Divergent response to LPS and bacteria in CD14-deficient murine macrophages.
Gram-negative bacteria and the LPS constituent of their outer membranes stimulate the release of inflammatory mediators believed to be responsible for the clinical manifestations of septic shock. The GPI-linked membrane protein, CD14, initiates the signaling cascade responsible for the induction of this inflammatory response by LPS. In this paper, we report the generation and characterization of CD14-null mice in which the entire coding region of CD14 was deleted. As expected, LPS failed to elicit TNF-alpha and IL-6 production in macrophages taken from these animals, and this loss in responsiveness is associated with impaired activation of both the NF-kappaB and the c-Jun N-terminal mitogen-activated protein kinase pathways. The binding and uptake of heat-killed Escherichia coli, measured by FACS analysis, did not differ between CD14-null and wild-type macrophages. However, in contrast to the findings with LPS, whole E. coli stimulated similar levels of TNF-alpha release from CD14-null and wild-type macrophages at a dose of 10 bioparticles per cell. This effect was dose dependent, and at lower bacterial concentrations CD14-deficient macrophages produced significantly less TNF-alpha than wild type. Approximately half of this CD14-independent response appeared to be mediated by CD11b/CD18, as demonstrated by receptor blockade using neutrophil inhibitory factor. An inhibitor of phagocytosis, cytochalasin B, abrogated the induction of TNF-alpha in CD14-deficient macrophages by E. coli. These data indicate that CD14 is essential for macrophage responses to free LPS, whereas other receptors, including CD11b/CD18, can compensate for the loss of CD14 in response to whole bacteria.
Moore
K J
KJ
Lipid Metabolism Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
Andersson
L P
LP
Ingalls
R R
RR
Monks
B G
BG
Li
R
R
Arnaout
M A
MA
Golenbock
D T
DT
Freeman
M W
MW
D000818:Animals; D001422:Bacterial Adhesion / Q000235:genetics / Q000276:immunology; D001425:Bacterial Outer Membrane Proteins / Q000502:physiology; D018821:CD18 Antigens / Q000502:physiology; D002460:Cell Line; D016207:Cytokines / Q000096:biosynthesis; D004926:Escherichia coli / Q000276:immunology* / Q000502:physiology; D005260:Female; D017353:Gene Deletion; D018950:Lipopolysaccharide Receptors / Q000097:blood / Q000235:genetics*; D008070:Lipopolysaccharides / Q000276:immunology*; D008262:Macrophage Activation / Q000235:genetics; D016177:Macrophage-1 Antigen / Q000502:physiology; D017737:Macrophages, Peritoneal / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016254:Mutagenesis, Insertional; D010587:Phagocytosis / Q000276:immunology; D015398:Signal Transduction / Q000276:immunology
D001425:Bacterial Outer Membrane Proteins; D018821:CD18 Antigens; D016207:Cytokines; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D016177:Macrophage-1 Antigen