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Infection and Immunity, April 2000, p. 1953-1963, Vol. 68, No. 4
Sir William Dunn School of Pathology,
University of Oxford, Oxford OX1 3RE, United
Kingdom,1 and Department of
Molecular Biology and Medicine, Research Center for Advanced Science
and Technology, University of Tokyo, Tokyo 153, Japan2
Received 4 October 1999/Returned for modification 4 November
1999/Accepted 3 January 2000
Macrophage class A scavenger receptors (SR-AI and SR-AII)
contribute to host defense by binding polyanionic ligands such as lipopolysaccharide and lipoteichoic acid. SR-A knockout
(SR-A
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Macrophage Class A Scavenger Receptor-Mediated
Phagocytosis of Escherichia coli: Role of Cell
Heterogeneity, Microbial Strain, and Culture Conditions In
Vitro
/
) mice are more susceptible to endotoxic shock
and Listeria monocytogenes infection in vivo, possibly due
to decreased clearance of lipopolysaccharide and microorganisms,
respectively. We have used flow cytometry to analyze the role of SR-A
and other scavenger-like receptors in phagocytosis of bacteria in
vitro. Chinese hamster ovary cells stably transfected with human SR-A
bound Escherichia coli and Staphylococcus
aureus but ingested few organisms. Primary human monocyte-derived
macrophages (M
) bound and ingested E. coli more efficiently, and this was partially but selectively blocked by the
general SR inhibitor, poly(I). A specific and selective role for SR-A
was shown, since bone marrow culture-derived M
from SR-A
/
mice ingested fewer E. coli organisms
than did wild-type cells, while uptake of antibody-opsonized E. coli was unaffected. SR-A-dependent uptake of E. coli
varied with the bacterial strain; ingestion of DH5
and K1 by
SR-A
/
M
was reduced by 30 to 60% and 70 to 75%,
respectively. Phagocytosis and endocytosis via SR-A were markedly
down-modulated when M
were plated on serum-coated tissue culture
plastic compared to bacteriologic plastic, where cell adhesion is
mediated by SR-A and CR3, respectively. This paper demonstrates that
SR-A can bind and ingest bacteria directly, consistent with a role in
host defense in vivo, and highlights the importance of the source of
the M
, bacterial strain, and culture conditions on receptor function in vitro.
*
Corresponding author. Mailing address: Sir William Dunn
School of Pathology, University of Oxford, South Parks Rd., Oxford OX1
3RE, United Kingdom. Phone: 44-1865-275531. Fax: 44-1865-275515. E-mail: leanne.peiser{at}path.ox.ac.uk.
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