Potent CD14-mediated signalling of human leukocytes by Escherichia coli can be mediated by interaction of whole bacteria and host cells without extensive prior release of endotoxin.
How invading microorganisms are detected by the host has not been well defined. We have compared the abilities of Escherichia coli and lipopolysaccharides (LPS) purified from these bacteria to prime isolated neutrophils for phorbol myristate acetate-stimulated arachidonate release, to trigger respiratory burst in 1% blood, and to increase steady-state levels of tumor necrosis factor alpha mRNA in whole blood. In all three assays, bacteria were > or = 10-fold more potent than equivalent amounts of LPS and could trigger maximal cellular responses at ratios as low as one bacterium per 20 to 200 leukocytes. Both E. coli and LPS-triggered responses were enhanced by LPS-binding protein and inhibited by an anti-CD14 monoclonal antibody and the bactericidal/permeability-increasing protein (BPI). However, whereas O polysaccharide did not affect the potency of isolated LPS, intact E. coli carrying long-chain LPS (O111:B4) was less potent than rough E. coli (J5). Furthermore, material collected by filtration or centrifugation of bacteria incubated under conditions used to trigger arachidonate release or chemiluminescence was 5- or 30-fold less active, respectively, than whole bacterial suspensions. Extracellular BPI (not bound to bacteria) inhibited bacterial signalling, but BPI bound to bacteria was much more potent. Taken together, these findings indicate that E. coli cells can strongly signal their presence to human leukocytes not only by shedding LPS into surrounding fluids but also by exposing endotoxin at or near their surface during direct interaction with host cells.
Katz
S S
SS
Department of Microbiology, New York University School of Medicine, New York 10016, USA.
Chen
K
K
Chen
S
S
Doerfler
M E
ME
Elsbach
P
P
Weiss
J
J
D000209:Acute-Phase Proteins; D023181:Antimicrobial Cationic Peptides; D001422:Bacterial Adhesion; D001483:Base Sequence; D001770:Blood Bactericidal Activity; D001798:Blood Proteins / Q000502:physiology; D002352:Carrier Proteins / Q000502:physiology*; D002478:Cells, Cultured; D017931:DNA Primers / Q000737:chemistry; D004926:Escherichia coli / Q000276:immunology* / Q000472:pathogenicity; D006801:Humans; D018950:Lipopolysaccharide Receptors / Q000502:physiology*; D008070:Lipopolysaccharides / Q000276:immunology*; D008163:Luminescent Measurements; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D009504:Neutrophils / Q000276:immunology*; D019081:O Antigens / Q000276:immunology; D010741:Phospholipases A / Q000378:metabolism; D016897:Respiratory Burst; D015398:Signal Transduction; D000099231:Lipopolysaccharide-Binding Protein
D000209:Acute-Phase Proteins; D023181:Antimicrobial Cationic Peptides; D001798:Blood Proteins; D002352:Carrier Proteins; D017931:DNA Primers; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D019081:O Antigens; D010741:Phospholipases A; D000099231:Lipopolysaccharide-Binding Protein; C021623:bactericidal permeability increasing protein