Evidence for a role of toll-like receptor 4 in development of chronic allograft rejection after cardiac transplantation.
BACKGROUND
Long-term success of cardiac transplantation is limited by various forms of graft rejection. The specific mechanisms initiating and controlling these highly specialized immune processes remain unclear so far.


METHODS
To investigate the role of innate immunity in the development of allograft rejection, we assessed toll-like receptor (TLR)4 expression and typical downstream effects of TLR signaling (B7-1, interleukin [IL]-12, tumor necrosis factor [TNF]-alpha) in circulating CD14+ monocytes in 38 transplant recipients 1 to 3 years and in 10 transplant recipients 6 to 10 years after transplantation and compared them with 20 healthy controls using reverse transcription polymerase chain reaction, flow cytometry, and enzyme-linked immunoadsorbent assay. The results were matched with endothelial function testing as an early clinical indicator of transplant vasculopathy early after transplantation.


RESULTS
Allograft endothelial dysfunction (ED) was defined as a compromised coronary flow reserve (CFVR) to acetylcholine (CFVR<2 in 13 of 38 transplant recipients). In these patients, mRNA transcript levels for TLR4 (P<0.05) and surface expression of TLR4 (P<0.005) and B7-1 (P<0.05) on circulating monocytes as well as secretion of IL-12 (P<0.02) and TNF-alpha (P<0.05) were significantly higher than in the remaining 25 patients without ED. Compared with the controls, recipients late after transplantation did not show significantly elevated levels of TLR4 or dependent mediators. These results were compared with mRNA levels in a mice model of acute and chronic rejection. Rejecting mice exhibited elevated mRNA levels for mTLR4 and mB7-1.


CONCLUSIONS
Our results suggest activation of innate immunity in heart-transplant recipients through TLR4 contributes to the development of chronic rejection after cardiac transplantation.
Methe
Heiko
H
Department of Cardiology, University Hospital Grosshadern, Ludwig-Maximilians University, Munich, Germany. hmethe@mit.edu
Zimmer
Edgar
E
Grimm
Cornelia
C
Nabauer
Michael
M
Koglin
Joerg
J
D000328:Adult; D000368:Aged; D000818:Animals; D018122:B7-1 Antigen / Q000032:analysis; D002908:Chronic Disease; D004730:Endothelium, Vascular / Q000502:physiology; D005260:Female; D006084:Graft Rejection / Q000209:etiology*; D016027:Heart Transplantation / Q000276:immunology*; D006801:Humans; D007113:Immunity, Innate; D018950:Lipopolysaccharide Receptors / Q000032:analysis; D008297:Male; D008562:Membrane Glycoproteins / Q000032:analysis / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008875:Middle Aged; D012333:RNA, Messenger / Q000032:analysis; D011956:Receptors, Cell Surface / Q000032:analysis / Q000502:physiology*; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D016042:Transplantation, Heterotopic; D014184:Transplantation, Homologous; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis
D018122:B7-1 Antigen; D018950:Lipopolysaccharide Receptors; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha