Background: Orthotopic liver transplantation (OLT) success is hampered by cellular damage elicited by ischemia-reperfusion injury (IRI) which lowers allograft survival. Research using murine models has shown liver IRI is mediated by both innate and adaptive immune responses. Pattern recognition receptors (PRRs) orchestrate the innate immune response thereby shaping subsequent adaptive immunity. PRRs in OLT are unique because portal circulation provides a continuous source of PRR ligands called pathogen-associated molecular patterns (PAMPs), and are therefore normally suppressed. However, the contribution of danger-associated molecular patterns (DAMPs), a class of PRR ligands released only upon hepatocyte injury, is still being assessed. Toll-like receptor 4 (TLR4) is a transmembrane PRR which mediates the activation of Kupffer cells in response to bacterial products translocated from the gut through the portal vein. TLR4 signaling contributes to hepatic inflammation and injury in many OLT recipients.

Aim: We hypothesize TLR4 is activated on innate cells via the DAMP high-mobility group protein B1 (HMGB1) released from injured hepatocytes, inducing proinflammatory cytokine production.

Methods/Results: To determine if IRI leads to the release of HMGB1 during and after reperfusion, we measured HMGB1 levels in the blood and initial liver flush (LF) from OLT recipients identified as IRI+ (n=26) or IRI- (n=25) by histopathology. HMGB1 was elevated in LF and returned to near pre-operative levels by 12h in most patients. We then investigated if HMGB1 released during OLT-IRI triggers innate myeloid cell activation through TLR4 receptor signaling. LF from IRI⁺ patients increased production of TNF-α from cultured human PBMCs and TLR4 signaling in HEK-Blue^TM hTLR4 transfected cells compared to IRI^– patients. Of note, all LF samples were positive for HMGB1, yet not all induced TNF-α production or TLR4 signaling, suggesting HMGB1 alone does not predict hepatocyte injury due to IRI. HMGB1 interaction with additional factors within the LF, such as the PAMP LPS, TLR4 cofactors CD14/MD-2, or redox status of HMGB1, may elicit innate cell activation.

Conclusion: Manipulation of innate immune response to IRI in the graft itself is a potential therapeutic strategy to improve OLT survival and clinical outcomes.

CITATION INFORMATION: Sosa R, Zarrinpar A, Lassman C, Busuttil R, Gjertson D, Kupiec-Weglinski J, Reed E. Innate Immune Signaling During Ischemia-Reperfusion Injury in Human Orthotopic Liver Transplantation. Am J Transplant. 2016;16 (suppl 3).

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