Novel anti-cholesterol monoclonal immunoglobulin G antibodies as probes and potential modulators of membrane raft-dependent immune functions

Adrienn Bíró,László Cervenak,Andrea Balogh,András Lőrincz,Katalin Uray,Anna Horváth,László Romics,János Matkó,George Füst,Glória László

doi:10.1194/jlr.m600158-jlr200

Abstract

Natural autoantibodies against cholesterol are present in the sera of all healthy individuals; their function, production, and regulation, however, are still unclear. Here, we managed to produce two monoclonal anti-cholesterol antibodies (ACHAs) by immunizing mice with cholesterol-rich liposomes. The new ACHAs were specific to cholesterol and to some structurally closely related 3beta-hydroxyl sterols, and they reacted with human lipoproteins VLDL, LDL, and HDL. They bound, usually with low avidity, to live human or murine lymphocyte and monocyte-macrophage cell lines, which was enhanced substantially by a moderate papain digestion of the cell surface, removing some protruding extracellular protein domains. Cell-bound ACHAs strongly colocalized with markers of cholesterol-rich lipid rafts and caveolae at the cell surface and intracellularly with markers of the endoplasmic reticulum and Golgi complex. These data suggest that these IgG ACHAs may serve as probes of clustered cholesterol (e.g., different lipid rafts) in live cells and thus may also have immunomodulatory potential.

Highlights

Natural autoantibodies against cholesterol are present in the sera of all healthy individuals; their function, production, and regulation, are still unclear
Because cholesterol is an evolutionally conserved, abundant structural lipid in the plasma membrane of mammalian cells, it was tempting to speculate whether naturally occurring antibodies against cholesterol could bind to the surface of cells
Eotvos University, Budapest) and U937 (ATCC) human monocyte-macrophage cell lines were cultured in RPMI 1640 supplemented with 10% fetal calf serum

Summary

Introduction

Natural autoantibodies against cholesterol are present in the sera of all healthy individuals; their function, production, and regulation, are still unclear. Monoclonal anti-cholesterol antibodies (ACHAs) were first reported in 1988 by Swartz et al [1] after immunizing mice with cholesterol-containing liposomes, together with lipid A as adjuvant. They found cholesterol to be a surprisingly excellent immunogen, and murine monoclonal IgM-type complement-fixing antibodies to cholesterol were obtained [1]. Perl-Treves et al [4] developed and examined monoclonal IgM antibodies against cholesterol monohydrate crystals by implantation of cholesterol crystals in the spleen of mice This choice was motivated by the fact that cholesterol, in the living organism, may aggregate or precipitate in pathological situations as microcrystals (gallstones, atherosclerotic plaques). Balogh contributed to this work. 2 To whom correspondence should be addressed

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