Lymphocyte homing to allografts

Hepatic sinusoidal endothelium avidly binds platelets in an integrin-dependent manner, leading to platelet and endothelial activation and leukocyte recruitment

Platelets have recently been shown to drive liver injury in murine models of viral hepatitis and promote liver regeneration through the release of serotonin. Despite their emerging role in inflammatory liver disease, little is known about the mechanisms by which platelets bind to the hepatic vasculature. Therefore, we referenced public expression data to determine the profile of potential adhesive receptors expressed by hepatic endothelium. We then used a combination of tissue-binding and flow-based endothelial-binding adhesion assays to show that resting platelets bind to human hepatic sinusoidal endothelial cells and that the magnitude of adhesion is greatly enhanced by thrombin-induced platelet activation. Adhesion was mediated by the integrins Gp1b, αIIbβIII, and αvβ3, as well as immobilized fibrinogen. Platelet binding to hepatic endothelial cells resulted in NF-κB activation and increased chemokine secretion. The functional relevance of platelet binding was confirmed by experiments that showed markedly increased binding of neutrophils and lymphocytes to hepatic endothelial cells under shear conditions replicating those found in the hepatic sinusoid, which was in part dependent on P-selectin expression. Thus the ability of platelets to activate endothelium and promote leukocyte adhesion may reflect an additional mechanism through which they promote liver injury.

Genetic Predisposition and Renal Allograft Failure

Renal allograft rejection or dysfunction often results in graft failure, and remains the major obstacle in the success of renal transplantation. Various immunological and nonimmunological factors are involved in allograft rejection. In addition to human leukocyte antigen loci, several genetically controlled molecules have been identified in recent years as playing important roles in the process of rejection. Genetic variants in genes encoding different T-helper (Th) type 1 and Th2 cytokines, chemokines and their receptors, growth factors, molecules of the renin-angiotensin system, enzymes of the homocysteine pathway, and proteins acting as substrates of immunosuppressive drugs impact on the success of engraftment and highlight the concept of genetic predisposition to allograft rejection. This review evaluates specific genetic variants and their functional roles in graft failure, with an emphasis on the latest methodologies available for genotyping, and appropriate strategies to enable them to become a tool of predictive and individualized medicine to ensure better transplant outcome.

Immune factors influencing ethnic disparities in kidney transplantation outcomes

An influence of ethnicity on the outcomes of kidney transplant recipients has been recognized for several decades. Both immune and nonimmune factors have been explored as potential explanations. Most studies have focused on the inferior outcomes of African-Americans. As a group, African-Americans differ from Caucasians with respect to a number of measurable components of the alloimmune response, including the T-cell repertoire and the expression and function of costimulatory molecules and various cytokines and chemokines. In general, these differences suggest that African-Americans may be high immune responders. However, no single difference in any of these components of alloimmunity satisfactorily explains the disparities in outcomes. It seems probable that some combination of immune factors interacts with nonimmune factors, such as socioeconomic resources, to influence transplant outcomes in a complex manner.

Inhibition of allogeneic inflammatory responses by the Ribonucleotide Reductase Inhibitors, Didox and Trimidox

Background

Graft-versus-host disease is the single most important obstacle facing successful allogeneic stem cell transplantation (SCT). Even with current immunosuppressive therapies, morbidity and mortality rates are high. Current therapies including cyclosporine A (CyA) and related compounds target IL-2 signaling. However, although these compounds offer great benefit, they are also associated with multiple toxicities. Therefore, new compounds with a greater efficacy and reduced toxicity are needed to enable us to overcome this hurdle.

Methods

The allogeneic mixed lymphocyte reaction (MLR) is a unique ex vivo method to study a drug's action on the initial events resulting in T-cell activation and proliferation, synonymous to the initial stages of tissue and organ destruction by T-cell responses in organ rejection and Graft-versus-host disease. Using this approach, we examined the effectiveness of two ribonucleotide reductase inhibitors (RRI), Didox and Trimidox, to inhibit T-cell activation and proliferation.

Results

The compounds caused a marked reduction in the proliferative responses of T-cells, which is also accompanied by decreased secretion of cytokines IL-6, IFN-γ, TNF-α, IL-2, IL-13, IL-10 and IL-4.

Conclusions

In conclusion, these data provide critical information to justify further investigation into the potential use of these compounds post allogeneic bone marrow transplantation to alleviate graft-versus-host disease thereby achieving better outcomes.

Association of MCP-1 and CCR2 polymorphisms with the risk of late acute rejection after renal transplantation in Korean patients

Among the factors modulating transplant rejection, chemokines and their respective receptors deserve special attention. Increased expression of monocyte chemoattractant protein-1 (MCP-1) and its corresponding receptor (chemokine receptor-2, CCR2) has been implicated in renal transplant rejection. To determine the impact of the MCP-1-2518G and CCR2-64I genotypes on renal allograft function, 167 Korean patients who underwent transplantation over a 25-year period were evaluated. Genomic DNA was genotyped using polymerase chain reaction followed by restriction fragment length polymorphism analysis. Fifty-five (32.9%) patients were homozygous for the MCP-1-2518G polymorphism. Nine (5.4%) patients were homozygous for the CCR2-64I polymorphism. None of the investigated polymorphism showed a significant shift in long-term allograft survival. However, a significant increase was noted for the risk of late acute rejection in recipients who were homozygous for the MCP-1-2518G polymorphism (OR, 2.600; 95% CI, 1.125–6.012; P = 0.022). There was also an association between the MCP-1-2518G/G genotype and the number of late acute rejection episodes (P = 0.024). Although there was no difference in the incidence of rejection among recipients stratified by the CCR2-V64I genotype, recipients with the CCR2-V64I GG genotype in combination with the MCP-1-2518G/G genotype had a significantly higher risk of acute or late acute rejection among the receptor-ligand combinations (P = 0.006, P = 0.008, respectively). The MCP-1 variant may be a marker for risk of late acute rejection in Korean patients.

Cyclosporine inhibits mouse cytomegalovirus infection via a cyclophilin-dependent pathway specifically in neural stem/progenitor cells

The potential of neural stem and progenitor cell (NSPC) transplantation in neurodegenerative disease raises a concern about immunosuppressive agents and opportunistic neurotropic pathogens that may interfere with engraftment. Cytomegalovirus (CMV) is an important opportunistic pathogen infecting the central nervous system, where it may remain latent for life, following transplacental transmission. Cyclosporine (Cs), an immunosuppressive drug used in organ transplantation, where its use is associated with CMV reactivation, suppressed murine CMV (MCMV) infection in cultured NSPCs but not in fibroblasts. This activity of Cs appears to be mediated via cyclophilin (CyP) rather than via calcineurin. First, the calcineurin-specific inhibitor FK506 failed to suppress replication. Second, the CyP-specific inhibitor NIM811 strongly suppressed replication in NSPC. NSPCs maintained in the presence of NIM811 retained viral genomes for several weeks without detectable viral gene expression or obvious deleterious effects. The withdrawal of NIM811 reactivated viral replication, suggesting that the inhibitory mechanism was reversible. Finally, inhibition of endogenous CyP A (CyPA) by small interfering RNA also inhibited replication in NSPCs. These results show that MCMV replication depends upon cellular CyPA pathways in NSPCs (in a specific cell type-dependent fashion), that CyPA plays an important role in viral infection in this cell type, and that inhibition of viral replication via CyP leads to persistence of the viral genome without cell damage. Further, the calcineurin-signaling pathway conferring immunosuppression in T cells does not influence viral replication in a detectable fashion.

Low molecular weight fucan prevents transplant coronaropathy in rat cardiac allograft model

INTRODUCTION

Transplant arteriosclerosis is the main cause of long-term failure after cardiac transplantation. Vascular rejection is thought to be due to intimal proliferation occurring in response to arterial wall immune-mediated injury. A low molecular weight fucan (LMWF) compound, a sulfated polysaccharide, has been demonstrated to increase plasma levels of stromal cell-derived factor 1 (SDF-1) and consequently to mobilize bone marrow-derived vascular progenitor cells (BMVPC). The aim of this study was to evaluate the capacity of LMWF to prevent coronary intimal proliferation in a rat cardiac allograft model.

METHODS

Heterotopic abdominal cardiac graftings were performed in Brown Norway (BN) and Lewis (LEW) rats. Animals were divided into 4 groups of 10 rats. Two groups were treated intramuscularly with LMWF (5 mg/kg/day) (one BN to BN isograft group, and one BN to LEW allograft group); and two control groups were LMWF-untreated (one BN to BN isograft group and one BN to LEW allograft group). All animals were treated by cyclosporin (15 mg/kg/day) sub-cutaneously and sacrificed at day 30. The cardiac grafts were assessed by morphometry of structural parameters and by histological and immunohistochemical analyses.

RESULTS

All cardiac isografts were devoid of any coronary and parenchymal lesions. In contrast, the majority of untreated allografts developed coronary intimal proliferation in close association with intimal and adventitial inflammatory CD68(+) cell infiltration. Further, the parenchyma exhibited large areas of actin(+) cells (myofibroblasts) of recipient origin colocalized with the CD68(+) infiltrating cells. Interestingly, all LMWF-treated allografts were well protected against coronary and parenchymal lesions and the coronary arteries exhibited an intimal monolayer of flat cells, which however were CD34 negative.

CONCLUSION

treatment with LMWF appeared very effective in this rat cardiac allograft model to prevent arterial and parenchymal lesions occurring in response to alloimmune injury. However this protective effect does not appear to depend on mobilization of bone marrow-derived cells.

Duffy antigen receptor and genetic susceptibility of African Americans to acute rejection and delayed function

BACKGROUND

The unique distribution of the alleles for the Duffy antigen receptor complex (DARC) that binds to chemokines may be associated with the rates of acute rejection and delayed allograft function (DGF) among African Americans.

METHODS

A prospective, multicenter cohort study enrolled 222 African American recipients of cadaveric renal allografts from eight adult transplant centers. Subjects were typed by allele-specific polymerase chain reaction (ASPCR) for the polymorphism at position 535 that determines the level of transcription. Associations of DARC genotypes were examined in Cox hazards models with episodes of acute rejection and in logistic regression models with the development of DGF.

RESULTS

FyB Null homozygosity was observed among 67% of the recipients. Fifteen percent of the study cohort experienced at least one episode of acute rejection, and the incidence of DGF was 42.5%. The number of FyB Null alleles and FyB Null homozygosity had no detectable association with the rate of acute rejection (P > 0.50) or with the development of DGF (P > 0.50).

CONCLUSION

The susceptibility of African American recipients to acute rejection and to DGF was not confirmed to be associated with DARC alleles or genotype. Future studies should exclude a potential role of donor-related DARC in transplant outcomes.

In vitro treatment of dendritic cells with tacrolimus: impaired T-cell activation and IP-10 expression

BACKGROUND

High doses (10(-6)-10(-8) M) of tacrolimus (FK506) were reported to induce a type-2 T-helper cell (Th2)-promoting function in developing dendritic cells (DC). We used a therapeutic dose (2.4 x 10(-9 )M) of tacrolimus to investigate its effect on human monocyte-derived DC.

METHODS

Using untreated and treated immature and mature DC we compared T cell-activating capacity, surface marker expression, T cell and DC cytokine profile and transcription of genes coding for a panel of DC function-related molecules.

RESULTS

Tacrolimus-treated mature DC had reduced T-cell stimulatory capacity. Although interleukin (IL)-12 production of DC was impaired, they did not promote Th2 development as T cells activated by tacrolimus-treated DC produced less interferon (IFN)-gamma, IL-4 and IL-10. The up-regulation of the T-cell activation marker CD69 and the production of IL-2 were impaired. In addition, tacrolimus-treated DC produced less IP-10 (CXCL10), which is known to be involved in allograft rejection. Other molecules related to DC function remained unchanged.

CONCLUSIONS

Tacrolimus treatment reduces the ability of DC to stimulate T cells and the impaired production of DC-derived IP-10 (CXCL10) and IL-12 might play a role in the immunosuppressive action of tacrolimus.

A Monocyte chemoattractant protein-1 (MCP-1) polymorphism and outcome after renal transplantation

Among the factors modulating transplant rejection and cardiovascular disease, chemokines and their respective receptors deserve special attention. In this respect, increased expression of MCP-1 and the corresponding receptor CCR2 have been demonstrated in renal transplant rejection and coronary artery disease. The impact of the MCP-1-2518G and CCR2-64I genotypes on renal allograft function was investigated in 232 patients who underwent transplantation over an 11-yr period. Genomic DNA was genotyped using PCR with sequence-specific primers followed by restriction fragment length polymorphism analysis. Eighteen (7.8%) patients were homozygous for the MCP-1-2518G mutation. The G/G allele of MCP-1 -2518 behaved as a determinant for long-term allograft survival and resulted in reduction of the mean graft survival, as compared with the heterozygous (A/G) or wild-type (A/A) allele (67 +/- 14 versus 95 +/- 4 mo; Log rank P = 0.0052). The 64I mutation of CCR2 had no effect on kidney graft failure (93 +/- 6 and 91 +/- 5 mo, respectively; P = 0.81). None of the investigated polymorphisms showed a significant shift in gene frequency in acute rejection and rejection-free groups. In conjunction with these findings, peripheral blood mononuclear cells from kidney transplant recipients carrying the G-allele were characterized by a 2.5-fold higher MCP-1 secretion (P < 0.05). In conclusion, recipients of renal transplants homozygous for the -2518 G mutation of the MCP-1 gene are at risk for premature kidney graft failure. This variant of MCP-1 may be a future predictor for long-term kidney graft failure.

A model for reactivation of CMV from latency

BACKGROUND

Reactivation of CMV from latency results in serious morbidity and mortality in immunocompromised transplant recipients. The mechanism by which CMV reactivates from latency has not been well understood.

OBJECTIVE

In this review we discuss three models for reactivation from latency and present evidence in favor of the model that reactivation is a multi-step process which is initiated by the allogeneic response to the transplanted organ. Study design (J. Virol. 75 (2001) 4814). Mice latently infected with murine cytomegalovirus (MCMV) were used as donors for allogeneic or syngeneic kidney transplants into immunocompetent recipients. The contralateral donor kidneys were used as controls. Transplanted kidneys were removed at various times after transplant and analyzed for expression of viral genes associated with productive infection and for expression of inflammatory cytokines. Electrophoretic mobility shift assay was performed on nuclear extracts of control and transplanted kidneys to examine activation of AP-1 and NFkappaB. Latently infected mice were also injected with tumor necrosis factor (TNF) to examine the effect of TNF alone on induction of MCMV immediate-early (IE) gene expression. Transgenic major immediate early promoter-lacZ mice carrying a beta-galactosidase reporter gene under the control of the human cytomegalovirus (HCMV) IE promoter/enhancer were used as donors for allogeneic kidney transplants to study the effect of allogeneic transplantation on induction of HCMV IE gene expression.

RESULTS

Allogeneic, but not syngeneic transplantation induces MCMV IE-1 expression and expression of inflammatory cytokines, including TNF. Allogeneic transplantation activates transcription factors, including NFkappaB and AP-1. TNF alone can induce MCMV IE-1 gene expression and activation of NFkappaB and AP-1 in some tissues.

CONCLUSIONS

We propose that induction of IE-1 gene expression is the first step in reactivation of the virus in an immunocompromised transplant recipient, and that it occurs as a result of the allogeneic response, which induces expression of TNF and subsequent activation of NFkappaB, and ischemia/reperfusion injury, which induces activation of AP-1. We speculate that the natural stimulus for reactivation in an immunocompetent host is an inflammatory immune response to infection and that allogeneic transplantation mimics this process.

Epstein-Barr virus infection is associated with endothelial Bcl-2 expression in transplant liver allografts

INTRODUCTION

In liver transplant recipients with Epstein-Barr virus (EBV) disease, we reported a low rate of acute rejection after stopping or markedly lowering immunosuppression. This observation led to the hypothesis that EBV, as a means of viral persistence, induces expression of antiapoptotic factors and these factors, in turn, confer protection to the transplanted organ. Bcl-2, an antiapoptotic factor induced by EBV in various host cells, is not normally expressed in the liver. We questioned whether bcl-2 is expressed in the transplanted liver and whether its expression is modified by EBV.

MATERIALS AND METHODS

Retrospective liver biopsy specimen from liver transplant patients diagnosed with EBV (n=12) were examined for the presence of bcl-2 by immunohistochemistry and compared with EBV (-) transplant (n=15), and nontransplant (n=13) livers.

RESULTS

The most significant finding was the presence of endothelial bcl-2 expression in the majority of EBV (+) transplant samples examined (67%) and its relative absence in the other two groups (P<0.005). There was also bcl-2 expression in the hepatocytes and lymphocytes of the majority of transplant liver samples, irrespective of EBV status.

DISCUSSION

We have identified a strong association between EBV infection and endothelial bcl-2 expression in transplant livers. We also found that transplantation, in itself, was associated with bcl-2 expression in the hepatocytes and lymphocytes of liver allografts.

New approaches to immunosuppression in liver transplantation

With the continued improvements in outcome following liver transplantation, the drawbacks associated with conventional immunosuppression regimens become increasingly apparent. Although up to 70% of patients develop a histological infiltrate of the graft (acute rejection), many of these will resolve spontaneously, and chronic rejection is rare. If a robust form of allograft acceptance or tolerance can be established, then immunosuppression can be withdrawn along with all the accompanying risks. The liver is already known to be associated with downregulated immune responses; the mechanism for this is unclear, but may be related to a number of mechanisms known to be involved in peripheral tolerance. There are many strategies being studied for achieving allograft tolerance, including the use of modern immunosuppressants, antibodies that target key molecules in the immune response, and recruitment of leukocytes to allografts. In the interim, it is necessary to look for safe protocols that allow trials of tolerance strategies without putting patients at increased risk.

Differential expression of chemokines and chemokine receptors shapes the inflammatory response in rejecting human liver transplants

BACKGROUND

Graft rejection after liver transplantation is associated with a lymphocytic infiltrate, the nature of which will be determined by, among various factors, the local activity of chemokines that attract particular subsets of effector cells to the graft.

METHODS

The expression of chemokines and receptors in human liver allografts was studied by immunohistochemistry of tissue and flow cytometry of blood and liver-derived lymphocytes. Receptor function was assessed with in vitro chemotaxis.

RESULTS

We report increased expression of chemokine receptors CXCR3, CXCR4, and CCR5 on circulating and graft-infiltrating lymphocytes after liver transplantation. Liver-derived T cells responded to the ligands for these receptors in vitro, which suggests that the receptors are functionally active. The chemokine ligands for these receptors were detected in rejecting allografts. CXCR3 ligands interferon-inducible protein 10 and monokine-induced by gamma interferon were detected on sinusoidal endothelium and interferon-inducible T-cell alpha chemoattractant was detected on portal and hepatic vascular endothelium, whereas the CXCR4 ligand, stromal-derived factor (SDF), was restricted to biliary epithelium. CCR5 ligands have previously been shown on portal endothelium. An in vitro model of T-cell alloactivation demonstrated a similar pattern of expression of functional CXCR3, CXCR4, and CCR5 on T cells. Increased expression of chemokine receptors, especially CCR3 and CCR5, was associated with redistribution of activated Kupffer cells in rejecting grafts.

CONCLUSIONS

The patterns of chemokine expression in liver allografts during rejection suggest that the recruitment and positioning of lymphocytes is mediated by specific chemokines. Although ligands for the receptors CXCR3 and CCR5 are important for recruitment, the restriction of SDF to bile ducts suggests that CXCR4 may be involved in the retention of alloactivated lymphocytes at sites of graft damage.

Donor-derived IP-10 initiates development of acute allograft rejection

An allograft is often considered an immunologically inert playing field on which host leukocytes assemble and wreak havoc. However, we demonstrate that graft-specific physiologic responses to early injury initiate and promulgate destruction of vascularized grafts. Serial analysis of allografts showed that intragraft expression of the three chemokine ligands for the CXC chemo-kine receptor CXCR3 was induced in the order of interferon (IFN)-gamma-inducible protein of 10 kD (IP-10, or CXCL10), IFN-inducible T cell alpha-chemoattractant (I-TAC; CXCL11), and then monokine induced by IFN-gamma (Mig, CXCL9). Initial IP-10 production was localized to endothelial cells, and only IP-10 was induced by isografting. Anti-IP-10 monoclonal antibodies prolonged allograft survival, but surprisingly, IP-10-deficient (IP-10(-/-)) mice acutely rejected allografts. However, though allografts from IP-10(+/+) mice were rejected by day 7, hearts from IP-10(-/-) mice survived long term. Compared with IP-10(+/+) donors, use of IP-10(-/-) donors reduced intragraft expression of cytokines, chemokines and their receptors, and associated leukocyte infiltration and graft injury. Hence, tissue-specific generation of a single chemokine in response to initial ischemia/reperfusion can initiate progressive graft infiltration and amplification of multiple effector pathways, and targeting of this proximal chemokine can prevent acute rejection. These data emphasize the pivotal role of donor-derived IP-10 in initiating alloresponses, with implications for tissue engineering to decrease immunogenicity, and demonstrate that chemokine redundancy may not be operative in vivo.