Increased Th17 rather than Th1 alloimmune response is associated with cardiac allograft vasculopathy after hypothermic preservation in the rat

Melatonin Synergizes With Mesenchymal Stromal Cells Attenuates Chronic Allograft Vasculopathy

Background

Chronic rejection characterized by chronic allograft vasculopathy (CAV) remains a major obstacle to long-term graft survival. Due to multiple complicated mechanisms involved, a novel therapy for CAV remains exploration. Although mesenchymal stromal cells (MSCs) have been ubiquitously applied to various refractory immune-related diseases, rare research makes a thorough inquiry in CAV. Meanwhile, melatonin (MT), a wide spectrum of immunomodulator, plays a non-negligible role in transplantation immunity. Here, we have investigated the synergistic effects of MT in combination with MSCs in attenuation of CAV.

Methods

C57BL/6 (B6) mouse recipients receiving BALB/c mouse donor aorta transplantation have been treated with MT and/or adipose-derived MSCs. Graft pathological changes, intragraft immunocyte infiltration, splenic immune cell populations, circulating donor-specific antibodies levels, cytokine profiles were detected on post-operative day 40. The proliferation capacity of CD4+ and CD8+ T cells, populations of Th1, Th17, and Tregs were also assessed in vitro.

Results

Grafts in untreated recipients developed a typical pathological feature of CAV characterized by intimal thickening 40 days after transplantation. Compared to untreated and monotherapy groups, MT in combination with MSCs effectively ameliorated pathological changes of aorta grafts indicated by markedly decreased levels of intimal hyperplasia and the infiltration of CD4+ cells, CD8+ cells, and macrophages, but elevated infiltration of Foxp3+ cells. MT either alone or in combination with MSCs effectively inhibited the proliferation of T cells, decreased populations of Th1 and Th17 cells, but increased the proportion of Tregs in vitro. MT synergized with MSCs displayed much fewer splenic populations of CD4+ and CD8+ T cells, Th1 cells, Th17 cells, CD4+ central memory T cells (Tcm), as well as effector memory T cells (Tem) in aorta transplant recipients. In addition, the percentage of splenic Tregs was substantially increased in the combination therapy group. Furthermore, MT combined with MSCs markedly reduced serum levels of circulating allospecific IgG and IgM, as well as decreased the levels of pro-inflammatory IFN-γ, TNF-α, IL-1β, IL-6, IL-17A, and MCP-1, but increased the level of IL-10 in the recipients.

Conclusions

These data suggest that MT has synergy with MSCs to markedly attenuate CAV and provide a novel therapeutic strategy to improve the long-term allograft acceptance in transplant recipients.

The Fetal-Maternal Immune Interface in Uterus Transplantation

Uterus transplants (UTxs) have been performed worldwide. Overall frequencies have been low, but globally initiated UTx programs are expected to increase clinical implementation. The uterus constitutes a unique immunological environment with specific features of tissue renewal and a receptive endometrium. Decidual immune cells facilitate embryo implantation and placenta development. Although UTx adds to the complexity of immunity during pregnancy and transplantation, the procedure provides a unique clinical and experimental model. We posit that understanding the distinct immunological properties at the interface of the transplanted uterus, the fetus and maternal circulation might provide valuable novel insights while improving outcomes for UTx. Here, we discuss immunological challenges and opportunities of UTx affecting mother, pregnancy and healthy livebirths.

Damage-Associated Molecular Patterns in Myocardial Infarction and Heart Transplantation: The Road to Translational Success

In the setting of myocardial infarction (MI), ischemia reperfusion injury (IRI) occurs due to occlusion (ischemia) and subsequent re-establishment of blood flow (reperfusion) of a coronary artery. A similar phenomenon is observed in heart transplantation (HTx) when, after cold storage, the donor heart is connected to the recipient's circulation. Although reperfusion is essential for the survival of cardiomyocytes, it paradoxically leads to additional myocardial damage in experimental MI and HTx models. Damage (or danger)-associated molecular patterns (DAMPs) are endogenous molecules released after cellular damage or stress such as myocardial IRI. DAMPs activate pattern recognition receptors (PRRs), and set in motion a complex signaling cascade resulting in the release of cytokines and a profound inflammatory reaction. This inflammatory response is thought to function as a double-edged sword. Although it enables removal of cell debris and promotes wound healing, DAMP mediated signalling can also exacerbate the inflammatory state in a disproportional matter, thereby leading to additional tissue damage. Upon MI, this leads to expansion of the infarcted area and deterioration of cardiac function in preclinical models. Eventually this culminates in adverse myocardial remodeling; a process that leads to increased myocardial fibrosis, gradual further loss of cardiomyocytes, left ventricular dilation and heart failure. Upon HTx, DAMPs aggravate ischemic damage, which results in more pronounced reperfusion injury that impacts cardiac function and increases the occurrence of primary graft dysfunction and graft rejection via cytokine release, cardiac edema, enhanced myocardial/endothelial damage and allograft fibrosis. Therapies targeting DAMPs or PRRs have predominantly been investigated in experimental models and are potentially cardioprotective. To date, however, none of these interventions have reached the clinical arena. In this review we summarize the current evidence of involvement of DAMPs and PRRs in the inflammatory response after MI and HTx. Furthermore, we will discuss various current therapeutic approaches targeting this complex interplay and provide possible reasons why clinical translation still fails.

A review of myocardial ischaemia/reperfusion injury: Pathophysiology, experimental models, biomarkers, genetics and pharmacological treatment

Cardiovascular diseases are known to be the most fatal diseases worldwide. Ischaemia/reperfusion (I/R) injury is at the centre of the pathology of the most common cardiovascular diseases. According to the World Health Organization estimates, ischaemic heart disease is the leading global cause of death, causing more than 9 million deaths in 2016. After cardiovascular events, thrombolysis, percutaneous transluminal coronary angioplasty or coronary bypass surgery are applied as treatment. However, after restoring coronary blood flow, myocardial I/R injury may occur. It is known that this damage occurs due to many pathophysiological mechanisms, especially increasing reactive oxygen types. Besides causing cardiomyocyte death through multiple mechanisms, it may be an important reason for affecting other cell types such as platelets, fibroblasts, endothelial and smooth muscle cells and immune cells. Also, polymorphonuclear leukocytes are associated with myocardial I/R damage during reperfusion. This damage may be insufficient in patients with co-morbidity, as it is demonstrated that it can be prevented by various endogenous antioxidant systems. In this context, the resulting data suggest that optimal cardioprotection may require a combination of additional or synergistic multi-target treatments. In this review, we discussed the pathophysiology, experimental models, biomarkers, treatment and its relationship with genetics in myocardial I/R injury. SIGNIFICANCE OF THE STUDY: This review summarized current information on myocardial ischaemia/reperfusion injury (pathophysiology, experimental models, biomarkers, genetics and pharmacological therapy) for researchers and reveals guiding data for researchers, especially in the field of cardiovascular system and pharmacology.

Cell Therapy in Solid Organ Transplantation

Transplantation is the only cure for end-stage organ failure. Current immunosuppressive drugs have two major limitations: 1) non antigen specificity, which increases the risk of cancer and infection diseases, and 2) chronic toxicity. Cell therapy appears to be an innovative and promising strategy to minimize the use of immunosuppression in transplantation and to improve long-term graft survival. Preclinical studies have shown efficacy and safety of using various suppressor cells, such as regulatory T cells, regulatory B cells and tolerogenic dendritic cells. Recent clinical trials using cellbased therapies in solid organ transplantation also hold out the promise of improving efficacy. In this review, we will briefly go over the rejection process, current immunosuppressive drugs, and the potential therapeutic use of regulatory cells in transplantation.

Rapamycin Modulate Treg/Th17 Balance via Regulating Metabolic Pathways: A Study in Mice

A regulatory T (Treg) cell/T helper 17 (Th17) cell imbalance is involved in many autoimmune diseases. Rapamycin (Rapa), a clinically used immunosuppressive drug, has been shown to inhibit Th17 cell differentiation but promote Treg cell generation. In this study, we aimed to study the mechanism of Rapa acting on Treg and Th17 cell differentiation. Purified mouse CD4⁺CD25^- T cells were stimulated and polarized in vitro to generate Th17 or Treg cells in the presence or absence of Rapa. We first confirmed that Rapa inhibited the differentiation of Th17 cells and greatly promoted Treg cell generation in vitro. As metabolic pathways play a key role in T cell differentiation, we then detected the metabolic programs in Rapa-treated T cells. We found that Rapa blocked glycolysis in induced Th17 cells, evidenced by reduced glucose uptake, and inhibited expression of glucose transporter 1 and the rate-limiting enzyme HK2. In addition, the expression of c-Myc and of HIF-1α transcription factor, which regulate many genes involved in glycolysis, were inhibited by Rapa. Conversely, Rapa promoted fatty acid oxidation (FAO) metabolism in differentiated Treg cells, with the elevation of FAO product β-hydroxybutyrate, and increased expression of ATGL and CPT1A, the key enzymes of FAO in differentiated Treg cells. The expression of phospho-AMPKα, the key signal in the regulation of FAO, was also promoted in Rapa-treated induced Treg cells. Together, these findings indicated that Rapa abrogated glycolysis in Th17 cells but facilitated FAO in induced Treg cells, which may underlie the mechanism by which Rapa regulates the Treg/Th17 balance.

Th1, Th2, Th17 cell subsets in two different immunosuppressive protocols in renal allograft recipients (Sirolimus vs mycophenolate mofetil): A cohort study

Long-term use of calcineurin inhibitors (CNI) is associated with nephrotoxicity, which is an important cause of renal dysfunction. Therefore, CNI-minimization strategies which decrease the CNI nephrotoxicity under the protection of additional immunosuppressant drugs have been developed. The aim of current cohort study was to compare the effect of two immunosuppressive protocols [tacrolimus (TAC) in combination with mycophenolate mofetil (MMF) and prednisolone (PRED) versus TAC in combination with sirolimus (SRL) and prednisolone] on the frequency of T helper cell subsets (Th1, Th2 and Th17 cells) and their associated cytokine (IFN-γ, IL-4 and IL-17A) levels in renal allograft recipients. In this study, renal transplant recipients who received induction therapy (Antithymocyte globulin) and were also on triple immunosuppressive therapy were included and divided in to two groups: Group A was comprised 14 patients who received TAC, MMF and PERD whereas group B was composed of 10 patients who received TAC, SRL and PERD. The frequency of Th1, Th2 and Th17 cells in the peripheral blood mononuclear cells (PBMCs) of the patients was analyzed by flow cytometry before and 4 months after transplantation. In addition, IFN-γ, IL-4 and IL-17A concentrations in PBMC culture supernatants of patients before and 4 months after transplantation were quantified by ELISA. The results of our study showed that TAC, MMF and PRED protocol did not diminish the frequency of Th17 cells at 4 months post-transplantation (5% ± 2.5) compared with pre-transplantation (2.3% ± 1; P < 0.05). However, Th17 (3.6% ± 1.5 pre-transplantation vs 2.2% ± 0.9 at 4 months post-transplantation; P < 0.05), Th2 (1.4% ± 0.3 pre-transplantation vs 0.8% ± 0.4 at 4 months post-transplantation; P < 0.05) cell subsets and IL-4 concentration (71.5 pg/ml ± 12 pre-transplantation vs 62.5 pg/ml ±4.4 at 4 months post-transplantation; P < 0.05) were significantly decreased after transplantation in patients who had received SRL, TAC and PRED. In conclusion, the data of the current study suggest that using reduced dose of TAC in SRL, TAC and PRED protocol is in favor of allograft survival; however a cohort study with larger sample size is needed for confirming our results.

Clinical significance of Th17 cells in kidney transplantation

Transplantation research has focused on cytotoxic T-cell and plasma cell/B-cell-targeted strategies, but little attention has been paid to the role of T helper 17 (Th17) cells in allograft dysfunction. However, accumulating evidence suggests that Th17 cells contribute to the development of acute and chronic allograft injury after transplantation of various organs, including the kidney. This review summarizes recent reports on the role of Th17 cells in kidney transplantation. Means of improving allograft outcomes by targeting the Th17 pathway are also suggested.

Danger signals in regulating the immune response to solid organ transplantation

Endogenous danger signals, or damage-associated molecular patterns (DAMPs), are generated in response to cell stress and activate innate immunity to provide a pivotal mechanism by which an organism can respond to damaged self. Accumulating experimental and clinical data have established the importance of DAMPs, which signal through innate pattern recognition receptors (PRRs) or DAMP-specific receptors, in regulating the alloresponse to solid organ transplantation (SOT). Moreover, DAMPs may incite distinct downstream cellular responses that could specifically contribute to the development of allograft fibrosis and chronic graft dysfunction. A growing understanding of the role of DAMPs in directing the immune response to transplantation has suggested novel avenues for the treatment or prevention of allograft rejection that complement contemporary immunosuppression and could lead to improved outcomes for solid organ recipients.

Effect of Cold Preservation on Chronic Rejection in a Rat Hindlimb Transplantation Model

BACKGROUND

Previous studies on solid organ transplantation have shown that cold ischemia contributes to the development of chronic allograft vasculopathy. The authors evaluated the effect of cold ischemia on the development of chronic rejection in vascularized composite allotransplantation.

METHODS

Thirty rat hindlimbs were transplanted and divided into two experimental groups: immediate transplantation and transplantation after 7 hours of cold ischemia. The animals received daily low-dose immunosuppression with cyclosporine A for 2 months. Intimal proliferation, arterial permeability rate, leukocyte infiltration, and tissue fibrosis were assessed. The CD3, CD4, CD8, CD20, and CD68 cells per microscopic field (200×) were counted, and C4d deposition was investigated. Cytokine RNA analysis was performed to measure tumor necrosis factor-α, interleukin-6, and interleukin-10 levels.

RESULTS

Significant differences were found in the intimal proliferation and arterial permeability rate between the two groups (p = 0.004). The arterial permeability rate worsened in the most distal and small vessels (p = 0.047). The numbers of CD3, CD8, CD20, and CD68 were also statistically higher in the cold ischemia group (p < 0.05, all levels). A trend toward significance was observed with C4d deposition (p = 0.059). No differences were found in the RNA of cytokines.

CONCLUSIONS

An association between cold ischemia and chronic rejection was observed in experimental vascularized composite allotransplantation. Chronic rejection intensity and distal progression were significantly related with cold ischemia. The leukocyte infiltrates in vascularized composite allotransplantation components were a rejection marker; however, their exact implication in monitoring and their relation with cold ischemia are yet to be clarified.

Ischemia/Reperfusion

Ischemic disorders, such as myocardial infarction, stroke, and peripheral vascular disease, are the most common causes of debilitating disease and death in westernized cultures. The extent of tissue injury relates directly to the extent of blood flow reduction and to the length of the ischemic period, which influence the levels to which cellular ATP and intracellular pH are reduced. By impairing ATPase-dependent ion transport, ischemia causes intracellular and mitochondrial calcium levels to increase (calcium overload). Cell volume regulatory mechanisms are also disrupted by the lack of ATP, which can induce lysis of organelle and plasma membranes. Reperfusion, although required to salvage oxygen-starved tissues, produces paradoxical tissue responses that fuel the production of reactive oxygen species (oxygen paradox), sequestration of proinflammatory immunocytes in ischemic tissues, endoplasmic reticulum stress, and development of postischemic capillary no-reflow, which amplify tissue injury. These pathologic events culminate in opening of mitochondrial permeability transition pores as a common end-effector of ischemia/reperfusion (I/R)-induced cell lysis and death. Emerging concepts include the influence of the intestinal microbiome, fetal programming, epigenetic changes, and microparticles in the pathogenesis of I/R. The overall goal of this review is to describe these and other mechanisms that contribute to I/R injury. Because so many different deleterious events participate in I/R, it is clear that therapeutic approaches will be effective only when multiple pathologic processes are targeted. In addition, the translational significance of I/R research will be enhanced by much wider use of animal models that incorporate the complicating effects of risk factors for cardiovascular disease. © 2017 American Physiological Society. Compr Physiol 7:113-170, 2017.

Platelet-derived Growth Factor-B Protects Rat Cardiac Allografts From Ischemia-reperfusion Injury

BACKGROUND

Microvascular dysfunction and cardiomyocyte injury are hallmarks of ischemia-reperfusion injury (IRI) after heart transplantation. Platelet-derived growth factors (PDGF) have an ambiguous role in this deleterious cascade. On one hand, PDGF may exert vascular stabilizing and antiapoptotic actions through endothelial-pericyte and endothelial-cardiomyocyte crosstalk in the heart; and on the other hand, PDGF signaling mediates neointimal formation and exacerbates chronic rejection in cardiac allografts. The balance between these potentially harmful and beneficial actions determines the final outcome of cardiac allografts.

METHODS AND RESULTS

We transplanted cardiac allografts from Dark Agouti rat and Balb mouse donors to fully major histocompatibility complex-mismatched Wistar Furth rat or C57 mouse recipients with a clinically relevant 2-hour cold ischemia and 1-hour warm ischemia. Ex vivo intracoronary delivery of adenovirus-mediated gene transfer of recombinant human PDGF-BB upregulated messenger RNA expression of anti-mesenchymal transition and survival factors BMP-7 and Bcl-2 and preserved capillary density in rat cardiac allografts at day 10. In mouse cardiac allografts PDGF receptor-β, but not -α intragraft messenger RNA levels were reduced and capillary protein localization was lost during IRI. The PDGF receptor tyrosine kinase inhibitor imatinib mesylate and a monoclonal antibody against PDGF receptor-α enhanced myocardial damage evidenced by serum cardiac troponin T release in the rat and mouse cardiac allografts 6 hours after reperfusion, respectively. Moreover, imatinib mesylate enhanced rat cardiac allograft vasculopathy, cardiac fibrosis, and late allograft loss at day 56.

CONCLUSIONS

Our results suggest that PDGF-B signaling may play a role in endothelial and cardiomyocyte recovery from IRI after heart transplantation.

Role of TLRs and DAMPs in allograft inflammation and transplant outcomes

Graft inflammation impairs the induction of solid organ transplant tolerance and enhances acute and chronic rejection. Elucidating the mechanisms by which inflammation is induced after organ transplantation could lead to novel therapeutics to improve transplant outcomes. In this Review we describe endogenous substances--damage-associated molecular patterns (DAMPs)--that are released after allograft reperfusion and induce inflammation. We also describe innate immune signalling pathways that are activated after solid organ transplantation, with a focus on Toll-like receptors (TLRs) and their signal adaptor, MYD88. Experimental and clinical studies have yielded a large body of evidence that TLRs and MYD88 are instrumental in initiating allograft inflammation and promoting the development of acute and chronic rejection. Ongoing clinical studies are testing TLR inhibition strategies in solid organ transplantation, although avoiding compromising host defence to pathogens is a key challenge. Further elucidation of the mechanisms by which sterile inflammation is induced, maintained and amplified within the allograft has the potential to lead to novel anti-inflammatory treatments that could improve outcomes for solid organ transplant recipients.

Donor Heart Treatment With COMP-Ang1 Limits Ischemia-Reperfusion Injury and Rejection of Cardiac Allografts

The major cause of death during the first year after heart transplantation is primary graft dysfunction due to preservation and ischemia-reperfusion injury (IRI). Angiopoietin-1 is a Tie2 receptor-binding paracrine growth factor with anti-inflammatory properties and indispensable roles in vascular development and stability. We used a stable variant of angiopoietin-1 (COMP-Ang1) to test whether ex vivo intracoronary treatment with a single dose of COMP-Ang1 in donor Dark Agouti rat heart subjected to 4-h cold ischemia would prevent microvascular dysfunction and inflammatory responses in the fully allogeneic recipient Wistar Furth rat. COMP-Ang1 reduced endothelial cell-cell junction disruption of the donor heart in transmission electron microscopy during 4-h cold ischemia, improved myocardial reflow, and reduced microvascular leakage and cardiomyocyte injury of transplanted allografts during IRI. Concurrently, the treatment reduced expression of danger signals, dendritic cell maturation markers, endothelial cell adhesion molecule VCAM-1 and RhoA/Rho-associated protein kinase activation and the influx of macrophages and neutrophils. Furthermore, COMP-Ang1 treatment provided sustained anti-inflammatory effects during acute rejection and prevented the development of cardiac fibrosis and allograft vasculopathy. These results suggest donor heart treatment with COMP-Ang1 having important clinical implications in the prevention of primary and subsequent long-term injury and dysfunction in cardiac allografts.

CD11c+ Dendritic Cells Accelerate the Rejection of Older Cardiac Transplants via Interleukin-17A

BACKGROUND

Organ transplantation has seen an increased use of organs from older donors over the past decades in an attempt to meet the globally growing shortage of donor organs. However, inferior transplantation outcomes when older donor organs are used represent a growing challenge.

METHODS AND RESULTS

Here, we characterize the impact of donor age on solid-organ transplantation using a murine cardiac transplantation model. We found a compromised graft survival when older hearts were used. Shorter graft survival of older hearts was independent of organ age per se, because chimeric young or old organs repopulated with young passenger leukocytes showed comparable survival times. Transplantation of older organs triggered more potent alloimmune responses via intragraft CD11c+ dendritic cells augmenting CD4+ and CD8+ T-cell proliferation and proinflammatory cytokine production, particularly that of interleukin-17A. Of note, depletion of donor CD11c+ dendritic cells before engraftment, neutralization of interleukin-17A, or transplantation of older hearts into IL-17A(-/-) mice delayed rejection and reduced alloimmune responses to levels observed when young hearts were transplanted.

CONCLUSIONS

These results demonstrate a critical role of old donor CD11c+ dendritic cells in mounting age-dependent alloimmune responses with an augmented interleukin-17A response in recipient animals. Targeting interleukin-17A may serve as a novel therapeutic approach when older organs are transplanted.

The effect of mammalian target of rapamycin inhibition on T helper type 17 and regulatory T cell differentiation in vitro and in vivo in kidney transplant recipients

Sirolimus (SRL) is a promising alternative to calcineurin inhibitors, such as tacrolimus (TAC), in kidney transplant recipients (KTRs), but the immunological benefits of conversion from calcineurin inhibitors to SRL are not fully investigated. In the present study, we evaluated the effect of conversion from TAC to SRL on the T helper type 17/regulatory T (Th17/Treg) axis in three separate studies. First, the effect of SRL on the Th17/Treg axis was evaluated in vitro using peripheral blood mononuclear cells (PBMCs). Second, the effect of conversion from TAC to SRL on the Th17/Treg axis was studied in KTRs. Finally, the effect of SRL on CD8(+) Treg cells was evaluated. In vitro analysis of PBMCs isolated from KTRs showed that SRL suppressed Th17 cell differentiation but TAC did not. Conversion from TAC to SRL markedly decreased the number of effector memory CD8(+) T cells and significantly increased the proportion of CD4(+) and CD8(+) Treg cells compared with TAC in KTRs. SRL treatment induced the CD8(+) Treg cells, and these cells inhibited the proliferation of allogeneic CD4(+) T cells and Th17 cells. In conclusion, conversion from TAC to SRL favourably regulates Th17 and Treg cell differentiation in KTRs. These findings provide a rationale for conversion from TAC to SRL in KTRs.

Angiopoietin-2 inhibition prevents transplant ischemia-reperfusion injury and chronic rejection in rat cardiac allografts

Transplant ischemia-reperfusion injury (Tx-IRI) and allograft dysfunction remain as two of the major clinical challenges after heart transplantation. We investigated the role of angiopoietin-2 (Ang2) in Tx-IRI and rejection using fully MHC-mismatched rat cardiac allografts. We report that plasma levels of Ang2 were significantly enhanced in the human and rat recipients of cardiac allografts, but not in the rat recipients of syngrafts, during IRI. Ex vivo intracoronary treatment of rat cardiac allografts with anti-Ang2 antibody before 4-h cold preservation prevented microvascular dysfunction, endothelial cell (EC) adhesion molecule expression and leukocyte infiltration, myocardial injury and the development of cardiac fibrosis and allograft vasculopathy. Recipient preoperative and postoperative treatment with anti-Ang2 antibody produced otherwise similar effects without effecting microvascular dysfunction, and in additional experiments prolonged allograft survival. Recipient preoperative treatment alone failed to produce these effects. Moreover, ex vivo intracoronary treatment of allografts with recombinant Ang2 enhanced Tx-IRI and, in an add-back experiment, abolished the beneficial effect of the antibody. We demonstrate that neutralization of Ang2 prevents EC activation, leukocyte infiltration, Tx-IRI and the development of chronic rejection in rat cardiac allografts. Our results suggest that blocking Ang2 pathway is a novel, clinically feasible, T cell-independent strategy to protect cardiac allografts.

Inhibition of innate co-receptor TREM-1 signaling reduces CD4(+) T cell activation and prolongs cardiac allograft survival

The innate receptor "triggering-receptor-expressed-on-myeloid-cells-1" (TREM-1) enhances downstream signaling of "pattern recognition receptor" (PRR) molecules implicated in inflammatory responses. However the mechanistic role of TREM-1 in chronic heart rejection has yet to be elucidated. We examined the effect of TREM-1(+) antigen-presenting cells (APC) on alloreactive CD4(+) lymphocytes. Bm12 donor hearts were transplanted into wild-type MHC-class-II-mismatched C57BL/6J recipient mice. Progressive allograft rejection of bm12-donor hearts with decreased organ function, severe vasculopathy and allograft fibrosis was evident within 4 weeks. TREM-1(+) CD11b(+) MHC-II(+) F4/80(+) CCR2(+) APC and IFNγ-producing CD4(+) cells were detected during chronic rejection. Peptide inhibition of TREM-1 attenuated graft vasculopathy, reduced graft-infiltrating leukocytes and prolonged allograft survival, while being accompanied by sustained low levels of CD4(+) and CD8(+) cell infiltration. Remarkably, temporary inhibition of TREM-1 during early immune activation was sufficient for long-term allograft survival. Mechanistically, TREM-1 inhibition leads to reduced differentiation and proliferation of IFNγ-producing Th1 cells. In conclusion, TREM-1 influences chronic heart rejection by regulating the infiltration and differentiation of CD4(+) lymphocytes.

Establishment of a novel volume-loaded heterotopic heart transplantation model in rats

BACKGROUND

Non-volume-loaded (NL) donor hearts in the heterotopic heart transplantation model in rats undergo atrophy and thrombus formation in graft cavities after transplantation. The present study aimed to establish a novel model with volume-loaded donor hearts.

METHODS

We used Sprague-Dawley rats as donors and recipients. We established an NL model by anastomosing the donor ascending aorta and pulmonary artery end-to-side to the recipient abdominal aorta and inferior vena cava, respectively, and ligating the superior and inferior vena cava on the donor right atrium. The method of the volume-loaded (VL) model was the same as described above, except we performed an anastomosis of the donor left atrium to the recipient abdominal aorta to allow volume loading of the donor's left ventricle. We assessed the characteristics of the grafts by the surgical success rate, echocardiography, and histologic evaluation between the two models.

RESULTS

Echocardiography showed that donor left ventricle in VL models was volume loaded and had normal systolic and diastolic function compared with the NL models. The mean weight of NL hearts was significantly less than that of VL hearts. Morphologic observation revealed that thrombus formation in donor heart cavities in NL model was significantly higher than that in the VL model. The area of cardiomyocytes per high-power field in the NL model was significantly lower than that in the VL model.

CONCLUSIONS

We provide a novel VL heterotopic heart transplantation model in rats, in which hemodynamic performance of grafts is close to the normal cardiac physiologic situation; thus, the novel model will be more suitable for clinical research.

Dysregulation of Th17 cells during the early post-transplant period in patients under calcineurin inhibitor based immunosuppression

Accumulating evidence suggests that Th17 cells play a role in the development of chronic allograft injury in transplantation of various organs. However, the influence of current immunosuppressants on Th17-associated immune responses has not been fully investigated. We prospectively investigated the changes in Th17 cells in peripheral blood mononuclear cells (PBMCs) collected before and 1 and 3 months after KT in 26 patients and we investigated the suppressive effect of tacrolimus on Th17 in vitro. In the early posttransplant period, the percentage of Th17 cells and the proportion of IL-17-producing cells in the effector memory T cells (TEM) were significantly increased at 3 months after transplantation compared with before transplantation (P<0.05), whereas Th1/Th2 cells and TEM cells were significantly decreased. The degree of increase in Th17 during the early posttransplant period was significantly associated with allograft function at 1 year after transplantation (r = 0.4, P<0.05). In vitro, tacrolimus suppressed Th1 and Th2 cells in a concentration-dependent manner, but did not suppress Th17 cells even at high concentration. This suggests that current immunosuppression based on tacrolimus is inadequate to suppress Th17 cells in KTRs, and dysregulation of Th17 may be associated with the progression of CAD.

MicroRNAs and other mechanisms regulate interleukin-17 cytokines and receptors

Interleukin-17 cytokines are a family of pro-inflammatory cytokines. Our current studies found: i) IL-17 cytokines are not ubiquitously expressed, but several receptors and TRAF3IP2 are ubiquitously expressed in tissues with a few exceptions; ii) heart and vascular tissue are in the second tier of readiness to respond to IL-17 cytokine stimulation; iii) alternative transcription starting sites and alternative spliced isoforms are found in IL-17 cytokine and receptor transcripts; iv) higher hypomethylation status is associated with higher expressions of IL-17 receptors; v) the binding sites of several RNA binding proteins are found in the 3'UTRs of the mRNAs of IL-17 cytokines and receptors; and vi) numerous microRNA binding sites are statistically equivalent to that of experimentally verified microRNAs-mRNA interactions in the 3'UTRs of IL-17 cytokine and receptor mRNAs. These results suggest that mechanisms including alternative promoters, alternative splicing, RNA binding proteins, and microRNAs regulate the structures and expressions of IL-17 cytokines and receptors. These results provide an insight into the roles of IL-17 in mediating inflammation and immunity.

Cell biology of ischemia/reperfusion injury

Disorders characterized by ischemia/reperfusion (I/R), such as myocardial infarction, stroke, and peripheral vascular disease, continue to be among the most frequent causes of debilitating disease and death. Tissue injury and/or death occur as a result of the initial ischemic insult, which is determined primarily by the magnitude and duration of the interruption in the blood supply, and then subsequent damage induced by reperfusion. During prolonged ischemia, ATP levels and intracellular pH decrease as a result of anaerobic metabolism and lactate accumulation. As a consequence, ATPase-dependent ion transport mechanisms become dysfunctional, contributing to increased intracellular and mitochondrial calcium levels (calcium overload), cell swelling and rupture, and cell death by necrotic, necroptotic, apoptotic, and autophagic mechanisms. Although oxygen levels are restored upon reperfusion, a surge in the generation of reactive oxygen species occurs and proinflammatory neutrophils infiltrate ischemic tissues to exacerbate ischemic injury. The pathologic events induced by I/R orchestrate the opening of the mitochondrial permeability transition pore, which appears to represent a common end-effector of the pathologic events initiated by I/R. The aim of this treatise is to provide a comprehensive review of the mechanisms underlying the development of I/R injury, from which it should be apparent that a combination of molecular and cellular approaches targeting multiple pathologic processes to limit the extent of I/R injury must be adopted to enhance resistance to cell death and increase regenerative capacity in order to effect long-lasting repair of ischemic tissues.

Higher infiltration by Th17 cells compared with regulatory T cells is associated with severe acute T-cell-mediated graft rejection

The aim of this study was to evaluate whether the Th17 and Treg cell infiltration into allograft tissue is associated with the severity of allograft dysfunction and tissue injury in acute T cell-mediated rejection (ATCMR). Seventy-one allograft tissues with biopsy-proven ATCMR were included. The biopsy specimens were immunostained for FOXP3 and IL-17. The allograft function was assessed at biopsy by measuring serum creatinine (Scr) concentration, and by applying the modified diet in renal disease (MDRD) formula, which provides the estimated glomerular filtration rate (eGFR). The severity of allograft tissue injury was assessed by calculating tissue injury scores using the Banff classification. The average numbers of infiltrating Treg and Th17 cells were 11.6 ± 12.2 cells/mm² and 5.6 ± 8.0 cells/mm², respectively. The average Treg/Th17 ratio was 5.6 ± 8.2. The Treg/Th17 ratio was significantly associated with allograft function (Scr and MDRD eGFR) and with the severity of interstitial injury and tubular injury (P < 0.05, all parameters). In separate analyses of the number of infiltrating Treg and Th17 cells, Th17 cell infiltration was significantly associated with allograft function and the severity of tissue injury. By contrast, Treg cell infiltration was not significantly associated with allograft dysfunction or the severity of tissue injury. The results of this study show that higher infiltration of Th17 cell compared with Treg cell is significantly associated with the severity of allograft dysfunction and tissue injury.

The NF-κB transcription factor c-Rel is required for Th17 effector cell development in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a T cell-mediated autoimmune disease involving effector Th subsets such as Th1 and Th17. In this study, we demonstrate that mice lacking the NF-κB transcription factor family member c-Rel (rel(-/-)), which are known to be resistant to EAE, show impaired Th17 development. Mixed bone marrow chimeras and EAE adoptive transfer experiments show that the deficiency of effector Th17 cells in rel(-/-) mice is T cell intrinsic. Consistent with this finding, c-Rel was activated in response to TCR signaling in the early stages of Th17 development and controlled the expression of Rorc, which encodes the Th17 transcription factor retinoic acid-related orphan receptor γt. CD28, but not IL-2, repression of Th17 development was dependent on c-Rel, implicating a dual role for c-Rel in modulating Th17 development. Adoptive transfer experiments also suggested that c-Rel control of regulatory T cell differentiation and homeostasis influences EAE development and severity by influencing the balance between Th17 and regulatory T cells. Collectively, our findings indicate that in addition to promoting Th1 differentiation, c-Rel regulates the development and severity of EAE via multiple mechanisms that impact on the generation of Th17 cells.

Inflammatory cytokines determine the susceptibility of human CD8 T cells to Fas-mediated activation-induced cell death through modulation of FasL and c-FLIP(S) expression

The nature of inflammatory signals determines the outcome of T cell responses. However, little is known about how inflammatory cytokines provided to human CD8 T cells during activation affects their susceptibility to post-activation cell death. We have examined and compared the effects of the inflammatory cytokine IL-12, as well as the combination of IL-1, IL-6, and IL-23 (IL-1/6/23) on the susceptibility of primary human CD8 T cells to post-activation cell death. Human CD8 T cells activated in the presence of IL-1/6/23 underwent significantly less cell death after activation as compared with those activated in IL-12. This was due to reduced susceptibility to Fas-mediated activation-induced cell death (AICD). Mechanistically, the reduced level of cell death in CD8 T cells activated in IL-1/6/23 was a result of a low level of FasL expression and high level of c-FLIP(S) expression. When the effect of IL-1, IL-6, and IL-23 individually was examined, IL-1 or IL-6 alone was sufficient to inhibit CD8 T cell death that occurs after activation in IL-12. IL-1, but not IL-6, inhibited expression of FasL, whereas IL-6, but not IL-1, increased c-FLIP(S) expression. Our findings show that the presence of IL-1 and/or IL-6 during activation of human CD8 T cells attenuates Fas-mediated AICD, whereas IL-12 increases the susceptibility of activated CD8 T cells to this form of cell death.