Ischemic preconditioning in the liver is independent of regulatory T cell activity

NKT cells are important mediators of hepatic ischemia-reperfusion injury

Introduction

IRI results from the interruption then reinstatement of an organ's blood supply, and this poses a significant problem in liver transplantation and resectional surgery.

In this paper, we explore the role T cells play in the pathogenesis of this injury.

Materials & methods

We used an in vivo murine model of warm partial hepatic IRI, genetically-modified mice, in vivo antibody depletion, adoptive cell transfer and flow cytometry to determine which lymphocyte subsets contribute to pathology. Injury was assessed by measuring serum alanine aminotransfersase (ALT) and by histological examination of liver tissue sections.

Results

The absence of T cells (CD3εKO) is associated with significant protection from injury (p = 0.010). Through a strategy of antibody depletion it appears that NKT cells (p = 0.0025), rather than conventional T (CD4 + or CD8 +) (p = 0.11) cells that are the key mediators of injury.

Discussion

Our results indicate that tissue-resident NKT cells, but not other lymphocyte populations are responsible for the injury in hepatic IRI. Targeting the activation of NKT cells and/or their effector apparatus would be a novel approach in protecting the liver during transplantation and resection surgery; this may allow us to expand our current criteria for surgery.

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Hepatic IRI worsens outcome in liver transplantation.

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T cells are important in hepatic IRI.

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These are tissue-resident rather than recruited T cells.

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NKT, but not conventional T or NK cells, are key mediators of hepatic IRI.

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Targeting NKT activation or their effector apparatus may offer therapeutic potential.

An Evaluation of Ischaemic Preconditioning as a Method of Reducing Ischaemia Reperfusion Injury in Liver Surgery and Transplantation

Liver Ischaemia Reperfusion (IR) injury is a major cause of post-operative liver dysfunction, morbidity and mortality following liver resection surgery and transplantation. There are no proven therapies for IR injury in clinical practice and new approaches are required. Ischaemic Preconditioning (IPC) can be applied in both a direct and remote fashion and has been shown to ameliorate IR injury in small animal models. Its translation into clinical practice has been difficult, primarily by a lack of knowledge regarding the dominant protective mechanisms that it employs. A review of all current studies would suggest that IPC/RIPC relies on creating a small tissue injury resulting in the release of adenosine and l-arginine which act through the Adenosine receptors and the haem-oxygenase and endothelial nitric oxide synthase systems to reduce hepatocyte necrosis and improve the hepatic microcirculation post reperfusion. The next key step is to determine how long the stimulus requires to precondition humans to allow sufficient injury to occur to release the potential mediators. This would open the door to a new therapeutic chapter in this field.

High serum Aspartate transaminase levels on day 3 postliver transplantation correlates with graft and patient survival and would be a valid surrogate for outcome in liver transplantation clinical trials

Aspartate transaminase, a liver specific enzyme released into serum following acute liver injury, is used in experimental organ preservation studies as a measure of liver IR injury. Whether post-operative serum transaminases are a good indicator of IR injury and subsequent graft and patient survival in human liver transplantation remains controversial. A single centre prospectively collected liver transplant database was analysed for the period 1988-2012. All patients were followed up for 5 years or until graft failure. Transaminase levels on the 1st, 3rd and 7th post-operative days were correlated with the patient demographics, operative outcomes, post-operative complications and both graft and patient survival via a binary logistic regression analysis. Graft and patient survival at 3 months was 80.3% and 87.5%. AST levels on the 3rd (P = 0.005) and 7th (P = 0.001) post-operative days correlated with early graft loss. Patients were grouped by their AST level (day 3): <107iU, 107-1213iU, 1213-2744iU and >2744iU. The incidence of graft loss at 3 months was 10%, 12%. 27% and 59% and 1-year patient mortality was 12%, 14%, 27% and 62%. Day 3 AST levels correlate with patient and graft outcome post-liver transplantation and would be a suitable surrogate endpoint for clinical trials in liver transplantation.

Acute Liver Injury Is Independent of B Cells or Immunoglobulin M

Background & Aims

Acute liver injury is a clinically important pathology and results in the release of Danger Associated Molecular Patterns, which initiate an immune response. Withdrawal of the injurious agent and curtailing any pathogenic secondary immune response may allow spontaneous resolution of injury. The role B cells and Immunoglobulin M (IgM) play in acute liver injury is largely unknown and it was proposed that B cells and/or IgM would play a significant role in its pathogenesis.

Methods

Tissue from 3 models of experimental liver injury (ischemia-reperfusion injury, concanavalin A hepatitis and paracetamol-induced liver injury) and patients transplanted following paracetamol overdose were stained for evidence of IgM deposition. Mice deficient in B cells (and IgM) were used to dissect out the role B cells and/or IgM played in the development or resolution of injury. Serum transfer into mice lacking IgM was used to establish the role IgM plays in injury.

Results

Significant deposition of IgM was seen in the explanted livers of patients transplanted following paracetamol overdose as well as in 3 experimental models of acute liver injury (ischemia-reperfusion injury, concanavalin A hepatitis and paracetamol-induced liver injury). Serum transfer into IgM-deficient mice failed to reconstitute injury (p = 0.66), despite successful engraftment of IgM. Mice deficient in both T and B cells (RAG1-/-) mice (p<0.001), but not B cell deficient (μMT) mice (p = 0.93), were significantly protected from injury. Further interrogation with T cell deficient (CD3εKO) mice confirmed that the T cell component is a key mediator of sterile liver injury. Mice deficient in B cells and IgM mice did not have a significant delay in resolution following acute liver injury.

Discussion

IgM deposition appears to be common feature of both human and murine sterile liver injury. However, neither IgM nor B cells, play a significant role in the development of or resolution from acute liver injury. T cells appear to be key mediators of injury. In conclusion, the therapeutic targeting of IgM or B cells (e.g. with Rituximab) would have limited benefit in protecting patients from acute liver injury.

Impaired expansion of regulatory T cells in a neonatal thymectomy-induced autoimmune mouse model

Neonatal thymectomy in certain mouse strains is known to induce organ-specific autoimmunity due to impaired functions of T cells, including Foxp3(+) regulatory T (Treg) cells in the thymus. The precise mechanism underlying the induction of autoimmunity by neonatal thymectomy remains unclear. One possibility is that depletion of Treg cells breaks down peripheral tolerance. We examined the functions of Treg cells by using a murine Sjögren syndrome model of NFS/sld mice that underwent neonatal thymectomy. The ratio of Treg cells to effector memory phenotype T cells in thymectomy mice was significantly lower than that of nonthymectomy mice. In addition, in vitro induction of peripherally induced Treg cells by transforming growth factor-β (TGF-β) using naive T cells from Sjögren syndrome model mice was severely impaired. The mRNA expression of TGF-β receptor I and II and Smad3 and -4 in the TGF-β-induced signal transduction pathway of Treg cells in this Sjögren syndrome model were lower than those of control mice. In addition, Treg cells in this Sjögren syndrome model exhibited an interferon-γ-producing Th1-like phenotype that resembled effector T cells. In conclusion, these results suggest that abnormal expansion and differentiation of Treg cells and inflammatory cytokines produced by Treg cells contribute to the development of autoimmunity.

Near-term anti-CD25 monoclonal antibody administration protects murine liver from ischemia-reperfusion injury due to reduced numbers of CD4+ T cells

BACKGROUND

CD4(+) T cell is acknowledged as a key factor in the initiation phase of liver ischemia reperfusion injury. The purpose of current study is to demonstrate the effect of antecedent near-term anti-CD25 monoclonal antibody treatment on IR-induced liver injury by modulation of CD4(+) T cells.

METHODS

70% liver warm IR was induced in male C57BL/6 mice after anti-CD25 mAb or non-specific IgG administration. Liver function, histological damage, in vitro Proliferation, FACS, cytokine production, and immunofluorescence were assessed to evaluate the impact of antecedent near-term PC61 treatment on IR-induced liver injury.

RESULTS

After 70% liver ischemia, mice preconditioned with PC61 displayed significantly preserved liver function as characterized by less histological damage and reduced serum enzymes level. Mechanistic studies revealed that the protection effect of anti-CD25 mAb was associated with ameliorated intrahepatic inflammatory milieu and reduced CD4(+) T lymphocytes as manifested by the decrease of proinflammatory cytokine production (less expression of TNF-α, IFN-γ, IL-2, and IL-6) and the lower CD4/CD8 proportion.

CONCLUSIONS

Our results provide first line of evidence indicating that near-term treatment with anti-CD25 monoclonal antibody might provide protection for livers against IR-induced injury by reducing CD4(+) T cells, but not influencing functional Treg population. Therefore, our results demonstrate a potential function of anti-CD25 monoclonal antibody which was neglected in the past, and may be helpful in various clinical conditions, particularly in liver and kidney transplantations.

Regulatory T cells in AKI

Human AKI is manifested by inflammation, and an early feature in the pathogenesis is the accumulation of immune cells in the kidney. To understand the pathophysiology of AKI, results from animal models have shown a causal relation between the leukocyte activation and infiltration to the kidney after kidney ischemia-reperfusion. Blocking the activation or trafficking of proinflammatory leukocytes into the kidney preserves renal function and histologic integrity. In contrast, the anti-inflammatory lymphocytes called regulatory T cells have an intrinsic renal-protective function and may represent a novel therapeutic approach and/or target for pharmacological manipulation to ameliorate AKI. This review will highlight the recent insight gained into the role and mechanisms of regulatory T cells in AKI.