nmol/L). ¹¹¹In-VLDL binding was displaced by VLDL>LDL>apoE-rich HDL but not by heparin (IC₅₀ >1 mmol/L). In the presence of prostaglandin E₁, the number of ¹¹¹In-LDL receptors increased by 150% (P<.05) in the high-affinity range and by 170% (P<.01) in the low-affinity range, whereas the number of ¹¹¹In-VLDL binding sites remained unchanged. VLDL, LDL, HDL, and the subclasses HDL₂ and HDL₃ inhibited immunological histamine release by primary normal basophils (n=3) and mast cells (n=3). Our results provide evidence for the existence of LDL and VLDL binding sites on human basophils and HMC-1 mast cells. The exact biological and pathophysiological roles of these sites remain to be elucidated.

Key Words: lipoproteins • mast cells • histamine • arteriosclerosis

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