TUMOR NECROSIS FACTOR RELEASE FROM LIPOPOLYSACCHARIDE-STIMULATED HUMAN MONOCYTES: LIPOPOLYSACCHARIDE TOLERANCE IN VITRO Maja Mafic’ and Sanford R. Simon’,’ Human peripheral blood monocytes secrete tumor necrosis factor (TNF) in response to stimulation with bacterial lipopolysaccbaride (LPS). We have shown that isolated human monocytes pretreated with LPS for 24 h secrete lower levels of TNF on a second stimulation with LPS than monocytes that have been stimulated with a single dose of LPS either immediately after isolation or 24 h after isolation. The levels of TNF released by monocytes after the second stimulation with LPS are proportional to the LPS concentration over a range from 1 ng/mL to 10 pg/mL. Increasing concentrations of LPS used during the first 24-h stimulation induce greater suppression of TNF release after a second stimulation with LPS. After an initial stimulus of 10 pg/mL LPS, a second stimulation of monocytes even with 10 pg/mL LPS will result in TNF secretion similar to that of unstimulated cells. This in vitro tolerance apparently can be overcome by stimulating previously activated cells with phorbol myristate acetate. We have also shown that neither prostaglandin E, nor dexamethasone added during the initial stimulation with LPS had an effect on the subsequent reduction in TNF release on a second stimulation of monocytes with LPS. Copyright o 1991 by W.B. Saunders Company
In most mammals, gram-negative bacteria can cause a state of shock characterized by fever, hypotension, hypoglycemia, and multiorgan system injury and failure. This syndrome can be duplicated in animals by intravenous administration of lipopolysaccharide (LPS), an integral component of the of the outer membrane of gram-negative bacteria.’ Most of the effects of LPS seen in endotoxic shock are mediated through the mononuclear phagocyte-derived cytokine, tumor necrosis factor (TNF), also known as cachectin.’ TNF was first identified as a factor able to promote hemorrhagic necrosis in some transplanted tumors.3 Subsequently, TNF was recognized to have pleomorphic effects in host response to injury and infection.’ Passive immunization of mice against TNF/cachectin prevents endotoxin-induced death.4 All pathophysiological processes associated with LPS-induced shock can be reproduced
From
the Departments of Biochemistry and Cell Biology’ and Pathology: State University of New York, Stony Brook, NY. Address reprint requests to: Sanford R. Simon, Ph.D., Department of Pathology, SUNY at Stony Brook, Stony Brook, NY 117948691. Copyright 0 1991 by W.B. Saunders Company 1043-4666/91/0306-0009$5.00/O KEY WORDS: endotoxinicell
576
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by injection of TNF.5,6 LPS does not induce shock in the endotoxin-resistant C3H/Hej mouse in which TNF production is blocked due to a transcription defect.’ LPS is the most potent natural stimulus known to evoke TNF production by macrophages.8 Serum levels of TNF peak within 1 to 2 h after LPS stimulation.g-” In activated human monocytes, 1% of the total mRNA may code for TNF.5 It has been observed that maximal production of TNF mRNA occurs between 1 and 6 h after induction,‘2 but these levels subsequently begin to decrease at still later times.13 In supernatants from cultured LPS-stimulated monocytes, TNF begins to appear within 1 h and reaches its maximal level within 6 h of stimulation.14 Better insight into the mechanism of action of exogenous and endogenous factors involved in the regulation of TNF release is important not only for better understanding of endotoxic shock but also for developing strategies for therapeutic intervention in combatting autoimmune diseases and tumors. More recently, increasing evidence has been accumulating which points to the importance of the macrophage as a target for infection by human immunodeficiency virus and the role of TNF in viral proliferation.‘5-‘7 In animals exposed to nonlethal doses of endotoxin, a characteristic hyporesponsiveness to subsequent administration of endotoxin has been observed. CYTOKINE,
Vol. 3, No. 6 (November),
1991: pp 576-583
TNF
“Endotoxin tolerance” is characterized by an early hyporesponsiveness to a second exposure to endotoxin (
In most mammals, gram-negative bacteria can cause a state of shock characterized by fever, hypotension, hypoglycemia, and multiorgan system injury and failure. This syndrome can be duplicated in animals by intravenous administration of lipopolysaccharide (LPS), an integral component of the of the outer membrane of gram-negative bacteria.’ Most of the effects of LPS seen in endotoxic shock are mediated through the mononuclear phagocyte-derived cytokine, tumor necrosis factor (TNF), also known as cachectin.’ TNF was first identified as a factor able to promote hemorrhagic necrosis in some transplanted tumors.3 Subsequently, TNF was recognized to have pleomorphic effects in host response to injury and infection.’ Passive immunization of mice against TNF/cachectin prevents endotoxin-induced death.4 All pathophysiological processes associated with LPS-induced shock can be reproduced
From
the Departments of Biochemistry and Cell Biology’ and Pathology: State University of New York, Stony Brook, NY. Address reprint requests to: Sanford R. Simon, Ph.D., Department of Pathology, SUNY at Stony Brook, Stony Brook, NY 117948691. Copyright 0 1991 by W.B. Saunders Company 1043-4666/91/0306-0009$5.00/O KEY WORDS: endotoxinicell
576
tumor necrosis activation
factorlmonocytesllipopolysaccharidei
by injection of TNF.5,6 LPS does not induce shock in the endotoxin-resistant C3H/Hej mouse in which TNF production is blocked due to a transcription defect.’ LPS is the most potent natural stimulus known to evoke TNF production by macrophages.8 Serum levels of TNF peak within 1 to 2 h after LPS stimulation.g-” In activated human monocytes, 1% of the total mRNA may code for TNF.5 It has been observed that maximal production of TNF mRNA occurs between 1 and 6 h after induction,‘2 but these levels subsequently begin to decrease at still later times.13 In supernatants from cultured LPS-stimulated monocytes, TNF begins to appear within 1 h and reaches its maximal level within 6 h of stimulation.14 Better insight into the mechanism of action of exogenous and endogenous factors involved in the regulation of TNF release is important not only for better understanding of endotoxic shock but also for developing strategies for therapeutic intervention in combatting autoimmune diseases and tumors. More recently, increasing evidence has been accumulating which points to the importance of the macrophage as a target for infection by human immunodeficiency virus and the role of TNF in viral proliferation.‘5-‘7 In animals exposed to nonlethal doses of endotoxin, a characteristic hyporesponsiveness to subsequent administration of endotoxin has been observed. CYTOKINE,
Vol. 3, No. 6 (November),
1991: pp 576-583
TNF
“Endotoxin tolerance” is characterized by an early hyporesponsiveness to a second exposure to endotoxin (
