title: Interleukin-17 enhances tumor necrosis factor alpha-induced synthesis of interleukins 1,6, and 8 in skin and synovial fibroblasts: a possible role as a "fine-tuning cytokine" in inflammation processes.
abstract: OBJECTIVE
  To compare the singular and combined effects of tumor necrosis factor alpha (TNFalpha), interleukin-1beta (IL-1beta), and IL-17 on messenger RNA (mRNA) expression, translation, and secretion of IL-6, IL-8, and IL-1beta in fibroblasts.
  
  
  METHODS
  Fibroblasts were stimulated with the relevant cytokine(s), pulse labeled with 35S-methionine, and the newly synthesized proteins were immunoprecipitated and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Gene expression was determined by Northern blot analysis. Secreted proteins were detected by enzyme-linked immunosorbent assay (ELISA).
  
  
  RESULTS
  IL-17 alone was a weaker stimulator of the transcription, translation, and secretion of other interleukins than was TNFalpha or IL-1beta. IL-17 (10 ng/ml) stimulated the expression of IL-6 mRNA by 1.3-fold, while TNFalpha (1 ng/ml) increased it by 3.7-fold, and IL-1beta (0.1 ng/ml) increased it by >30-fold. Unlike TNFalpha and IL-1beta, IL-17 hardly affected the expression of IL-8 and IL-1beta mRNA. Translation of IL-6 was 6.2 times greater with IL-17, but TNFalpha and IL-1beta stimulated it 28.9- and 174-fold, respectively. ELISA-measured secretion of IL-6 and IL-8 increased by 6.7 and 5.8 times, respectively, with IL-17, compared with 52 and 269 times with TNFalpha stimulation and 1,356 and 1,084 times with IL-1beta stimulation. Yet, when IL-17 was combined with other cytokines, these activities were stimulated much beyond the sum of the individual effects. The combination of IL-17 and TNFalpha induced the expression of IL-6 or IL-1beta mRNA 7 times more than their additive stimulation, and that of IL-8 mRNA 3.8 times more. Likewise, the secretion of IL-6 and IL-8 was 20 times and 5 times higher, respectively, than expected. This synergism started after 4 hours of combined treatment, and decayed after 24-48 hours regardless of cytokine presence. It could be blocked with anti-IL-17 but not with anti-IL-1.
  
  
  CONCLUSIONS
  Our findings suggest that the primary role of IL-17 is to synergize with TNFalpha and to fine-tune the inflammation process. Therefore, IL-17 may be a potential target for therapeutic intervention.
authors.affiliation: Institute of Allergy and Immunology, Assaf Harofeh Medical Center, Zerifin, Israel.
authors.forename: Y
authors.initials: Y
authors.lastname: Katz
authors.forename: O
authors.initials: O
authors.lastname: Nadiv
authors.forename: Y
authors.initials: Y
authors.lastname: Beer
mesh_terms: D000328:Adult; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004797:Enzyme-Linked Immunosorbent Assay; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects / Q000276:immunology; D006801:Humans; D007249:Inflammation / Q000188:drug therapy / Q000276:immunology / Q000378:metabolism; D007375:Interleukin-1 / Q000235:genetics* / Q000378:metabolism; D020381:Interleukin-17 / Q000494:pharmacology*; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism; D016209:Interleukin-8 / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D012867:Skin / Q000166:cytology; D013583:Synovial Membrane / Q000166:cytology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D007375:Interleukin-1; D020381:Interleukin-17; D015850:Interleukin-6; D016209:Interleukin-8; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha