title: Evidence for IFN-gamma as a mediator of the lethality of endotoxin and tumor necrosis factor-alpha.
abstract: Current evidence indicates that endogenously produced peptide cytokines, most notably TNF-alpha and IL-1, mediate the lethality of experimental endotoxemia. Because circulating serum levels of IFN-gamma can be detected soon after TNF-alpha and IL-1 in response to endotoxin, we investigated the role of IFN-gamma in endotoxin and TNF-alpha lethality. Specific neutralizing antibodies to murine TNF-alpha (anti-TNF-alpha Ab) or murine IFN gamma (anti-IFN-gamma Ab) produced in our laboratory protected mice against the lethality of Escherichia coli endotoxin (LPS) administered 6 h later. Serum IFN-gamma levels 2 h after i.v. LPS were lower in mice treated with anti-TNF-alpha Ab compared to mice that received nonimmune IgG (median less than 2.5 vs 3.0 U/ml, P2 less than 0.05). In contrast, serum TNF-alpha levels 1 h after i.v. LPS peaked more than fourfold higher in mice treated with anti-IFN-gamma Ab compared to controls (median greater than 6400 vs 1405 pg/ml, p2 less than 0.05). Doses of TNF-alpha (300 micrograms/kg) and IFN-gamma (50,000 U) which were well tolerated when given individually were synergistically lethal in combination (0% lethality vs 100% lethality, P2 less than 0.001), and were associated with higher serum levels of IL-6 than with either cytokine alone. Anti-IFN-gamma Ab provided complete protection against exogenous human rTNF-alpha at the LD100 dose (1400 micrograms/kg, p2 less than 0.001), and in fact prevented lethality at doses four- to fivefold greater than the LD100 human rTNF-alpha (up to 6000 micrograms/kg). We conclude that IFN-gamma is synergistic with TNF-alpha, is essential for the lethality of LPS and TNF-alpha, and may have modulating effects on the negative control of serum levels of TNF-alpha after LPS in mice.
authors.affiliation: Surgical Metabolism Section, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
authors.forename: G M
authors.initials: GM
authors.lastname: Doherty
authors.forename: J R
authors.initials: JR
authors.lastname: Lange
authors.forename: H N
authors.initials: HN
authors.lastname: Langstein
authors.forename: H R
authors.initials: HR
authors.lastname: Alexander
authors.forename: C M
authors.initials: CM
authors.lastname: Buresh
authors.forename: J A
authors.initials: JA
authors.lastname: Norton
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology; D004731:Endotoxins / Q000633:toxicity*; D005260:Female; D007371:Interferon-gamma / Q000097:blood / Q000502:physiology*; D015850:Interleukin-6 / Q000097:blood; D008070:Lipopolysaccharides / Q000633:toxicity*; D051379:Mice; D008809:Mice, Inbred C3H; D011817:Rabbits; D014409:Tumor Necrosis Factor-alpha / Q000032:analysis / Q000633:toxicity*
chemical_list: D000906:Antibodies; D004731:Endotoxins; D015850:Interleukin-6; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma