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Infect. Immun., Apr 1995, 1362-1368, Vol 63, No. 4
RL Dedrick and PJ Conlon
Blood-borne lipopolysaccharide (LPS) is thought to be a major inducer of
sepsis; however, it remains controversial whether an ongoing exposure to
LPS is required to maintain the underlying systemic inflammatory response.
To address this question, we have studied the expression of tumor necrosis
factor alpha (TNF-alpha), interleukin 1- beta (IL-1 beta), and the
procoagulant protein tissue factor induced by LPS ex vivo in whole human
blood. The addition of a 1-ng/ml bolus of LPS to blood rapidly induced mRNA
expression of all three genes. The mRNA levels peaked after 1 to 2 h,
depending on the gene, and then declined to baseline after approximately 5
h. The decline in mRNA expression was not caused by a loss of
responsiveness of the blood cells to LPS but rather correlated with the
neutralization of LPS inflammatory activity by plasma components.
Furthermore, administering a 1-ng/ml dose of LPS in six hourly aliquots of
167 pg/ml greatly prolonged the expression of mRNAs and induced a much
greater release of TNF-alpha and IL-1 beta protein than did a single bolus.
Dosing by repeated additions was more effective than a single bolus in
inducing secretion of TNF-alpha and IL-1 beta at LPS levels of < or = 10
ng/ml, which corresponded to the LPS neutralization capacity of plasma.
Finally, both mRNA expression and protein secretion induced by repeated
administration of LPS were rapidly reversed by the addition of the LPS-
neutralizing protein, bactericidal/permeability-increasing protein, even
after several hours of stimulation. These results indicate that continuous
or repeated exposure to LPS is required to maintain the expression of
inflammatory genes and that the activated state is rapidly reversed with
LPS neutralization.
Copyright © 1995, American Society for Microbiology
Prolonged expression of lipopolysaccharide (LPS)-induced inflammatory genes in whole blood requires continual exposure to LPS
Department of Biological Chemistry, XOMA Corporation, Berkeley, California 94710.
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