title: The influence of microenvironment on the cytotoxicity of TNF [symbol: see text] vitro.
abstract: OBJECTIVE
  Investigations were undertaken to study the influence of oxygen levels on tumor necrosis factor [symbol: see text] (TNF [symbol: see text] toxicity in vitro.
  
  
  METHODS
  The cell line used to assess the cytotoxicity of TNF [symbol: see text] the mouse fibroblast line L929. The cell line was incubated under conditions of 21%, 10%, 5% and 2% oxygen either before or during exposure to TNF [symbol: see text]. All incubations with TNF were for 24 h in the presence of 1 microgram/ml actinomycin D. Cell number was assessed immediately following treatment by a colormetric method.
  
  
  RESULTS
  By preincubating L929 cells under various oxygen conditions for 24 h prior to incubating with TNF [symbol: see text], we show that pretreatment does influence TNF [symbol: see text] cytotoxicity since up to 50 times more TNF [symbol: see text] is required to elicit the same survival level when L929 cells have been preincubated for 24 h at oxygen levels relevant to those in solid tumors, that is 2% rather than at 21%. A 24 h preincubation under an environment of 5% oxygen is not as effective at inducing resistance to TNF [symbol: see text] as incubation under 2% oxygen. However, this resistance could be significantly enhanced by lengthening the preincubation time. Indeed cells cultured for five passages under 5% oxygen levels are approximately 50 times more resistant to TNF [symbol: see text] than cells cultured under 21% oxygen. The resistance induced by conditions of reduced oxygen tension could be reversed over a 24 h period if cells were returned to an environment containing of reduced oxygen tension could be reversed over a 24 h period if cells were returned to an environment containing 21% oxygen.
  
  
  CONCLUSIONS
  The oxygen content of the cellular microenvironment has a profound influence on the cytotoxic action of TNF.
authors.affiliation: Vascular Targeting Group, CRC Gray Laboratory, Mount Vernon Hospital, Northwood, Middlesex, UK.
authors.forename: L E
authors.initials: LE
authors.lastname: Sampson
authors.forename: D J
authors.initials: DJ
authors.lastname: Chaplin
mesh_terms: D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D006801:Humans; D051379:Mice; D010100:Oxygen / Q000032:analysis; D011994:Recombinant Proteins / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D010100:Oxygen