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J. Exp. Med.,
Volume 186, Number 12, December 15, 1997 2051-2056
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From * The Rockefeller University, New York 10021; Gram-negative bacterial lipopolysaccharide (LPS) stimulates phagocytic leukocytes by interacting with the cell surface protein CD14. Cellular responses to LPS are markedly potentiated by
the LPS-binding protein (LBP), a lipid-transfer protein that binds LPS aggregates and transfers
LPS monomers to CD14. LBP also transfers LPS to lipoproteins, thereby promoting the neutralization of LPS. LBP present in normal plasma has been shown to enhance the LPS responsiveness of cells in vitro. The role of LBP in promoting LPS responsiveness in vivo was tested
in LBP-deficient mice produced by gene targeting in embryonic stem cells. Whole blood from
LBP-deficient animals was 1,000-fold less responsive to LPS as assessed by the release of tumor
necrosis factor (TNF)-
The Maxwell Finland Laboratory for Infectious
Diseases, Boston, Massachusetts 02118; § Boston University School of Medicine, Boston,
Massachusetts 02118;
XOMA Corporation, Berkeley, California 94710; ¶ Merck Research
Laboratories, Rahway, New Jersey 07065; ** University Medical Center Charité,
Humboldt-University, D-10117 Berlin, Germany
. Blood from gene-targeted mice was devoid of immunoreactive LBP,
essentially incapable of transferring LPS to CD14 in vitro, and failed to support cellular responses to LPS. These activities were restored by the addition of exogenous recombinant murine LBP to the plasma. Despite these striking in vitro findings, no significant differences in
TNF-
levels were observed in plasma from wild-type and LBP-deficient mice injected with
LPS. These data suggest the presence of an LBP-independent mechanism for responding to
LPS. These LBP knockout mice may provide a tool for discovering the nature of the presumed second mechanism for transferring LPS to responsive cells.
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