title: Acute allograft rejection in human liver transplant recipients is associated with signaling through toll-like receptor 4.
abstract: OBJECTIVE
  Toll-like receptor (TLR) signaling is a crucial step in initiating adaptive immune responses. In addition to recognizing endotoxin, TLR4 also recognizes endogenous ligands ('damage-associated structures'), which are released into the circulation in the peri-transplantation period. TLR2 to a lesser extent also recognizes these endogenous ligands. Multiple studies involving solid organ transplants demonstrate a clear association between TLR4 and allograft rejection. In the present study we assessed whether an association exists between TLR4 and TLR2-dependent responses and acute liver allograft rejection.
  
  
  METHODS
  The sample included 26 liver transplant recipients. Blood was taken pre-transplant and at multiple points over the first 14 days post-transplant. Monocytes were stimulated with TLR4 and TLR2 ligands, lipopolysaccharide and Pam-3-Cys, respectively. Monocyte TLR expression was determined using flow cytometry; enzyme-linked immunosorbent assays measured tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) production.
  
  
  RESULTS
  Nine (34.6%) patients experienced rejection. No differences existed in age, sex, disease or immunosuppression between rejectors and non-rejectors. Baseline TLR4 expression was significantly higher in rejectors (1.36 vs 1.02, P=0.01). There was no difference in TLR2 expression. In rejectors, baseline TLR4- and TLR2-dependent production of TNF-α and IL-6 was also significantly increased. Post-transplant, the two groups differed with regard to TLR4-dependent TNF-α production, with rejectors demonstrating progressive downregulation over the first week.
  
  
  CONCLUSIONS
  Prior to liver transplantation, patients who subsequently experience rejection demonstrate robust TLR4-dependent immune responses, which are not seen in those who do not reject. This supports the theory that damage-associated structures signaling through TLR4 may be responsible for the early activation of alloimmune T-cells, favoring allograft rejection.
authors.affiliation: Department of Medicine, The University of Melbourne, Austin Health, Melbourne, Victoria, Australia. adam.testro@austin.org.au
authors.forename: Adam G
authors.initials: AG
authors.lastname: Testro
authors.forename: Kumar
authors.initials: K
authors.lastname: Visvanathan
authors.forename: Narelle
authors.initials: N
authors.lastname: Skinner
authors.forename: Vesna
authors.initials: V
authors.lastname: Markovska
authors.forename: Peter
authors.initials: P
authors.lastname: Crowley
authors.forename: Peter W
authors.initials: PW
authors.lastname: Angus
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Gow
mesh_terms: D000208:Acute Disease; D000328:Adult; D002478:Cells, Cultured; D003545:Cysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005434:Flow Cytometry; D006084:Graft Rejection / Q000276:immunology*; D006801:Humans; D007113:Immunity, Innate / Q000187:drug effects; D015850:Interleukin-6 / Q000378:metabolism; D018950:Lipopolysaccharide Receptors / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008074:Lipoproteins / Q000494:pharmacology; D016031:Liver Transplantation / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D009000:Monocytes / Q000187:drug effects / Q000276:immunology*; D010865:Pilot Projects; D011446:Prospective Studies; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors; D051195:Toll-Like Receptor 2 / Q000819:agonists / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000819:agonists / Q000378:metabolism*; D014184:Transplantation, Homologous; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D015854:Up-Regulation; D014739:Victoria
chemical_list: C508600:IL6 protein, human; D015850:Interleukin-6; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D008074:Lipoproteins; C495342:TLR2 protein, human; C495345:TLR4 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; D003545:Cysteine