© 1997 American Heart Association, Inc.
Articles |
Evidence That Human Fc
Receptor IIA (CD32) Subtypes Are Not Receptors for Oxidized LDL
From the Veterans Administration Hospital in White River Junction, Vt, and the Department of Microbiology at Dartmouth Medical School, Lebanon, NH.
Correspondence to Peter Morganelli, PhD, Veterans Administration Hospital, Research 151, White River Junction, VT 05009. E-mail Peter.Morganelli{at}Dartmouth.edu
Abstract Several lines of evidence suggest that clearance of
oxidized LDL (oxLDL) immune complexes by macrophage IgG Fc
receptors (FcRs) plays a role in atherogenesis. OxLDL may also be
cleared directly by FcRs, as shown for murine FcRII-B2. In
humans, the homologous FcR is FcRIIA (CD32), which is abundantly
expressed on monocytes and macrophages and shares 60% sequence
identity with murine FcRII-B2. As murine FcRII-B2 and human
FcRIIA also share similar IgG ligand-binding properties, the purpose
of this study was to test the hypothesis that human CD32 is a receptor
for oxLDL. For these studies we used transfected Chinese hamster ovary
(CHO) cells, monocytes, and cell lines that functionally express either
of two FcRIIA subtypes (R131 or H131) and assayed binding or
degradation of several preparations of oxLDL. The integrity of all
oxLDL preparations was checked by studying their ability to react with
CHO cells expressing human type I scavenger receptors and by other
characteristics of lipoprotein oxidation. Although we showed that each
preparation of oxLDL could recognize class A or class B scavenger
receptors, we did not detect any differences in the binding or
degradation of any type of oxLDL preparation among control versus CHO
cell transfectants. Using monocytes that express FcRIIA and CD36, we
showed that the binding of oxLDL was inhibited by antibodies to CD36,
but not by FcRIIA antibodies. Thus, the data do not support the
hypothesis that human FcRIIA is by itself a receptor for oxLDL. We
conclude that human CD32 can mediate uptake of lipoprotein immune
complexes, but does not mediate uptake of oxLDL in the absence of
anti-oxLDL antibodies. OxLDL may interact with human mononuclear
phagocytes directly via other types of receptors, such as class A and
class B scavenger receptors or CD68.
Key Words: Fc receptors • scavenger receptors • CD36 • oxidized LDL
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