Impact of hepatic rearterialization on reperfusion injury and outcome after mouse liver transplantation

Comparing animal well-being between bile duct ligation models

A prevailing animal model currently used to study severe human diseases like obstructive cholestasis, primary biliary or sclerosing cholangitis, biliary atresia, and acute liver injury is the common bile duct ligation (cBDL). Modifications of this model include ligation of the left hepatic bile duct (pBDL) or ligation of the left bile duct with the corresponding left hepatic artery (pBDL+pAL). Both modifications induce cholestasis only in the left liver lobe. After induction of total or partial cholestasis in mice, the well-being of these animals was evaluated by assessing burrowing behavior, body weight, and a distress score. To compare the pathological features of these animal models, plasma levels of liver enzymes, bile acids, bilirubin, and within the liver tissue, necrosis, fibrosis, inflammation, as well as expression of genes involved in the synthesis or transport of bile acids were assessed. The survival rate of the animals and their well-being was comparable between pBDL+pAL and pBDL. However, surgical intervention by pBDL+pAL caused confluent necrosis and collagen depositions at the edge of necrotic tissue, whereas pBDL caused focal necrosis and fibrosis in between portal areas. Interestingly, pBDL animals had a higher survival rate and their well-being was significantly improved compared to cBDL animals. On day 14 after cBDL liver aspartate, as well as alanine aminotransferase, alkaline phosphatase, glutamate dehydrogenase, bile acids, and bilirubin were significantly elevated, but only glutamate dehydrogenase activity was increased after pBDL. Thus, pBDL may be primarily used to evaluate local features such as inflammation and fibrosis or regulation of genes involved in bile acid synthesis or transport but does not allow to study all systemic features of cholestasis. The pBDL model also has the advantage that fewer mice are needed, because of its high survival rate, and that the well-being of the animals is improved compared to the cBDL animal model.

Bile Duct Stent and Strain Selection Influences Long-Term Survival of Mouse Orthotopic Liver Transplantation

BACKGROUND

Although mouse orthotopic liver transplantation (MOLT) is considered the gold standard in basic liver transplantation research, only a handful of transplantation research centers can establish the MOLT model reliably and reproducibly. Besides techniques and instruments, some nontechnical factors determine the outcomes of MOLT. This study aimed to investigate the influence of different bile duct stents and mouse strains on the long-term survival rate of MOLT.

METHODS

Varying donor-recipient-bile duct stent combinations were applied to groups 1-6 (G1, B6J-B6J-PP tube; G2, B6J-C3H-PP tube; G3, B6J-B6J-1.5XPE10 tube; G4, B6N-C3H-1.5XPE10 tube; G5, B10-C3H-1.5XPE10 tube; G6, B6N-C3H-1.25XPE10 tube) to value their effect on the long-term survival of MOLT. Liver transplantation was performed based on these experimental designs. The survival state was monitored for 3 months.

RESULTS

The 1-month survival rate of G1 and G2 was 14.3% and 70%, respectively. The 1-month survival rate of G3 was 80%, which had no significant difference compared with G2. Both G4 and G5 had a favorable 1-month survival rate of 100%. The 3-month survival rate of G3, G4, and G5 was 0%, 25%, and 80%, respectively. G6 had the same 1-month and 3-month survival rates as G5, which were 100% and 80%.

CONCLUSIONS

This study suggests that C3H mice were better recipient selections than B6J mice. Donor strains and stent materials are also important factors for the long-term survival of MOLT. An ideal long-term survival of MOLT could be achieved by a rational donor-recipient-stent combination.

Protective Effect of Retrograde Reperfusion Against Hepatic Autophagy Impairment in Rat Liver Transplantation

The retrograde reperfusion (RTR) technique was introduced in orthotopic liver transplantation (OLT) to improve initial postoperative liver function, but the related mechanisms remain unexplained. We investigated the influences of different reperfusion sequences, including initial portal reperfusion (IPR) and RTR, on hepatic ischemia/reperfusion (I/R) injury and autophagic activity in a simplified rat orthotopic liver transplantation (ROLT) model.

METHODS

First, we established an ROLT model of male Sprague-Dawley rats to simulate either the IPR or RTR technique. The operative times and survival rates until postoperative day (POD) 7 were recorded. Liver enzyme levels, histologic damage, and in situ apoptosis were assessed. Second, we evaluated differences in the autophagic flux of liver grafts at 1, 2, and 6 hours after reperfusion between the IPR and RTR techniques. All experimental procedures involving animals were approved by the Institutional Animal Ethics Committee of the 900th Hospital of PLA.

RESULTS

In the first experiment, all animals survived to POD 7. In contrast to the IPR sequence, the RTR technique decreased the extent of graft I/R injury. In the second experiment, reperfusion markedly impaired the autophagic flux of ischemic liver grafts, but the RTR technique could alleviate and postpone the reduction in autophagy after I/R.

CONCLUSIONS

A feasible modified ROLT model with the cuff method was described and could flexibly simulate 2 reperfusion techniques: IPR and RTR. The use of the RTR sequence exhibited a protective effect against I/R injury and impairment of autophagy in liver grafts.

Details determining the success in establishing a mouse orthotopic liver transplantation model

Liver transplantation (LT) is currently the only effective treatment option for end-stage liver disease. The importance of animal models in transplantation is widely recognized among researchers. Because of the well-characterized mouse genome and the greater diversity and availability of both genetically modified animals and research reagents, mouse orthotopic LT (MOLT) has become an ideal model for the investigation of liver biology, tissue injury, regulation of alloimmunity and tolerance induction, and the pathogenesis of specific liver diseases. However, due to its complicated and technically demanding procedure, the model has merely been used by only a few research groups in the world for years. For a new learner, training lasting at least a couple of months or even years is required. Most of the investigators have emphasized the importance of elaborate techniques and dedicated instruments in establishing a MOLT model, but some details are often neglected. The nontechnical details are also significant, especially for researchers who have little experience in mouse microsurgery. Here, we review and summarize the crucial technical and nontechnical details in establishing the model of MOLT based on scientific articles and our experience in six aspects: animal selection, anesthesia, perioperative management, organ procurement, back-table preparation, and implantation surgery. We aim to enable research groups to shorten the learning curve and implement the mouse LT procedure with high technical success.

Hypothermic Oxygenated Machine Perfusion Alleviates Donation After Circulatory Death Liver Injury Through Regulating P-selectin-dependent and -independent Pathways in Mice

BACKGROUND

Hypothermic oxygenated machine perfusion (HOPE) has been shown to improve the quality of liver donation after circulatory death (DCD) compared to cold storage (CS). However, the mechanism by which HOPE works is unclear. In this study, a mouse liver HOPE system was developed to characterize the role of P-selectin in the protective effect of HOPE on DCD livers.

METHODS

A warm ischemia model of the liver and an isolated perfused liver system were established to determine a suitable flow rate for HOPE. Perfusate and tissue samples from wild-type and P-selectin knockout (KO) mice were used to determine liver function, apoptosis and necrosis rates, deoxyribonucleic acid injury and oxidative stress levels, leukocyte and endothelial cell activation, and inflammatory reactions.

RESULTS

A mouse liver HOPE system was successfully established. HOPE at flow rates between 0.1 and 0.5 mL/min · g were shown to have a protective effect on the DCD liver. P-selectin KO improved the quality of the DCD liver in the CS group, and reduction of P-selectin expression in the wild-type HOPE group had similar protective effects. Moreover, there was a reduction in the degree of oxidative stress and deoxyribonucleic acid injury in the P-selectin KO HOPE group compared with the P-selectin KO CS group.

CONCLUSIONS

We established a mouse HOPE system and determined its suitable flow. We also proved that P-selectin deficiency alleviated DCD liver injury. HOPE protected the DCD liver through regulating P-selectin-dependent and -independent pathways.

Hypothermic oxygenated machine perfusion alleviates liver injury in donation after circulatory death through activating autophagy in mice

Hypothermic oxygenated machine perfusion (HOPE) is a safe and reliable method that could alleviate liver injury in donation after circulatory death (DCD). This study focuses on the role of autophagy in HOPE's protective effect on DCD liver injury. A 30-minute warm ischemic liver model was established in mice. After 4 hours of cold storage (CS), 1 hour of hypothermic machine perfusion (HMP) with 100% O₂ or 100% N₂ was employed. During 2 hours of reperfusion, liver tissue and perfusate were collected to evaluate liver function, oxidative stress level, apoptosis, and necrosis. Western blotting was used to explore the level of autophagy. When the liver experienced warm ischemic injury, LC3B-II expression was significantly enhanced. Compared with the CS, HOPE induced lower release of AST and ALT, as well as lower oxidative stress levels, apoptosis, and necrosis cell numbers, and led to higher tissue ATP content. Meanwhile, expression of autophagy-related proteins, such as ULK1, Atg5, and LC3B-II, increased. When oxygen was completely replaced by nitrogen, the washout effect of HMP did not activate autophagy and did not relieve DCD liver injury. When the autophagy inhibitor 3-methyladenine was used in HOPE, the protective effect of HOPE was attenuated. In conclusion, DCD liver injury activated autophagy compared with healthy liver, while HOPE alleviated DCD liver injury by increasing autophagy levels further in this mouse model. However, HMP with 100% of N₂ had no beneficial effect on DCD liver injury or on autophagy levels compared with CS. The research on autophagy may provide a new strategy for alleviating DCD liver injury in clinical practice.

Re-Arterialized Rat Partial Liver Transplantation with an in vivo Vessel-Oriented 70% Hepatectomy

Split liver transplantation and living liver donor liver transplantation were developed in the clinic to utilize liver organs in a more efficient manner. To better understand the mechanism behind these surgical procedures, a rat partial liver transplantation (PLTx) model was established for relevant surgical studies. Because of the complexity of the rat PLTx model, a protocol with detailed descriptions is required. An article published previously reported a protocol in which ex vivo hepatectomy was used to achieve 50% rat PLTx. In contrast to this protocol, we introduced a re-arterialized PLTx with an in vivo 70% hepatectomy. An updated vessel-oriented hepatectomy was incorporated into the rat PLTx to refine the microsurgical procedure. The portal veins and hepatic arteries of the left lateral lobe and the median lobe were individually dissected and ligated before removal of the liver parenchyma, thereby decreasing the probability of bleeding in the remnant liver stump. Furthermore, an end-to-side vessel anastomosis between the common hepatic artery and the enlarged proper hepatic artery was introduced to re-arterialize the hepatic artery. By using this end-to-side vessel anastomosis technique, the diameter of the anastomosis was enlarged, thereby decreasing the difficulty of hand suture and maintaining a high rate of anastomotic patency. Moreover, the cuff anastomosis of the infrahepatic vena cava was slightly modified. A section of circumferential liver parenchyma around the vena cava of a recipient was preserved during cuff anastomosis to maintain the three-dimensional shape of the vascular lumen. This section of liver parenchyma was removed after completing the anastomosis. With this modification, the step involving placement of stay sutures was omitted, thereby further shortening the cuff anastomosis time. By using this protocol of rat PLTx, a low liver enzyme level, an intact liver lobular architecture and a high survival rate were achieved after microsurgery.

Efficient nonarterialized mouse liver transplantation using 3-dimensional-printed instruments

Because of the wide availability of genetically modified animals, mouse orthotopic liver transplantation is often preferred over rat liver transplantation. We present a simplified mouse liver transplantation technique and compare transplantation outcomes with versus without hepatic artery anastomosis. Instruments for liver implantation were designed and printed with a 3-dimensional (3D) printer. The suprahepatic vena cava anastomosis was performed with a 10-0 running suture. The vena porta and infrahepatic vena cava were joined on extraluminal cuffs, using the 3D-printed device for spatial alignment and stabilization. The hepatic artery was reconstructed in half of the recipients using intraluminal stents. Liver function tests (3, 7, and 28 days) and histology (7 and 28 days) were assessed after transplantation. We performed 22 consecutive syngeneic C57BL/6 mouse orthotopic liver transplantations. The median portal clamping time was 12.5 ± 1.5 minutes. The survival rate at 4 weeks was 100% for both arterialized and nonarterialized recipients (n = 7, 4 recipients of each group being killed for early histology at day 7). Liver function tests at 3, 7, and 28 days were similar between arterialized versus nonarterialized groups. Liver parenchyma demonstrated only irrelevant abnormalities in both groups. The proposed device allows for a shorter clamping time compared with the published literature. Using this technique, the artery does not need to be anastomosed, with no impact on graft and recipient outcomes. The device is available for 3D printing. Liver Transplantation 22 1688-1696 2016 AASLD.

Key Points in Establishing a Model of Mouse Liver Transplantation

The explosion of interest in research into the mouse genome and immune system has meant that the mouse orthotopic liver transplantation (MOLT) model has become a popular means of studying transplantation immunity, organ preservation, ischemia-reperfusion injury, and surgical techniques, among others. Although numerous modifications and refinements of surgical techniques have simplified the operation, the relatively short duration of postoperative survival after MOLT remains an obstacle to longer-term follow-up studies. Here, we summarize the scientific basis of MOLT and our experience improving and refining the model in six key areas: anesthesia, operative technique, perfusion and preservation of the liver, cuff technique, anhepatic time, and the value of rearterialization for the liver graft. We also compare the characteristics of different surgical techniques, and give recommendations for the best means of tailoring technique to the objectives of a study. In doing so, we aim to assist other investigators in establishing and perfecting the MOLT model in their routine research practice.

Orthotopic mouse liver transplantation to study liver biology and allograft tolerance

Orthotopic liver transplantation in the mouse is a powerful research tool that has led to important mechanistic insights into the regulation of hepatic injury, liver immunopathology, and transplant tolerance. However, it is a technically demanding surgical procedure. Setup of the orthotopic liver transplantation model comprises three main stages: surgery on the donor mouse; back-table preparation of the liver graft; and transplant of the liver into the recipient mouse. In this protocol, we describe our procedure in stepwise detail to allow efficient completion of both the donor and recipient operations. The protocol can result in consistently high technical success rates when performed by personnel experienced in the protocol. The technique can be completed in ∼2-3 h when performed by an individual who is well practiced in performing mouse transplantation in accordance with this protocol. We have achieved a perioperative survival rate close to 100%.

Comparison of Methods for the Reconstruction of the Hepatic Artery in Mouse Orthotopic Liver Transplantation

Background

The mouse model of arterialized orthotopic liver transplantation (AOLT) has played an important role in biomedical research. The available methods of sutured anastomosis for reconstruction of the hepatic artery are complicated, resulting in a high incidence of complications and failure. Therefore, we developed and evaluated a new model of AOLT in mice.

Materials and methods

Male inbred C57BL/6 mice were used in this study. A continuous suture approach was applied to connect the suprahepatic inferior vena cava (SHVC). The portal vein and infrahepatic inferior vena cava (IHVC) were connected according to the "two-cuff" method. The common bile duct was connected by a biliary stent. We used the stent (G3 group) or aortic trunk (G2 group) to reconstruct the hepatic artery. The patency of the hepatic artery was verified by transecting the artery near the graft after one week. The survival rate of the recipients and serum alanine aminotransferase (ALT) levels, hepatic pathologic alterations, apoptosis and necrosis were observed at one week postoperatively.

Results

The patency of the hepatic artery was verified in eight of ten mice in G3 and in six of ten mice in G2. The 7-day survival rate, extents of necrosis and apoptosis, and TGF-β levels were not significantly different among the three groups (P>0.05). However, the serum ALT levels and operation time were markedly lower in G3 compared with G2 or G1 (both P<0.05).

Conclusions

Reconstruction of the hepatic artery using a stent can be performed quickly with a high rate of patency. This model simplifies hepatic artery anastomosis and should be promoted in the field of biomedical research.

A review of various techniques of mouse liver transplantation

OBJECTIVES

Liver transplantation in a mouse model is a valuable tool for studying transplantation immunobiology and clinic-relevant issues. However, the successful establishment is highly technical and demanding, impeding its widespread use. Herein, the aims of this study were to review and analyze the various techniques of liver transplantation in mice to circumvent pitfalls and minimize the incidence of complications.

MATERIALS AND METHODS

A search of PubMed was made by using the key words "mouse liver transplantation" for articles published between January 1973 and July 2012. Of the 473 publications identified, 14 were shown to be closely associated with mouse liver transplantation and 4 articles discussed specific microsurgical techniques. Through reviewing these articles, a series of potential factors were collected and analyzed in combination with other murine transplantation models, which might influence successfully establishing a mouse model for liver transplantation.

RESULTS

A mouse liver transplantation model is feasible and practical for experimental studies. Mouse strain, type of anesthesia, type of perfusion and storage solution, and reconstruction of bile duct are relevant factors but not determinants for a successful transplantation. Cold and warm ischemia time should be less than 4.0 hours and 20 minutes, respectively.

CONCLUSIONS

The cuff preparation, reconstruction of the hepatic artery, and length of the anhepatic phase play critical roles in successfully establishing a liver transplantation model in mice.

Mechanisms of murine spontaneous liver transplant tolerance

Liver transplant is associated with the induction of peripheral immune tolerance. Liver allografts are accepted spontaneously in most combinations of mismatch in major histocompatibility complex, without any requirements for immunosuppression. Liver nonparenchymal cells (especially dendritic cells and Kupffer cells), costimulatory pathways, and activated T-cell apoptosis may contribute to the induction of liver tolerance. Therefore, liver tolerance is an active process that includes T-cell activation, proliferation, infiltration of the allograft, and T-cell apoptosis. Liver dendritic cells may modulate the amount of alloreactive T cells in liver graft recipients by expressing the coinhibitory molecule programmed death-ligand 1 and the immunosuppressive enzyme indoleamine 2,3-dioxygenase. Liver dendritic cells also may induce activated T-cell apoptosis and Foxp3+ regulatory T cells. Future studies may clarify the precise function of liver nonparenchymal cells, the interactions between programmed death-ligand 1 and other costimulatory signals, and the contribution of the liver microenvironment to the induction and expansion of Foxp 3 regulatory T cells.

New method of stent-facilitated arterial reconstruction for orthotopic mouse liver transplantation

BACKGROUND

Arterialized orthotopic liver transplantation (OLT) in the mouse mimics human liver transplantation physiologically and clinically. The present method of sutured anastomosis for reconstruction of the hepatic artery is complex and is associated with high incidence of complications and failure. This makes the endpoint assessment of using this complex model difficult because of the many variables of the technical aspect.

METHODS

A total of 14 pairs of donors and recipients from syngeneic male mice were used for arterialized OLT. The grafts were stored in University of Wisconsin solution at 4°C for less than 4 h, and the recipients underwent OLT using a two-cuff technique. The arterial reconstruction was facilitated by the use of a single stent connecting the donor liver artery segment to the recipient common hepatic artery.

RESULTS

All 14 recipients survived with the time for arterial reconstruction ranging from 4-10 min. Patency of the artery was confirmed by transecting the artery near the graft 2 and 14 d after transplantation. At day 2, five of the six arteries transected were patent and at day 14, seven of the remaining eight were patent for an overall patency rate of 85.7%.

CONCLUSIONS

The stent-facilitated arterial reconstruction can be done quickly with a high patency rate. This model expands the translational research efforts to address marginal livers such as steatotic livers.

Amphiregulin stimulates liver regeneration after small-for-size mouse liver transplantation

This study investigated whether amphiregulin (AR), a ligand of the epidermal growth factor receptor (EGFR), improves liver regeneration after small-for-size liver transplantation. Livers of male C57BL/6 mice were reduced to ~50% and ~30% of original sizes and transplanted. After transplantation, AR and AR mRNA increased in 50% but not in 30% grafts. 5-Bromodeoxyuridine (BrdU) labeling, proliferating cell nuclear antigen (PCNA) expression and mitotic index increased substantially in 50% but not 30% grafts. Hyperbilirubinemia and hypoalbuminemia occurred and survival decreased after transplantation of 30% but not 50% grafts. AR neutralizing antibody blunted regeneration in 50% grafts whereas AR injection (5 μg/mouse, iv) stimulated liver regeneration, improved liver function and increased survival after transplantation of 30% grafts. Phosphorylation of EGFR and its downstream signaling molecules Akt, mTOR, p70S6K, ERK and JNK increased markedly in 50% but not 30% grafts. AR stimulated EGFR phosphorylation and its downstream signaling pathways. EGFR inhibitor PD153035 suppressed regeneration of 50% grafts and largely abrogated stimulation of regeneration of 30% grafts by AR. AR also increased cyclin D1 and cyclin E expression in 30% grafts. Together, liver regeneration is suppressed in small-for-size grafts, as least in part, due to decreased AR formation. AR supplementation could be a promising therapy to stimulate regeneration of partial liver grafts.

Simultaneous orthotopic liver-kidney transplantation with hepatic arterial reconstitution in rats

Although combined liver-kidney (LK) transplantation has been effectively used in patients with end-stage liver disease and concurrent renal failure, a small animal model has been rarely described because of the technical difficulties. Herein, we have described techniques of a modified simultaneous LK transplantation model in rats. We have modified the techniques to perform 47 combined LK transplants in rats with reconstructed hepatic artery and renal vessels by a microvascular sleeve method and an end-to-end anastomosis technique without cross-clamping the vena cava and abdominal aorta, respectively. An average donor operation time was 34.4+/-6.3 min with cold ischemia times of 49.7+/-6.5 min and 61.3+/-4.1 min for liver and kidney grafts, respectively. The total time for recipient operation was 96.8+/-9.4 min with a 4-wk survival rate of 92.3% (36/39). A cumulative hepatic and renal arterial patency rate reached 90.2% (37/41). Normal grafts function tests were observed within the first week post-transplant, as well as normal histopathology studies of the 2 grafts in wk 4 post-transplant. Our method proves to be practical and may contribute to a wider use of the model in the studies of allograft rejection and tolerance induction during combined LK transplantation.

Exhaustive differentiation of alloreactive CD8+ T cells: critical for determination of graft acceptance or rejection

BACKGROUND

The precise role that CD8+ T cells play in the rejection and acceptance of different types of allograft is unclear and has been shown to vary between donor-recipient combinations.

METHODS

The response of adoptively transferred CD8+ T cells reactive to the donor alloantigen H2Kb was examined after transplantation of H2Kb liver, kidney, and heart grafts in mice.

RESULTS

After transfer of 6 x 10(6) alloreactive CD8+ T cells to T-cell depleted syngeneic mice spontaneous long-term acceptance of liver grafts was observed, whereas kidney and heart grafts were acutely rejected. Within 5 days of liver transplantation, we found that the entire H2Kb-reactive T-cell pool was stimulated to proliferate and differentiate into memory or effector cells that were detectable within lymphoid tissues as well as the liver graft itself. However, despite the generation of effector or memory T cells, liver allografts were accepted, which correlated with the exhaustion or deletion of such cells. In contrast, although activation and proliferation of H2Kb-reactive CD8+ T cells was observed after transplantation of heart or kidney grafts, unactivated, H2Kb-reactive CD8+ T cells were still present in the spleen even long term. Interestingly, differences in the effector function of liver and kidney graft infiltrating donor-reactive CD8+ T cells were not detected after adoptive transfer into immunodeficient mice, despite a reduction in Th1-type cytokines within liver grafts.

CONCLUSIONS

The rapid and extensive initial activation and differentiation of donor-reactive CD8+ T cells that occurs after liver transplantation leads to clonal exhaustion or deletion of the alloreactive CD8+ T-cell repertoire resulting in spontaneous tolerance induction.

Investigation into the onset and progression of transplant arteriosclerosis in a mice aortic retransplantation model

Long-term function of vascularized human organ grafts is often limited by transplant arteriosclerosis and can lead to graft failure. Here, we have analyzed the impact of an initial rejection episode on the later development of transplant arteriosclerosis. Following transplantation of allogeneic abdominal aortic segments in mice, aortic grafts were retransplanted into either immunodeficient or syngeneic recipients. Retransplantation of grafts from immunocompetent into immunodeficient mice as early as 2 days after the primary transplant resulted in intimal proliferation and obstruction of the graft lumen 30 days after the primary transplant. In contrast, retransplantation of the grafts into donor syngeneic B10 recipients within 7 days did not result in the development of transplant arteriosclerosis. These data suggest that the adaptive immune system can induce intimal proliferation by an initial lethal hit that is sustained by the innate response. However our data demonstrate that development of chronic rejection can be inhibited, in this case by retransplantation into a syngeneic host.

Kupffer cell heterogeneity: functional properties of bone marrow derived and sessile hepatic macrophages

Kupffer cells form a large intravascular macrophage bed in the liver sinusoids. The differentiation history and diversity of Kupffer cells is disputed; some studies argue that they are derived from blood monocytes, whereas others support a local origin from intrahepatic precursor cells. In the present study, we used both flow cytometry and immunohistochemistry to distinguish 2 subsets of Kupffer cells that were revealed in the context both of bone marrow transplantation and of orthotopic liver transplantation. One subset was radiosensitive and rapidly replaced from hematogenous precursors, whereas the other was relatively radioresistant and long-lived. Both were phagocytic but only the former population was recruited into inflammatory foci in response to CD8(+) T-cell activation. We propose the name "sessile" for the radioresistant Kupffer cells that do not participate in immunoinflammatory reactions. However, we found no evidence that these sessile Kupffer cells arise from immature intrahepatic precursors. Our conclusions resolve a long-standing controversy and explain how different experimental approaches may reveal one or both of these subsets.

Early intrahepatic accumulation of CD8+ T cells provides a source of effectors for nonhepatic immune responses

Interactions between the liver and CD8+ T cells can lead to tolerance, due in part to CD8+ T cell death. To test whether this was the case in an extrahepatic infection, we investigated the fate and effector capacity of intrahepatic CD8+ T cells during lung-restricted influenza infection in mice. Virus-specific T cells accumulated in livers without detectable intrahepatic presentation of viral Ags, and this accumulation was not restricted to the contraction phase, but was apparent as early as day 5. Intrahepatic influenza-specific cells were functionally similar to those recovered from the bronchioalveolar lavage, based on ex vivo cytokine production and specific target lysis. Both adoptive transfer of liver lymphocytes and orthotopic liver transplant of organs containing accumulated effector T cells revealed that activated CD8s from the liver were viable, expanded during reinfection, and generated a memory population that trafficked to lymphoid organs. Thus, intrahepatic CD8+ T cells re-enter circulation and generate functional memory, indicating that the liver does not uniformly incapacitate activated CD8+ T cells. Instead, it constitutes a substantial reservoir of usable Ag-specific effector CD8+ T cells involved in both acute and recall immune responses.

Cytotoxic T-cell response following mouse liver transplantation is independent of the initial site of T-cell priming

BACKGROUND

Liver transplantation in the mouse results in systemic induction of tolerance. The underlying mechanisms may also account for the persistence of chronic liver infections. It has therefore been hypothesized that antigen (Ag) presentation within the liver by nonprofessional antigen-presenting cells (APC) leads to incomplete T-cell activation, ultimately resulting in tolerance induction. We tested this hypothesis in an orthotopic mouse liver transplantation model.

METHODS

Mouse liver transplantation was used to manipulate antigen presentation in major histocompatibility complex (MHC)-disparate donor and recipient strains. The effect of restricted Ag presentation was studied using CD8+ T-cell receptor transgenic OT-I cells. Transgenic OT-I cells were activated by injection of their cognate peptide antigen SIINFEKL, which could be presented by the MHC class I of only one of the mouse strains. Depending on the strain combination, Ag presentation was restricted to either the transplanted liver itself, the recipient (excluding the transplanted liver), or systemically throughout the recipient. Extrahepatic Ag presentation by passenger leukocytes was eliminated by using donors of chimeric bone marrow.

RESULTS

OT-I cells encountering antigen only in the transplanted liver were activated, underwent extensive proliferation, and developed effector functions, based on IFN-gamma production and in vivo cytotoxicity assays. This T-cell activation and differentiation within the liver was comparable to animals with systemic Ag presentation and to animals with absent hepatic-parenchymal Ag presentation.

CONCLUSIONS

The restricted presentation of antigen in the liver showed no immunosuppressive effect on activation of CD8+ T cells. In contrast, the liver may be an excellent priming site for naive CD8+ T cells.

Immune role of hepatic TLR-4 revealed by orthotopic mouse liver transplantation

Activated CD8+ T cells migrate to the liver at the end of an immune response and go through apoptosis there, but this mechanism is impaired in mice lacking Toll-like receptor-4. This allowed us to test the importance of liver trapping in an ongoing immune response. In the absence of Toll-like receptor-4, reduced liver accumulation was associated with an increase in the circulating CD8+ T cell pool, more long-lived memory T cells and increased CD8+ T cell memory responses. Using experimental orthotopic liver transplantation, we showed that the effect of Toll-like receptor-4 on the formation of the CD8+ T cell memory resides in the liver.

CONCLUSION

These studies reveal a new function for the liver, which is to regulate the magnitude of T cell memory responses through a Toll-like receptor-4-dependent mechanism.

A microsurgical approach to hepatic and extrahepatic antigen presentation and its effects on the migration pattern of activated CD8+ T cells

CD8+T lymphocytes activated in peripheral lymphoid organs are believed to preferentially localize to the hepatic sinusoids, but the role of antigen in the process has been difficult to define. To create experimental mice in which the liver was unique in lacking the ability to present antigen, we adopted a novel microsurgical approach, in which the site of antigen presentation was restricted by orthotopic mouse liver transplantation of MHC Class I-disparate livers. We used two related mouse strains, of which the wild-type strain could present an injectable model antigen, while a mutant strain could not. By transplanting mutant-strain livers into wild type recipients, we were able to evaluate the absence of intrahepatic parenchymal antigen presentation on CD8+ T cell activation, differentiation, and migration. This illustrates that orthotopic liver transplantation is a powerful technique for addressing issues of antigen presentation.

Cellular and molecular mechanisms of liver tolerance

The liver exhibits a distinctive form of immune privilege, termed liver tolerance, in which orthotopic liver transplantation results in systemic donor-specific T-cell tolerance, while antigens introduced either into hepatocytes or via the portal vein also cause tolerance. Here we argue that the fundamental mechanism driving liver tolerance is likely to be the continuous exposure of diverse liver cell types to endotoxin, derived from the intestinal bacteria. This exposure promotes the expression of a set of cytokines, antigen-presenting molecules, and costimulatory signals that impose T-cell inactivation, partly via effects on liver antigen-presenting cells. The evidence favors clonal deletion mechanisms and is consistent with a role for regulatory T cells but does not support either anergy or immune deviation as important factors in liver tolerance.

CD25+CD4+ Regulatory T Cells Develop in Mice Not Only During Spontaneous Acceptance of Liver Allografts but Also After Acute Allograft Rejection

BACKGROUND

Liver grafts transplanted across a major histocompatibility barrier are accepted spontaneously and induce donor specific tolerance in some species. Here, we investigated whether liver allograft acceptance is characterized by, and depends upon, the presence of donor reactive CD25CD4 regulatory T cells.

METHODS

CD25 and CD25CD4 T cells, isolated from CBA. Ca (H2) recipients of C57BL/10 (B10; H2) liver and heart allografts 10 days after transplantation, were transferred into CBA. Rag1 mice to investigate their influence on skin allograft rejection mediated by CD45RBCD4 effector T Cells.

RESULTS

Fully allogeneic B10 liver allografts were spontaneously accepted by naive CBA.Ca recipient mice, whereas B10 cardiac allografts were acutely rejected (mean survival time=7 days). Strikingly, however, CD25CD4 T cells isolated from both liver and cardiac allograft recipients were able to prevent skin allograft rejection in this adoptive transfer model. Interestingly, CD25CD4 T cells isolated from liver graft recipients also showed suppressive potency upon adoptive transfer. Furthermore, depletion of CD25CD4 T cells in primary liver allograft recipients did not prevent the acceptance of a secondary donor-specific skin graft.

CONCLUSIONS

Our data provide evidence that the presence of CD25CD4 regulatory T cells is not a unique feature of allograft acceptance and is more likely the result of sustained exposure to donor alloantigens in vivo.

Complete differentiation of CD8+ T cells activated locally within the transplanted liver

The transplanted liver elicits systemic tolerance, and the underlying mechanism may also account for the persistence of liver infections, such as malaria and viral hepatitis. These phenomena have led to the hypothesis that antigen presentation within the liver is abortive, leading to T cell tolerance or apoptosis. Here we test this hypothesis in an optimized orthotopic liver transplantation model. In direct contradiction to this model, the liver itself induces full CD8+ T cell activation and differentiation. The effects of microchimerism were neutralized by bone marrow transplantation in the liver donor, and the lack of liver-derived antigen-presenting cells was documented by eight-color flow cytometry and by sensitive functional assays. We conclude that local antigen presentation cannot explain liver tolerance. On the contrary, the liver may be an excellent priming site for naive CD8+ T cells.

Inflammatory responses in a new mouse model of prolonged hepatic cold ischemia followed by arterialized orthotopic liver transplantation

The current models of liver ischemia/reperfusion injury (IRI) in mice are largely limited to a warm ischemic component. To investigate the mechanism of hepatic "cold" IRI, we developed and validated a new mouse model of prolonged cold preservation followed by syngeneic orthotopic liver transplantation (OLT). Two hundred and forty-three OLTs with or without rearterialization and preservation in University of Wisconsin solution at 4 degrees C were performed in Balb/c mice. The 14-day survivals in the nonarterialized OLT groups were 92% (11/12), 82% (9/11), and 8% (1/12) after 1-hour, 6-hour and 24-hour preservation, respectively. In contrast, hepatic artery reconstruction after 1-hour, 6-hour, and 24-hour preservation improved the outcome as evidenced by 2-week survival of 100% (12/12), 100% (10/10), and 33% (4/12), respectively, and diminished hepatocellular damage (serum alanine aminotransferase /histology). Moreover, 24-hour (but not 1-h) cold preservation of rearterialized OLTs increased hepatic CD4+ T-cell infiltration and proinflammatory cytokine (tumor necrosis factor-alpha, interleukin 2, interferon-gamma) production, as well as enhanced local apoptosis, and Toll-like receptor 4/caspase 3 expression. These cardinal features of hepatic IRI validate the model. In conclusion, we have developed and validated a new mouse model of IRI in which hepatic artery reconstruction was mandatory for long-term animal survival after prolonged (24-h) OLT preservation. With the availability of genetically manipulated mouse strains, this model should provide important insights into the mechanism of antigen-independent hepatic IRI and help design much needed refined therapeutic means to combat hepatic IRI in the clinics.

Safe time to warm ischemia and posttransplant survival of liver graft from non-heart-beating donors

AIM: To explore the dynamical changes of histology, histochemistry, energy metabolism, liver microcirculation, liver function and posttransplant survival of liver graft in rats under different warm ischemia times (WIT) and predict the maximum limitation of liver graft to warm ischemia.

METHODS: According to WIT, the rats were randomized into 7 groups, with WIT of 0, 10, 15, 20, 30, 45, 60 min, respectively. The recovery changes of above-mentioned indices were observed or measured after liver transplantation. The graft survival and postoperative complications in each subgroup were analyzed.

RESULTS: Liver graft injury was reversible and gradually resumed normal structure and function after reperfusion when WIT was less than 30 min. In terms of graft survival, there was no significant difference between subgroups within 30 min WIT. When WIT was prolonged to 45 min, the recipients’ long-term survival was severely insulted, and both function and histological structure of liver graft developed irreversible damage when WIT was prolonged to 60 min.

CONCLUSION: The present study indicates that rat liver graft can be safely subjected to warm ischemia within 30 min. The levels of ATP, energy charge, activities of glycogen, enzyme-histochemistry of liver graft and its recovery potency after reperfusion may serve as the important criteria to evaluate the quality of liver graft.