Role of toll-like receptors in liver transplantation

Incidence of opportunistic viral infections in hepatitis C virus nucleic acid test negative recipients of kidneys from hepatitis C virus nucleic acid test positive donors

BACKGROUND

In kidney transplantation, concerns have been raised regarding increased incidence of viral opportunistic infections in hepatitis C virus (HCV) nucleic acid test (NAT)-negative (-) recipients who received HCV NAT-positive (+) donor kidneys, specifically BK polyomavirus (BKPyV), cytomegalovirus (CMV), and Epstein-Barr virus (EBV). The purpose of this study was to determine the incidence of these three viral opportunistic infections in HCV NAT- recipients who have undergone kidney transplantation with HCV NAT+ donor kidneys at our institution.

METHODS

This was an Institutional Review Board-approved, single-center, retrospective case-control study of HCV NAT- kidney transplant recipients with HCV NAT+ donors from 2018 to 2021. The primary outcome was the cumulative incidence of viral infections of BKPyV, CMV, and/or EBV within 1 year following kidney transplantation.

RESULTS

A total of 231 patients were included, 77 in the exposed (donor HCV NAT+) group and 154 in the control (donor HCV NAT-) group. The adjusted cumulative incidence of viremia within 1 year did not statistically differ between groups (77% exposed group versus 66% for the control group, hazard ratio 1.34, 95% confidence interval 0.95-1.89). In addition, no statistically significant differences were observed for secondary outcomes with the exception of CMV viremia (62% exposed versus 49% control, p = 0.021). However, there were more patients in the exposed group at high risk for CMV viremia based on serostatus (CMV Donor+/Recipient-, D+/R-).

CONCLUSION

Among patients who received HCV NAT+ donor kidneys, no clear association was observed between exposure to HCV NAT+ donor kidneys and viral infections of BKPyV, CMV, or EBV.

Sulfonamide Prodrugs with a Two-Stage Release Mechanism for the Efficient Delivery of the TLR4 Antagonist TAK-242

We previously demonstrated that the potent TLR4 inhibitor TAK-242 could be covalently conjugated to pancreatic islets using a linker that afforded an effective sustained delivery of the active drug after transplant. This drug-eluting tissue achieved local inhibition of TLR4-linked inflammation and proved beneficial to the islet graft survival. Here, we describe a new family of prodrugs with a modular design featuring a self-immolative para-aminobenzyl spacer bonded directly to the TAK-242 sulfonamide nitrogen, a tether for bioconjugation, and a β-eliminative arylsulfone "trigger". The inclusion of the para-aminobenzyl spacer affords a more stable prodrug which exhibits complex drug-release kinetics due to a two-stage release mechanism. This manuscript reports the preparation and characterization of several TAK-242 prodrugs fitted with different triggers and linkers and demonstrates that these second-generation prodrugs effectively release TAK-242 while avoiding nonproductive sulfonamide hydrolysis.

LPS-Induced Liver Injury of Magang Geese through Toll-like Receptor and MAPK Signaling Pathway

Lipopolysaccharide (LPS) is one of the main virulence factors of Gram-negative bacteria. In the process of waterfowl breeding, an inflammatory reaction due to LPS infection is easily produced, which leads to a decline in waterfowl performance. The liver plays a vital role in the immune response and the removal of toxic components. Therefore, it is necessary to study the mechanism of liver injury induced by LPS in goose. In this study, a total of 100 1-day-old goslings were randomly divided into a control group and LPS group after 3 days of pre-feeding. On days 21, 23, and 25 of the formal experiment, the control group was intraperitoneally injected with 0.5 mL normal saline, and the LPS group was intraperitoneally injected with LPS 2 mg/(kg body weight) once a day. On day 25 of the experiment, liver samples were collected 3 h after the injection of saline and LPS. The results of histopathology and biochemical indexes showed that the livers of the LPS group had liver morphological structure destruction and inflammatory cell infiltration, and the levels of ALT and AST were increased. Next, RNA sequencing analysis was used to determine the abundances and characteristics of the transcripts, as well as the associated somatic mutations and alternative splicing. We screened 727 differentially expressed genes (DEGs) with p < 0.05 and |log2(Fold Change)| ≥ 1, as the thresholds; GO and KEGG enrichment analysis showed that LPS-induced liver injury may be involved in the Toll-like receptor signaling pathway, MAPK signaling pathway, NOD-like receptor signaling pathway, FoxO, and PPAR signaling pathway. Finally, we intersected the genes enriched in the key pathway of LPS-induced liver injury with the top 50 key genes in protein−protein interaction networks to obtain 28 more critical genes. Among them, 17 genes were enriched in Toll-like signaling pathway and MAPK signaling pathway. Therefore, these results suggest that LPS-induced liver injury in geese may be the result of the joint action of Toll-like receptor, MAPK, NOD-like receptor, FoxO, and PPAR signaling pathway. Among them, the TLR7-mediated MAPK signaling pathway plays a major role.

Pluripotent Stem Cell-Derived Hepatocytes Inhibit T Cell Proliferation In Vitro through Tryptophan Starvation

Regenerative medicine aims to replace damaged tissues by stimulating endogenous tissue repair or by transplanting autologous or allogeneic cells. Due to their capacity to produce unlimited numbers of cells of a given cell type, pluripotent stem cells, whether of embryonic origin or induced via the reprogramming of somatic cells, are of considerable therapeutic interest in the regenerative medicine field. However, regardless of the cell type, host immune responses present a barrier to success. The aim of this study was to investigate in vitro the immunological properties of human pluripotent stem cell (PSC)-derived hepatocyte-like cells (HLCs). These cells expressed MHC class I molecules while they lacked MHC class II and co-stimulatory molecules, such as CD80 and CD86. Following stimulation with IFN-γ, HLCs upregulated CD40, PD-L1 and MHC class I molecules. When co-cultured with allogeneic T cells, HLCs did not induce T cell proliferation; furthermore, when T cells were stimulated via αCD3/CD28 beads, HLCs inhibited their proliferation via IDO1 and tryptophan deprivation. These results demonstrate that PSC-derived HLCs possess immunoregulatory functions, at least in vitro.

Cyclosporine A, in Contrast to Rapamycin, Affects the Ability of Dendritic Cells to Induce Immune Tolerance Mechanisms

Following organ transplantation, it is essential that immune tolerance is induced in the graft recipient to reduce the risk of rejection and avoid complications associated with the long-term use of immunosuppressive drugs. Immature dendritic cells (DCs) are considered to promote transplant tolerance and may minimize the risk of graft rejection. The aim of the study was to evaluate the effects of immunosuppressive agents: rapamycin (Rapa) and cyclosporine A (CsA) on generation of human tolerogenic DCs (tolDCs) and also to evaluate the ability of these cells to induce mechanisms of immune tolerance. tolDCs were generated in the environment of Rapa or CsA. Next, we evaluated the effects of these agents on surface phenotypes (CD11c, MHC II, CD40, CD80, CD83, CD86, CCR7, TLR2, TLR4), cytokine production (IL-4, IL-6, IL-10, IL-12p70, TGF-β), phagocytic capacity and resistant to lipopolysaccharide activation of these DCs. Moreover, we assessed ability of such tolDCs to induce T cell activation and apoptosis, Treg differentiation and production of Th1- and Th2-characteristic cytokine profile. Data obtained in this study demonstrate that rapamycin is effective at generating maturation-resistant tolDCs, however, does not change the ability of these cells to induce mechanisms of immune tolerance. In contrast, CsA affects the ability of these cells to induce mechanisms of immune tolerance, but is not efficient at generating maturation-resistant tolDCs.

TLR2 and TLR4 mRNA expression levels in liver transplant patients with acute rejection

Toll-like receptors (TLRs) have important role in transplant outcomes by activating the innate immune system and production of pro-inflammatory cytokines, leading to graft rejection. We assessed the expression level of TL2 and TLR4 in acute rejection (AR) on the 1st and 7th^-day post-transplantation. TLR2 and TLR4 expressions were evaluated by real-time PCR in both the AR group (n = 50) and non-AR (n = 50), compared with the control group. Also, the correlation of the expression levels of TLRs between both the 1st and 7th day was analyzed. ROC curve analysis was used to determine the cut-off value for TLRs expression. TLR4 mRNA expression was significantly up-regulated in AR patients vs. the controls on the 1st day (p ≤ 0.05) and it was down-regulated in non-AR vs. controls on the 1st day (p ≤ 0.05). Also, TLR4 expression had decreased in both AR and non-AR groups vs. control on the 7th day (p ≤ 0.05). Both TLR2 and TLR4 expression in comparison to non-AR had increased in the AR group on the 7th day (p ≤ 0.05). TLR2 expression positively correlated between 1st and 7th day in AR (r = 0.3, (p ≤ 0.05) and non-AR group (r = 0.2, p ≤ 0.05). ROC curve analysis showed a cut-off value of TLR2 up to 0.98 with sensitivity 71.05 (95%CI = 54.1-84.6) and specificity 63.27 (95%CI = 48.3-76.6) that could distinguish between AR and non-AR group (p ≤ 0.05). The data support that both TLR2 and TLR4 expression have an effective role in AR after liver transplantation and could be used as possible biomarkers for AR to choose better therapeutic strategies based on immunological aspects.

Role of Innate Immunity in Pediatric Post-transplant Idiopathic Liver Fibrosis

Pediatric post-transplant idiopathic liver fibrosis is an unexplained graft fibrosis that occurs in symptom-free children without acute rejection and surgical complications. Despite a lack of consensus on the subject, the development of pediatric post-transplant idiopathic liver fibrosis is believed to be the result of multiple potential factors, including ischemia-reperfusion injury, allogeneic acute and chronic rejection, viral hepatitis recurrence, opportunistic infection, and drug-induced liver damage. Among them, there is growing evidence that innate immunity may also have a unique role in this progression. This study reviews the features of pediatric post-transplant idiopathic liver fibrosis and discusses current studies illustrating the potential mechanisms of liver allograft tolerance induced by intrahepatic innate immunity, the role of components including Toll-like receptors (TLRs), interferons (IFN), dendritic cells (DC), natural killer cells (NK cells), NKT cells, neutrophils, and Kupffer cells, as well as their possibly relevant role in the development of pediatric post-transplant idiopathic liver fibrosis.

The impact of liver transplant recipient and donor genetic variability on tacrolimus exposure and transplant outcome

This study investigated the effect of recipient and donor genetic variability on dose-adjusted steady-state tacrolimus concentrations (C_ss ) and clinical outcomes 3 and 6 months after liver transplant. Twenty-nine recipients and matched donor blood samples were genotyped for 27 single nucleotide polymorphisms including CYP3A5*3 (rs776746), ABCB1 haplotype and immune genes. Associations between genetic variability and clinical parameters and C_ss and the occurrence of rejection and nephrotoxicity were analysed by multivariate and multinomial logistic regression modelling and Jonckheere-Terpstra tests examined the impact of combined donor/recipient CYP3A5 expression on C_ss . At 3 months post-transplant modelling revealed an association between tacrolimus C_ss and recipient CASP1 rs580523 genotype (P = 0.005), accounting for 52% C_ss variance. Jonckheere-Terpstra tests revealed that as combined donor/recipient CYP3A5 expression increased, C_ss decreased (P = 0.010 [3 months], 0.018 [6 months]). As this is the first report of CASP1 genetic variability influencing tacrolimus C_ss , further validation in larger cohorts is required.

The regulation of interferon type I pathway-related genes RSAD2 and ETV7 specifically indicates antibody-mediated rejection after kidney transplantation

CONTEXT

Antibody-mediated rejection (ABMR) after kidney transplantation (KTx) remains the crucial obstacle to successful long-term graft function. The identification of gene signatures involved in ABMR could grant the basis for better prevention and treatment strategies.

OBJECTIVE

The identification of gene signatures in whole blood cells specific for ABMR after KTx.

MATERIALS AND METHODS

Total RNA from blood cells of 16 kidney-transplanted patients with ABMR, stable graft function (SGF), and with T-cell-mediated rejection (TCMR) was isolated. Gene expression was determined by high-throughput sequencing followed by validation and analyses of differentially expressed candidates on mRNA level and on protein level in a large patient cohort (n = 185) in patients with SGF, urinary tract infection (UTI), borderline rejection (BL), TCMR, ABMR, and interstitial fibrosis and tubular atrophy.

RESULTS

From the 570 genes detected, 111 discriminated ABMR from SGF and TCMR. A distinct enrichment of interferon (IFN) type I and type II signature gene set was observed. The expression of candidate genes IFIT1, ETV7, and RSAD2 distinguished ABMR patients from patients with SGF and also TCMR, whereas ETV7 and RSAD2 differentiated ABMR also from BL.

CONCLUSION

The IFN-inducible genes ETV7 and RSAD2 represent specific biomarkers for ABMR episodes after KTx.

Liver X Receptors Activation Attenuates Ischemia Reperfusion Injury of Liver Graft in Rats

Purpose: Suppression of the Toll like receptor 4 (TLR4)-nuclear factor-κB (NF-κB) signaling was critical in protection against liver IRI. Previous studies revealed that Liver X receptors (LXRs) activation could antagonize TLR4-NF-κB signaling. The purpose of this study is to determine whether LXRs agonist GW3965 can suppress the TLR4-NF-κB signaling during liver transplantation and protect ischemia-reperfusion injury (IRI). Materials and Methods: Sprague Dawley (SD) rats were used to perform orthotropic liver transplantation. Donors were pretreatment with GW3965 (0.3 mg/kg) through caudal vein injection 30 min before the surgery. The followings were analyzed after transplantation: alanine aminotransferase (ALT), interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) level in serum, ATP binding cassette transporter A1 (Abca1) expression, NF-κB transcriptional activity, apoptosis and histological injury. Results: GW3965 pretreatment significantly ameliorated the degree of IRI associated with the effects of upregulating Abca1 expression, inhibiting NF-κB transcriptional activity, and downregulating TNF-α and IL-6 level. Conclusion: LXRs activation attenuated hepatic IRI by preventing TLR4-NF-κB signaling.

A novel immune function biomarker identifies patients at risk of clinical events early following liver transplantation

Balancing immunosuppression after liver transplant is difficult, with clinical events common. We investigate whether a novel immune biomarker based on a laboratory platform with widespread availability that measures interferon γ (IFNγ) after stimulation with a lyophilized ball containing an adaptive and innate immune stimulant can predict events following transplantation. A total of 75 adult transplant recipients were prospectively monitored in a blinded, observational study; 55/75 (73.3%) patients experienced a total of 89 clinical events. Most events occurred within the first month. Low week 1 results were significantly associated with risk of early infection (area under the receiver operating characteristic curve [AUROC], 0.74; P = 0.008). IFNγ ≤ 1.30 IU/mL (likelihood ratio positive, 1.93; sensitivity, 71.4%; specificity, 63.0%) was associated with the highest risk for infection with minimal rejection risk. Nearly half the cohort (27/60, 45.0%) expressed IFNγ ≤ 1.30 IU/mL. Moreover, an elevated week 1 result was significantly associated with the risk of rejection within the first month after transplant (AUROC, 0.77; P = 0.002), but no episodes of infection. On multivariate logistic regression, IFNγ ≥ 4.49 IU/mL (odds ratio, 4.75) may be an independent predictor of rejection (P = 0.05). In conclusion, low IFNγ suggesting oversuppression is associated with infections, whereas high IFNγ indicating undersuppression is associated with rejection. This assay offers the potential to allow individualization and optimization of immunosuppression that could fundamentally alter the way patients are managed following transplantation. Liver Transplantation 23 487-497 2017 AASLD.

Nobiletin ameliorates ischemia-reperfusion injury by suppressing the function of Kupffer cells after liver transplantation in rats

This study aims to explore the protective effects of nobiletin against hepatic ischemia-reperfusion (IR) injury after liver transplantation. Kupffer cells (KCs) were activated and co-cultured with different concentration of nobiletin for 24h in vitro, inflammatory products and activity of TLR4/NF-κB signaling pathway were detected. Sprague-Dawley rats were selected and underwent orthotopic liver transplantation. Donors were injected intravenously with nobiletin (50mg/kg) or saline solution, once a day for 1 week before the surgery. Recipients were randomly paired and sacrificed at the indicated time points (3, 6, and 24h after the surgery), the graft liver tissues and blood samples were collected for analysis. Hepatic function, inflammatory mediators, apoptosis of hepatocytes, histological changes, KCs and CD4+ T-lymphocyte infiltration were assessed. Results showed nobiletin dose-dependently suppressed the expression of inflammatory mediators and the activity of TLR4/NF-κB signaling pathway in activated KCs. Furthermore, nobiletin alleviated liver damage induced by IR in vivo, significantly decreased the serum levels of alanine aminotransferase, aspartate transaminase, inflammatory cytokines and alleviated the histopathology changes. Moreover, liver in the nobiletin treated group exhibited less KCs and CD4+ lymphocyte infiltration and lower hepatocyte apoptosis after operation. In addition, activity of TLR4/NF-κB signaling pathway in KCs was also suppressed, consistent with the results in vitro. Collectively, Nobiletin can ameliorate IR injury after liver transplantation and may be a promising new strategy to protect against liver IR injury.

The CD8 T-cell response during tolerance induction in liver transplantation

Both experimental and clinical studies have shown that the liver possesses unique tolerogenic properties. Liver allografts can be spontaneously accepted across complete major histocompatibility mismatch in some animal models. In addition, some liver transplant patients can be successfully withdrawn from immunosuppressive medications, developing ‘operational tolerance'. Multiple mechanisms have been shown to be involved in inducing and maintaining alloimmune tolerance associated with liver transplantation. Here, we focus on CD8 T-cell tolerance in this setting. We first discuss how alloreactive cytotoxic T-cell responses are generated against allografts, before reviewing how the liver parenchyma, donor passenger leucocytes and the host immune system function together to attenuate alloreactive CD8 T-cell responses to promote the long-term survival of liver transplants.

Functional Immune Anatomy of the Liver-As an Allograft

The liver is an immunoregulatory organ in which a tolerogenic microenvironment mitigates the relative "strength" of local immune responses. Paradoxically, necro-inflammatory diseases create the need for most liver transplants. Treatment of hepatitis B virus, hepatitis C virus, and acute T cell-mediated rejection have redirected focus on long-term allograft structural integrity. Understanding of insults should enable decades of morbidity-free survival after liver replacement because of these tolerogenic properties. Studies of long-term survivors show low-grade chronic inflammatory, fibrotic, and microvascular lesions, likely related to some combination of environment insults (i.e. abnormal physiology), donor-specific antibodies, and T cell-mediated immunity. The resultant conundrum is familiar in transplantation: adequate immunosuppression produces chronic toxicities, while lightened immunosuppression leads to sensitization, immunological injury, and structural deterioration. The "balance" is more favorable for liver than other solid organ allografts. This occurs because of unique hepatic immune physiology and provides unintended benefits for allografts by modulating various afferent and efferent limbs of allogenic immune responses. This review is intended to provide a better understanding of liver immune microanatomy and physiology and thereby (a) the potential structural consequences of low-level, including allo-antibody-mediated injury; and (b) how liver allografts modulate immune reactions. Special attention is given to the microvasculature and hepatic mononuclear phagocytic system.

The Role of Toll-Like Receptor 4 in Infectious and Noninfectious Inflammation

Toll-like receptor 4 (TLR4) belongs to the family of pattern recognition receptors (PRRs). They are highly conserved receptors that recognize conserved pathogen-associated molecular patterns (PAMPs), thus representing the first line of defense against infections. TLR4 has been long recognized as the sensing receptor for gram-negative lipopolysaccharide (LPS). In addition, it also binds endogenous molecules produced as a result of tissue injury. Hence, TLR4 represents a key receptor on which both infectious and noninfectious stimuli converge to induce a proinflammatory response. TLR4-mediated inflammation, triggered by exogenous or endogenous ligands, is also involved in several acute and chronic diseases, having a pivotal role as amplifier of the inflammatory response. This review focuses on the research progress about the role of TLR4 activation in infectious and noninfectious (e.g., sterile) inflammation and the effects of TLR4 signaling in some pathological conditions.

Blocking cold-inducible RNA-binding protein protects liver from ischemia-reperfusion injury

Cold-inducible RNA-binding protein (CIRP) is a nuclear protein that has been recently identified as a novel inflammatory mediator in hemorrhagic shock and sepsis. We hypothesized that CIRP acts as a potent inflammatory mediator in hepatic ischemia-reperfusion (I/R), and thus blocking CIRP protects against I/R-induced liver injury. Male C57BL/6 mice were subjected to 70% hepatic ischemia by microvascular clamping of the hilum of the left and median liver lobes for 60 min, followed by reperfusion. Anti-CIRP antibody (1 mg/kg body weight) or vehicle (normal saline) in 0.2 mL was injected via the internal jugular vein at the beginning of the reperfusion. Blood and liver tissues were collected 24 h after I/R for various measurements, and a 10-day survival study was performed. Cold-inducible RNA-binding protein released into the circulation was significantly increased 24 h after hepatic I/R. Anti-CIRP antibody treatment markedly reduced hepatocellular damage markers and significantly improved the liver microarchitecture. Anti-CIRP also reduced the systemic and local inflammation demonstrated by attenuation in both serum and hepatic levels of interleukin 6. The expression of neutrophil-attracting chemokine as well as liver neutrophil infiltration was reduced by anti-CIRP treatment. Anti-CIRP also dramatically decreased the amount of apoptosis and nitrosative stress, evidenced by decrease in TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) staining and inducible nitric oxide synthase and cyclooxygenase 2 levels, respectively. Finally, the 10-day survival rate was increased from 37.5% in the vehicle group to 75% in the anti-CIRP treatment group. Thus, targeting CIRP offers potential therapeutic implications in the treatment of hepatic I/R injury.

Kupffer cells and liver transplantation

Nowadays, liver transplantation is globally considered the most effective treatment for end-stage liver diseases. Ischemia-reperfusion (I/R) injury and immune rejection response (IRR) are the two major imperfections which severely affect the recipients' prognosis and survival rate without satisfactory clinical management strategies. Therefore, exploring effective methods to improve I/R injury and IRR have important clinical significance under circumstances of shortage of donor livers. Kupffer cells (KCs) are the largest population of antigen representing cells (APCs) which settle in the liver. As the first defensive line of the live, KCs exhibit various biological effects. However, the exact mechanisms responsible for the role of KCs in I/R injury and IRR remain elusive. We hereby review the current finding about the role of KCs in I/R injury and IRR.

Role of toll-like receptors in immune activation and tolerance in the liver

Liver has a unique vascular system receiving the majority of the blood supply from the gastrointestinal tract through the portal vein and faces continuous exposure to foreign pathogens and commensal bacterial products. These gut-derived antigens stimulate liver cells and result in a distinctive immune response via a family of pattern recognition receptors, the Toll-like receptors (TLRs). TLRs are expressed on Kupffer cells, dendritic cells, hepatic stellate cells, endothelial cells, and hepatocytes in the liver. The crosstalk between gut-derived antigens and TLRs on immune cells trigger a distinctive set of mechanisms to induce immunity, contributing to various acute and chronic liver diseases including liver cirrhosis and hepatocellular carcinoma. Accumulating evidence has shown that TLRs stimulation by foreign antigens induces the production of immunoactivating and immunoregulatory cytokines. Furthermore, the immunoregulatory arm of TLR stimulation can also control excessive tissue damage. With this knowledge at hand, it is important to clarify the dual role of disease-specific TLRs as activators and regulators, especially in the liver. We will review the current understanding of TLR signaling and subsequent immune activation and tolerance by the innate immune system in the liver.