title: IL-17A alone weakly affects the transcriptome of intestinal epithelial cells but strongly modulates the TNF-α-induced expression of inflammatory mediators and inflammatory bowel disease susceptibility genes.
abstract: BACKGROUND
  In contrast to anti-TNF-α antibodies, anti-IL-17A antibodies lacked clinical efficacy in a trial with patients suffering from Crohn's disease. We therefore analyzed how IL-17A modulates the inflammatory response elicited by TNF-α in intestinal epithelial cells (IEC).
  
  
  METHODS
  Target mRNA levels in IEC and colonic biopsies were assessed by RNA microarray and quantitative real-time PCR. Signaling pathways were analyzed using receptor neutralization and pharmacological inhibitors. Target protein levels were determined by immunoblotting.
  
  
  RESULTS
  Microarray analysis demonstrated that IL-17A alone is a weak inducer of gene expression in IEC (29 regulated transcripts), but significantly affected the TNF-α-induced expression of 547 genes, with strong amplification of proinflammatory chemokines and cytokines (>200-fold increase of CCL20, CXCL1, and CXCL8). Interestingly, IL-17A differentially modulated the TNF-α-induced expression of several inflammatory bowel disease susceptibility genes in IEC (increase of JAK2 mRNA, decrease of FUT2, ICAM1, and LTB mRNA). Negative regulation of ICAM-1 by IL-17A was verified on protein level. The significance of these findings is emphasized by inflamed lesions of patients with inflammatory bowel disease demonstrating significant correlations (P < 0.01, Rho, 0.57-0.85) for JAK2, ICAM1, and LTB mRNA with IL17A and TNF mRNA.
  
  
  CONCLUSIONS
  Our study demonstrates the modulation of inflammatory bowel disease susceptibility gene mRNA in IEC as a novel important property of IL-17A. Given the weak impact of sole IL-17A stimulation on IEC target gene expression, our study provides an important explanation for the lack of clinical efficacy of sole IL-17A neutralization, but suggests a beneficial effect of combined IL-17A/TNF-α that is currently in clinical development.
authors.affiliation: *Department of Medicine II, and †Clinic for Preventive Dentistry and Parodontology, Ludwig-Maximilians-University, Munich, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Friedrich
authors.forename: Julia
authors.initials: J
authors.lastname: Diegelmann
authors.forename: Florian
authors.initials: F
authors.lastname: Beigel
authors.forename: Stephan
authors.initials: S
authors.lastname: Brand
mesh_terms: D015415:Biomarkers / Q000378:metabolism*; D015153:Blotting, Western; D016022:Case-Control Studies; D002478:Cells, Cultured; D004198:Disease Susceptibility; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006801:Humans; D007124:Immunoenzyme Techniques; D018836:Inflammation Mediators / Q000378:metabolism*; D015212:Inflammatory Bowel Diseases / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D020381:Interleukin-17 / Q000494:pharmacology*; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000166:cytology / Q000187:drug effects; D020411:Oligonucleotide Array Sequence Analysis; D011379:Prognosis; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D015415:Biomarkers; D018836:Inflammation Mediators; D020381:Interleukin-17; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha