Lipopolysaccharide-binding protein accelerates and augments Escherichia coli phagocytosis by alveolar macrophages.
BACKGROUND
The first step in bacterial clearance by leukocytes is attachment and phagocytosis. Although lipopolysaccharide-binding protein (LBP) is best known for potentiating LPS-induced cytokine production through a CD14-dependent pathway, recent studies suggest that LBP plays a critical role in clearance of gram-negative bacteria and is essential for survival after bacterial challenge. We therefore sought to examine LBP's effect on Escherichia coli phagocytosis by alveolar macrophages (AMs) and to determine if this effect is mediated through CD14.


METHODS
Phosphatidylinositol-specific phospholipase C (PIPLC)-treated and untreated rat AMs were incubated in the presence of increasing doses of recombinant LBP or negative control protein (choramphenicol acetyltransferase) prior to E. coli-FITC (Ec-F) BioParticle challenge. Phagocytosed bacteria were assayed by fluorescence measurement. A time course study was also performed.


RESULTS
LBP potentiated phagocytosis of Ec-F BioParticles by AMs in a dose-dependent fashion. Kinetic studies showed that LBP augmented Ec-F phagocytosis by 76% at 30 min. Treatment of AMs with PIPLC to remove CD14 resulted in only a partial decrease in LBP-mediated enhancement of phagocytosis.


CONCLUSIONS
These results clearly demonstrate that LBP plays an important role in enhancing Ec-F binding and phagocytosis in a time- and dose-dependent manner. This observed increase may not require the presence of CD14 as significant potentiation of phagocytosis still occurred after PIPLC treatment. We postulate that the LBP-mediated increase in Ec-F phagocytosis can occur in the absence of CD14 through the presence of another receptor.
Klein
R D
RD
Department of Surgery, University of Michigan, Ann Arbor, Michigan 48109-0666, USA. rdklein@umich.edu
Su
G L
GL
Schmidt
C
C
Aminlari
A
A
Steinstraesser
L
L
Alarcon
W H
WH
Zhang
H Y
HY
Wang
S C
SC
D000209:Acute-Phase Proteins; D000818:Animals; D001422:Bacterial Adhesion / Q000187:drug effects / Q000502:physiology; D002352:Carrier Proteins / Q000494:pharmacology*; D002478:Cells, Cultured; D004926:Escherichia coli; D016650:Fluorescein-5-isothiocyanate; D007700:Kinetics; D018950:Lipopolysaccharide Receptors / Q000502:physiology; D008070:Lipopolysaccharides / Q000494:pharmacology*; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000382:microbiology / Q000502:physiology*; D008297:Male; D008562:Membrane Glycoproteins; D010587:Phagocytosis / Q000187:drug effects / Q000502:physiology*; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism; D000099231:Lipopolysaccharide-Binding Protein
D000209:Acute-Phase Proteins; D002352:Carrier Proteins; D016650:Fluorescein-5-isothiocyanate; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D010738:Type C Phospholipases; D000099231:Lipopolysaccharide-Binding Protein