Programmed cell death protein 1 (PD1) deficiency induces cardiac inflammation during baseline conditions and ischemia/reperfusion injury

Background

The Programmed cell death protein 1 (PD1) immune checkpoint is densely expressed on cardiac endothelial cells. The increasing clinical application of immune checkpoint inhibitor therapy targeting PD1 for the treatment of advanced malignancies has revealed profound cardiovascular side effects that have recently paralleled in a preclinical model. However, the effects of PD1 deficiency during baseline conditions and myocardial injury are so far unknown.

Purpose

This study aims to assess the impact of PD1 deficiency on myocardia immunity, and to evaluate the relevance of PD1 signalling in cardiac disease.

Methods

C57BL/6J wild-type mice and C57BL/6J Pdcd1−/− mice were purchased and bred at the animal facility. In-vivo ischaemia/reperfusion (I/R) injury was applied to assess the response in cardiac injury. In brief, mice were anesthetised followed by lateral thoracotomy and ligation of the left coronary artery for 45 min. For flow cytometry, hearts were removed and subjected to an enzymatic digestion. Single cell solutions were stained with different antibody panels to assess cardiac immune cells and the expression of programmed cell death protein 1 ligand 1 (PDL1). Western blot was conducted after homogenization of snap-frozen heart tissue using specific primary and corresponding secondary antibodies. Immunofluorescence and conventional haematoxylin and eosin stain from 4 μm sections were used to visualize the distribution of PDL1 in cardiac tissue.

Results

While no overt cardiac phenotype was observed in Pdcd1−/− mice, a profound upregulation of pro-inflammatory cytokines was determined during baseline conditions, including interleukin (IL) 1α IL4, and extracellular-signal regulated kinase (ERK) 1/2. NADPH oxidase 1 (NOX1) which is involved in production of reactive oxygen species and endothelial injury response was downregulated in Pdcd1−/− mice. Following I/R injury, a significant decline in endothelial PDL1 expression was observed, which was attributed to changes in the area at risk, as shown by immunofluorescence staining. The infarct size following in-vivo I/R injury was not altered upon PD1-deficiency as determined by TTC staining. However, flow cytometry determined increased cell numbers of distinct leukocyte subsets during reperfusion-related inflammation.

Conclusion

Deficiency of PD1/PDL1 signalling shows distinct inflammatory changes in cardiac tissue at baseline and I/R injury. The results indicate that relevant PD1-related detrimental effects are not limited to complications from cancer therapy but can be expected in various forms of cardiovascular disease, hence requiring further investigations.

Funding Acknowledgement

Type of funding sources: Public hospital(s). Main funding source(s): Department of Cardiology and Vascular Medicine, West German Heart and Vascular Center, University Hospital Essen, Germany

Blockade of the innate immune checkpoint CD47 decreases infarct size by modulation of oxidative stress and immune response

Background

Myocardial infarction (MI) is the leading cause of death worldwide. Following ischemia/reperfusion (I/R) injury a precisely controlled immune response is necessary for preservation of cardiac integrity. In its course, immune cells interact with dead and damaged cells via a variety of cell surface molecules. One such interaction revolves around signal regulatory protein α (SIRPα) on myeloid cells and ubiquitously expressed CD47, which inhibits phagocytosis and was thus termed an innate immune checkpoint. Inhibition of CD47 via antibodies was shown to be protective in other I/R injury of eg liver and kidney, mostly by modulation of nitric oxide (NO) related pathways. Whether it is also beneficial in myocardial I/R injury remains to be seen.

Methods and results

We determined I/R injury size in murine hearts after anti-CD47 treatment using the triphenyl tetrazolium chloride (TTC)/Evans blue test and found decreased TTC negative per area at risk (AAR) at 24 h of reperfusion when compared to IgG antibody treated mice. Likewise ejection fraction was higher and plasma cardiac Troponin I (cTNI) levels were lower in anti-CD47 treated animals at the same time point. We further studied immune cell populations using flow cytometry, which revealed similar levels of neutrophils at 24 h of reperfusion in both anti-CD47 and control groups. To investigate this paradox, we deployed cutting edge light sheet fluorescence microscopy (LSFM) to simultaneously measure I/R injury size and immune cell levels and indeed found a higher ratio of neutrophils per injured area in CD47 treated mice. Furthermore, in these animals neutrophil populations were localized outside the injured area rather than only just inside, as was the case in the control group. We further measured cardiac reactive oxygen species (ROS) concentration and found ROS levels to be slightly decreased after CD47 injections following I/R. In contrast to results from other I/R injury models, we could not find an influence of anti-CD47 treatment on nitrate/nitrite/NO pathways.

Conclusion

Anti-CD47 treatment was shown to be protective in various I/R injury models. We could also demonstrate reduced infarct sizes after 24 h of reperfusion. This was not associated with decreased levels of neutrophils, which also located only outside of the injured area. Whether this is beneficial for the long term outcome, remains to be investigated. Nevertheless CD47 blockade presents as a highly novel and promising approach to AMI treatment and warrants further research.

Funding Acknowledgement

Type of funding sources: None.

P2557A novel tool for light sheet-guided analysis of myocardial injury in murine and human samples

Background

Cardiovascular diseases are the most prominent global health threats. For optimal treatment, myocardial biopsies are an indispensable requirement. Current analysis includes histological and biochemical assays with particular limits. Here we present a first approach utilizing light sheet fluorescence microscopy (LSFM) to visualize the 3D vasculatory architecture in the murine heart after experimental myocardial infarction (MI) and in human cardiac biopsies with simultaneously imaging of various immunological infiltrates for disease investigation.

Methods and results

For murine hearts, cardiac vasculature was stained using CD31-AF790 antibody, where we found distinct spots of negative staining, which correlated in size and localisation with other markers of cardiac damage such as triphenyl tetratzolium chloride (TTC) staining, ejection fraction (EF) reduction and plasma cardiac troponin I levels. Using a Ly6G-AF647 antibody, we were able to visualize neutrophil infiltrates 24 h after MI, which localized at the border of the I/R-injury zone. 5 d after MI we imaged the healing vasculatory network using the CD31 marker as well as infiltrated macrophages using F4/80 staining.

Human cardiac vasculature was stained using CD31-AF790 antibody in a whole-mount staining approach. In short, human samples were fixed in 4% PFA and permeabelized using saponin-based detergents. Antibody staining was conducted at 30 °C in the dark over several days. Immunological infiltrates were visualized using human CD66b, CD16, CD64, CD3 and CD19 antibodies in various, simultaneous approaches. After staining, cardiac samples were dehydrated and cleared using ethyl cinnamate (ECi) for light sheet microscopy. The spatial resolution of cardiac blood vessels was determined by CD31 staining, revealing a highly organized and structured vascular tree. Simultaneous staining for immunological infiltrates showed association with areas of enhanced CD31 staining, displaying activated endothelium at sites of inflammation.

Ly6G events in a murine heart

Conclusion

Light sheet-guided analysis of cardiac samples shows promising results in terms of synchronous vascular and immunological investigation. We highlighted its applicability in identifying specific immune cells based on immune-phenotyping. This novel technique may enable future clinical heart disease investigation with a powerful tool for visualization of 3D cardiac structure and identification of multiple immune cell infiltrates.

Effect of Concentration on the Interfacial and Bulk Structure of Ionic Liquids in Aqueous Solution

Bio and aqueous applications of ionic liquids (IL) such as catalysis in micelles formed in aqueous IL solutions or extraction of chemicals from biologic materials rely on surface-active and self-assembly properties of ILs. Here, we discuss qualitative relations of the interfacial and bulk structuring of a water-soluble surface-active IL ([C₈MIm][Cl]) on chemically controlled surfaces over a wide range of water concentrations using both force probe and X-ray scattering experiments. Our data indicate that IL structuring evolves from surfactant-like surface adsorption at low IL concentrations, to micellar bulk structure adsorption above the critical micelle concentration, to planar bilayer formation in ILs with <1 wt % of water and at high charging of the surface. Interfacial structuring is controlled by mesoscopic bulk structuring at high water concentrations. Surface chemistry and surface charges decisively steer interfacial ordering of ions if the water concentration is low and/or the surface charge is high. We also demonstrate that controlling the interfacial forces by using self-assembled monolayer chemistry allows tuning of interfacial structures. Both the ratio of the head group size to the hydrophobic tail volume as well as the surface charging trigger the bulk structure and offer a tool for predicting interfacial structures. Based on the applied techniques and analyses, a qualitative prediction of molecular layering of ILs in aqueous systems is possible.

Splenic Vein Thrombosis Following Pancreas Transplantation: Identification of Factors That Support Conservative Management

Prophylaxis for graft portal/splenic venous thrombosis following pancreas transplant varies between institutions. Similarly, treatment of venous thrombosis ranges from early re-exploration to conservative management with anticoagulation. We wished to determine the prevalence of graft splenic vein (SV) thrombosis, as well as the clinical significance of non-occlusive thrombus observed on routine imaging. Records of 112 pancreas transplant recipients over a 5-year period at a single center were reviewed. Venous thrombosis was defined as absence of flow or presence of thrombus identified in any part of the graft SV on ultrasound. Thirty patients (27%) had some degree of thrombus or absence of flow in the SV on postoperative ultrasound. There were 5 graft losses in this group. Four were due to venous thrombosis, and occurred within 20 days of transplant. All patients with non-occlusive partial SV thrombus but normal arterial signal on Doppler ultrasound were successfully treated with IV heparin followed by warfarin for 3-6 months, and remained insulin independent. Findings of arterial signal abnormalities, such as absence or reversal of diastolic flow within the graft, require urgent operative intervention since this finding can be associated with more extensive thrombus that may lead to graft loss.

OPTN/SRTR 2015 Annual Data Report: Early effects of the new kidney allocation system

In December 2014, a new kidney allocation system (KAS) was implemented in the United States in an attempt to improve access to transplant for historically underrepresented groups, and to incorporate longevity matching such that donor kidneys with the longest projected graft survival are given to recipients with the longest projected patient survival. The development of organ allocation policies is often guided by simulated allocation models, computer programs that simulate the arrival of donated organs and new candidates on the waiting list over a 1-year period to project outcomes under a new allocation method. We examined the early outcomes under the new KAS using quarterly data beginning in 2013, revealing whether trends were already underway before implementation. Quarterly data also serve to reveal any bolus effect, or a rapid rise or fall in the proportion of transplants in a given group due to reordering of the list, followed by tapering toward a new steady state. Post-KAS changes were notable for an increase in the proportion of transplants among younger candidates, black and Hispanic candidates, highly sensitized candidates, and those on dialysis for at least 5 years. Transplants among blood type B candidates increased slightly but these candidates remain underrepresented relative to their prevalence on the waiting list. Regional and national sharing increased under the new KAS, but transplants of kidneys with a kidney donor profile index above 85% decreased. Early graft survival appears unchanged, but given the increases in regional sharing, cold ischemia time, and transplants among highly sensitized candidates and candidates with long pretransplant dialysis time, long-term graft survival will need to monitored.

Liver Retransplantation in Patients With HIV-1 Infection: An International Multicenter Cohort Study

Liver retransplantation is performed in HIV-infected patients, although its outcome is not well known. In an international cohort study (eight countries), 37 (6%; 32 coinfected with hepatitis C virus [HCV] and five with hepatitis B virus [HBV]) of 600 HIV-infected patients who had undergone liver transplant were retransplanted. The main indications for retransplantation were vascular complications (35%), primary graft nonfunction (22%), rejection (19%), and HCV recurrence (13%). Overall, 19 patients (51%) died after retransplantation. Survival at 1, 3, and 5 years was 56%, 51%, and 51%, respectively. Among patients with HCV coinfection, HCV RNA replication status at retransplantation was the only significant prognostic factor. Patients with undetectable versus detectable HCV RNA had a survival probability of 80% versus 39% at 1 year and 80% versus 30% at 3 and 5 years (p = 0.025). Recurrence of hepatitis C was the main cause of death in the latter. Patients with HBV coinfection had survival of 80% at 1, 3, and 5 years after retransplantation. HIV infection was adequately controlled with antiretroviral therapy. In conclusion, liver retransplantation is an acceptable option for HIV-infected patients with HBV or HCV coinfection but undetectable HCV RNA. Retransplantation in patients with HCV replication should be reassessed prospectively in the era of new direct antiviral agents.

Ungewöhnliche Substitutionsreaktion von (σ-Allyl)manganpentacarbonyl mit 2.3-Bis(diphenylphosphino)-N-methylmaleinimid / Unusual Reaction of (σ-Allyl)manganesepentacarbonyl with Bis(diphenylphosphino)-N-methyl Maleic Anhydride

σ-C3H5 · Mn(CO)5 reacts with bis(diphenyl-phosphino)-N-methyl maleic anhydride to form a complex in which the C3H5-ligand migrates from the coordination sphere of Mn to the phosphine ligand. The high yield (70%) suggests that this reaction takes place within the coordination sphere of Mn. The product (X-ray analysis) shows unusual bonding properties.

Peginterferon and ribavirin for treatment of recurrent hepatitis C disease in HCV-HIV coinfected liver transplant recipients

Achievement of a sustained virologic response (SVR) with antiviral therapy significantly improves graft survival in hepatitis C virus (HCV) monoinfected liver transplant (LT) patients. Risks and benefits of HCV therapy in HCV-human immunodeficiency virus (HIV) coinfected LT recipients are not well established. Among 89 HCV-HIV LT recipients in the HIVTR cohort, 39 (23% Black, 79% genotype 1, 83% fibrosis stage ≤ 1) were treated with peginterferon-a2a or a2b plus ribavirin for a median 363 days (14-1373). On intent-to-treat basis, 22% (95% CI: 10-39) and 14% (95% CI: 5-30) achieved an end-of-treatment response (EOTR) and SVR, respectively. By per-protocol analysis (completed 48 weeks of therapy ± dose reductions), 42% and 26% had EOTR and SVR, respectively. Severe adverse events occurred in 85%, with 26% hospitalized with infections and 13% developing acute rejection. Early discontinuations and dose reductions occurred in 38% and 82%, respectively, despite use of growth factors in 85%. Eighteen of 39 treated patients (46%) subsequently died/had graft loss, with 10 (26%) attributed to recurrent HCV. In conclusion, SVR rates are low and tolerability is poor in HCV-HIV coinfected transplant recipients treated with peginterferon and ribavirin. These results highlight the critical need for better tolerated and more efficacious HCV therapies for HCV-HIV coinfected transplant recipients.

Isolation and hepatocyte differentiation of mesenchymal stem cells from porcine bone marrow--"surgical waste" as a novel MSC source

Mesenchymal stem cells (MSC) isolated from bone marrow and differentiated into hepatocyte-like cells have increasingly gained attention for clinical cell therapy of liver diseases because of their high regenerative capacity. They are available from bone marrow aspirates of the os coxae after puncture of the crista iliaca or from bone marrow "surgical waste" gained from amputations or knee and hip operations. Thus, the aim of the study was to demonstrate whether these pBM-MSC (porcine bone marrow-derived mesenchymal stem cells) displayed mesenchymal features and hepatocyte differentiation potential. MSC were isolated either from crista iliaca punctures or after sampling and collagenase digestion of bone marrow from the os femoris. Mesenchymal features were assessed by flow cytometry for specific surface antigens and their ability to differentiate into at least 3 lineages. Functional properties, such as urea or glycogen synthesis and cytochrome P450 activity, as well as the cell morphology were examined during hepatocyte differentiation. pBM-MSC from both sources lacked the hematopoietic markers CD14 and CD45 but expressed the typical mesenchymal markers CD44, CD29, CD90, and CD105. Both cell types could differentiate into adipocyte, osteocyte, and hepatocyte lineages. After hepatocyte differentiation, CD105 expression decreased significantly and cells changed morphology from fibroblastoid into polygonal, displaying significantly increased glycogen storage, urea synthesis, and cytochrome activity. pBM-MSC from various sources were identical in respect to their mesenchymal features and their hepatocyte differentiation potential. Hence, long bones might be a particularly useful resource to isolate bone marrow mesenchymal stem cells for transplantation.

Role of PD-L1 and PD-L2 in allergic diseases and asthma

Asthma is the result of chronic airway inflammation associated predominantly with CD4+ cells, eosinophils, mast cells, and basophils. Several T-cells subsets, including NKT cells, play a critical role in orchestrating the inflammation in the airways predominantly, by secreting interleukin-4 and interleukin-13. Recently, programmed death-1 (PD-1) with its ligands, programmed death ligand B7H1 (PD-L1) and B7DC (PD-L2), was shown to regulate T-cell activation and tolerance. PD-1 has been characterized as a negative regulator of conventional CD4+T cells. In addition, the relative roles of PD-L1 and PD-L2 in regulating the activation and function of T cells have recently been characterized. Recent studies have demonstrated that PD-L1 and PD-L2 have important but opposing roles in modulating and polarizing T-cell functions in airway hyperreactivity. Whereas the severity of asthma is greatly enhanced in absence of PD-L2, PD-L1 deficiency resulted in reduced airway hyperresponsiveness and only minimal inflammation. This observation is partially because of the polarization of NKT cells in PD-L1- and PD-L2-deficient mice. This review will discuss the recent literature regarding the role of PD-L1 and PD-L2 in allergic disease and asthma. Current understanding of the role of PD ligands in allergic asthma gives impetus to the development of novel therapeutic approaches.

PD-L1 and PD-L2 modulate airway inflammation and iNKT-cell-dependent airway hyperreactivity in opposing directions

Interactions of the inhibitory receptor programmed death-1 (PD-1) with its ligands, programmed death ligand (PD-L)1 and PD-L2, regulate T-cell activation and tolerance. In this study, we investigated the role of PD-L1 and PD-L2 in regulating invariant natural killer T (iNKT)-cell-mediated airway hyperreactivity (AHR) in a murine model of asthma. We found that the severity of AHR and airway inflammation is significantly greater in PD-L2(-/-) mice compared with wild-type mice after either ovalbumin (OVA) sensitization and challenge or administration of alpha-galactosylceramide (alpha-GalCer). iNKT cells from PD-L2(-/-) mice produced significantly more interleukin (IL)-4 than iNKT cells from control mice. Moreover, blockade of PD-L2 interactions of wild-type iNKT cells in vitro with monoclonal antibodies (mAbs) resulted in significantly enhanced levels of IL-4 production. In contrast, PD-L1(-/-) mice showed significantly reduced AHR and enhanced production of interferon-gamma (IFN-gamma) by iNKT cells. iNKT-deficient Jalpha18(-/-) mice reconstituted with iNKT cells from PD-L2(-/-) mice developed high levels of AHR, whereas mice reconstituted with iNKT cells from PD-L1(-/-) mice developed lower levels of AHR compared with control. As PD-L2 is not expressed on iNKT cells but rather is expressed on lung dendritic cells (DCs), in which its expression is upregulated by allergen challenge or IL-4, these findings suggest an important role of PD-L2 on lung DCs in modulating asthma pathogenesis. These studies also indicate that PD-L1 and PD-L2 have important but opposing roles in the regulation of AHR and iNKT-cell-mediated activation.

Treatment-dependent loss of polyfunctional CD8+ T-cell responses in HIV-infected kidney transplant recipients is associated with herpesvirus reactivation

Antiretroviral-therapy has dramatically changed the course of HIV infection and HIV-infected (HIV(+)) individuals are becoming more frequently eligible for solid-organ transplantation. However, only scarce data are available on how immunosuppressive (IS) strategies relate to transplantation outcome and immune function. We determined the impact of transplantation and immune-depleting treatment on CD4+ T-cell counts, HIV-, EBV-, and Cytomegalovirus (CMV)-viral loads and virus-specific T-cell immunity in a 1-year prospective cohort of 27 HIV(+) kidney transplant recipients. While the results show an increasing breadth and magnitude of the herpesvirus-specific cytotoxic T-cell (CTL) response over-time, they also revealed a significant depletion of polyfunctional virus-specific CTL in individuals receiving thymoglobulin as a lymphocyte-depleting treatment. The disappearance of polyfunctional CTL was accompanied by virologic EBV-reactivation events, directly linking the absence of specific polyfunctional CTL to viral reactivation. The data provide first insights into the immune-reserve in HIV+ infected transplant recipients and highlight new immunological effects of thymoglobulin treatment. Long-term studies will be needed to assess the clinical risk associated with thymoglobulin treatment, in particular with regards to EBV-associated lymphoproliferative diseases.

Hepatic progenitor cells from adult human livers for cell transplantation

OBJECTIVE

Liver regeneration is mainly based on cellular self-renewal including progenitor cells. Efforts have been made to harness this potential for cell transplantation, but shortage of hepatocytes and premature differentiated progenitor cells from extra-hepatic organs are limiting factors. Histological studies implied that resident cells in adult liver can proliferate, have bipotential character and may be a suitable source for cell transplantation.

METHODS

Particular cell populations were isolated after adequate tissue dissociation. Single cell suspensions were purified by Thy-1 positivity selection, characterised in vitro and transplanted in immunodeficient Pfp/Rag2 mice.

RESULTS

Thy-1(+) cells that are mainly found in the portal tract and the surrounding parenchyma, were isolated from surgical liver tissue with high yields from specimens with histological signs of regeneration. Thy-1(+) cell populations were positive for progenitor (CD34, c-kit, CK14, M2PK, OV6), biliary (CK19) and hepatic (HepPar1) markers revealing their progenitor as well as hepatic and biliary nature. The potential of Thy-1(+) cells for differentiation in vitro was demonstrated by increased mRNA and protein expression for hepatic (CK18, HepPar1) and biliary (CK7) markers during culture while progenitor markers CK14, chromogranin A and nestin were reduced. After transplantation of Thy-1(+) cells into livers of immunodeficient mice, engraftment was predominantly seen in the periportal portion of the liver lobule. Analysis of in situ material revealed that transplanted cells express human hepatic markers HepPar1 and albumin, indicating functional engraftment.

CONCLUSION

Bipotential progenitor cells from human adult livers can be isolated using Thy-1 and might be a potential candidate for cell treatment in liver diseases.

Human albumin preserves islet mass and function better than whole serum during pretransplantation islet culture

OBJECTIVE

Human islet transplant protocols frequently include a brief period of islet culture before transplantation. Some investigators have suggested that medium supplementation with human serum might quench collagenase activity and provide better culture conditions when compared with human albumin. We studied the effect of whole serum on islet count, islet equivalence, insulin secretion, and DNA content in human islets.

METHODS

Adult human islets isolated from a single pancreas with purity >50% were cultured in identical 150 islet equivalent samples at 37 degrees C using CMRL 1066-based islet medium (Mediatech) supplemented with either 0.5% human albumin or 10% human AB serum. Prior to culture and after 3 days, islets were assessed in vitro using dithizone staining (n = 4), insulin release after static glucose stimulation (n = 8), and DNA content (n = 8).

RESULTS

After 3 days, islet mass (defined by the number of islets and islet equivalents counted after dithizone staining) was better preserved in islets cultured in 0.5% human albumin. Although the stimulation index and total DNA content were similar between groups, islets cultured in human albumin demonstrated greater absolute insulin secretion (p = .02) and insulin secretion per cell (p = .02).

CONCLUSIONS

When used to supplement CMRL 1066-based islet culture medium, human albumin preserves islet mass and secretory capacity better than whole human serum. Human serum offers no advantage in islet preservation or function.

Tract-based spatial statistics of diffusion tensor imaging in adults with dyslexia

BACKGROUND AND PURPOSE

Diffusion tensor imaging is a tool that can be used to study white matter microstructure in dyslexia. We tested the hypothesis that dyslexics have a white matter structural change (as measured by directional diffusion of water, which can be affected by disruption in white matter tracts) between brain regions that previous functional connectivity studies showed were associated with phonologic processing.

MATERIALS AND METHODS

Diffusion tensor imaging (DTI) scans were acquired from 7 healthy adult normal readers and from 14 adults with dyslexia on a 1.5T scanner. Voxelwise statistical analysis of the fractional anisotropy data were carried out by using Tract-Based Spatial Statistics to compare dyslexic subjects versus control subjects in white matter tracts.

RESULTS

Significant group difference map clusters (comparing adults with and without dyslexia) occurred in specific bilateral white matter tracts within the frontal lobe, temporal lobe, occipital lobe, and parietal lobe.

CONCLUSION

The DTI fractional anisotropy results in the bilateral white matter showing higher fractional anisotropy in adult control subjects compared with adults with dyslexia (relating to white matter fiber tract integrity) are consistent with our previous functional connectivity results from seed points in the bilateral inferior frontal gyrus.

T-cell co-stimulatory molecules: their role in allergic immune reactions

The development of allergic diseases, such as allergic asthma, depends upon the initiation and maintenance of T-helper cell type-2-skewed allergen-specific immune reactions. Although it is clear that susceptibility to this process is under genetic and environmental control, the fine-tuning and regulation of the type-2 T-helper cell immune response is not yet fully understood. In this second article in the present series, current understanding regarding the involvement of T-cells and antigen-presenting cells is summarised, with emphasis on the interaction between these two types of immune regulatory cells by means of co-stimulatory molecules.

Sequence characterization and expression patterns of defensin and lysozyme encoding genes from the gut of the reduviid bug Triatoma brasiliensis

The cDNAs encoding an intestinal defensin (def1) and lysozyme (lys1) of the reduviid bug Triatoma brasiliensis have been amplified by PCR using specific oligonucleotide primers and 5'- and 3'-RACE, cloned and sequenced. The 576 bp clone has an open reading frame of 282 bp and encodes a pre-prodefensin with 94 amino acid residues, containing a putative signal and activation peptide cleavage site at Ser19 and Arg51, respectively. The genomic DNA contains a second defensin gene with similar characteristics, 88.3% identity and also one intron of 107 nucleotides. The 538 bp clone has an open reading frame of 417 bp, encoding a pre-lysozyme with 139 amino acid residues. The putative signal peptide is cleaved at alanine 18. Using whole mount in situ hybridization, high expression of both genes has been found, distributed uniformly throughout the entire cardia and the blood-storing stomach and to a much lower extent in the digesting small intestine. Using quantitative real-time PCR, the expression level of def1 was also shown to be very low in small intestine, rectum and salivary glands; in the stomach, expression was 500-2500 times higher than in the cardia and fat body. No expression of lys1 could be detected in the salivary glands and rarely a very low expression in the small intestine, rectum and fat body. Lys1 expression in the stomach was 60-300 times higher than in the cardia. Comparing the levels in unfed fifth instars and up to 15 days after feeding, a strong def1 induction was evident in the fat body at 15 days after feeding and in the stomach a maximum level of def1 and lys1 at 5 days after feeding.

Pretransplant islet culture: a comparison of four serum-free media using a murine model of islet transplantation

INTRODUCTION

Human islet transplant protocols frequently incorporate a brief period of islet culture before transplantation. The optimal medium for pretransplant islet culture is unknown.

METHODS

We compared four serum-free media formulated for human islets: Miami (MM1), Memphis (M-SFM), Edmonton (EDM), and hCell OCZEM-SF/AF (hCell). Islets isolated from a single human pancreas with purity >80% were cultured in 2500-islet-equivalent (IE) fractions using the media listed. After 7 days, each 2500-IE fraction was grafted under the kidney capsule of a streptozocin-diabetic rag1 mouse (n = 4 per group). Mice were evaluated with serum glucose monitoring, stimulated C-peptide release, and glucose tolerance tests. Islet fractions transplanted immediately after isolation (n = 4 mice) served as controls. In vitro islet function was assessed on days 0 and 3 and included insulin release (after static glucose stimulation), total cellular C-peptide content, cell count, and viability.

RESULTS

Glucose control was improved in all cohorts of mice after transplant, but only islet grafts cultured in MM1 were statistically indistinguishable from fresh islets. MM1- and hCell-cultured islet grafts showed improved glucose tolerance compared with fresh islets; C-peptide release was similar among the four cohorts. In vitro, only islets cultured in MM1 had similar stimulation index to fresh islets, whereas only hCell- and MM1-cultured islets demonstrated recovery of C-peptide content and insulin release.

CONCLUSIONS

Media choice before transplant can influence islet quality, even when culture periods are short. Miami MM1 and hCell media may provide better islet protection than alternative media.

Resiquimod, a new immune response modifier from the family of imidazoquinolinamines, inhibits allergen-induced Th2 responses, airway inflammation and airway hyper-reactivity in mice

BACKGROUND

Allergen-induced sensitization and airway disease are the results of adverse immune reactions against environmental antigens that may be prevented or inhibited by immune modifying strategies.

OBJECTIVE

To investigate the effects of the novel immune response modifier resiquimod (R-848), from the family of imidazol-derivates, in a murine model of allergen-mediated Th2-immune responses and concomitant airway inflammation and airway hyper-reactivity.

METHODS

BALB/c mice were systemically sensitized with ovalbumin (OVA) on days 1 and 14 and challenged with OVA aerosol on days 28 and 29. R-848 was applied intranasally to sensitized animals once prior to the first allergen airway challenge, on day 27.

RESULTS

A single application of R-848 significantly reduced numbers of eosinophils and lymphocytes in bronchoalveolar lavage fluid and inhibited mucus gland hyperplasia, compared with sensitized and challenged controls. Associated with the decrease in airway inflammation, single intranasal treatment with R-848 abolished the development of airway hyper-reactivity after allergen sensitization and airway challenges. Additionally, Th2-cytokine production in lung tissues from sensitized and R-848-treated animals was reduced, whereas IL-12 and IFN-gamma production was increased, compared with non-treated sensitized mice.

CONCLUSION

These data indicate that R-848 effectively inhibits allergen-induced airway inflammation and hyper-reactivity by modulation of increased Th2-immune responses.

Intraoperative fluid management of living donor versus cadaveric liver transplant recipients

Living donor liver transplantation has increasingly become an alternative to cadaveric donor liver transplants for select adult patients. Because these cases can be performed electively, living donor recipients may have better compensated liver disease at the time of surgery than cadaver donor recipients. However, it is unknown if this difference would have a significant effect on their intraoperative course. Therefore, we compared the intraoperative fluid management of patients receiving liver grafts from either living or cadaveric donors (n = 25, each group). Patient groups did not differ in demographics or baseline laboratory values. The duration of anesthesia and anhepatic phases were significantly longer in living donor cases (651 +/- 80 minutes vs 409 +/- 20 and 55 +/- 14 vs 45 +/- 6, P < .05). Adjusted for anesthesia time and patient weight, fluid administration (crystalloid and albumin) was not different between the two groups. Intraoperative transfusion requirements were also not significantly different in recipients from living donors versus cadaveric donors with regard to red blood cells, fresh frozen plasma, platelets, and cryoprecipitate. However, arterial oxygenation was better preserved in recipients from living donors. The PaO2/FiO2 (P/F) ratio at the end of the procedure was significantly better in patients receiving livers from living rather than from cadaveric donors (P/F ratio 335 +/- 114 mm Hg vs 271 +/- 174, P < .05). Our results indicate that while intraoperative fluid and transfusion requirements are similar, the impact of transplantation on pulmonary gas exchange is more pronounced in patients receiving organs from cadaveric donors. This difference may arise from longer cold ischemia times present in the cadaveric donor group.

Experience with steroid-free maintenance immunosuppression in simultaneous pancreas-kidney transplantation

INTRODUCTION

Steroid avoidance is possible in simultaneous pancreas-kidney transplantation with the use of newer immunosuppressive agents and induction therapy. We undertook a retrospective consecutive case review of patients treated at a university tertiary referral center.

METHODS

Medical records of 44 consecutive patients receiving a pancreas-kidney transplant from November 2000 to September 2002 were reviewed. The immunosuppression protocol used in this series of patients consisted of thymoglobulin induction, combined with mycophenolate mofetil, tacrolimus, and sirolimus for maintenance immunosuppression. Steroids were used only while thymoglobulin was given and were typically discontinued by postoperative week 1. Main outcome measures included graft and patient survival rates, rejection rates of the kidney or pancreas, infection rates, and surgical complication rates.

RESULTS

All 44 patients received a kidney-pancreas transplant with systemic venous anastomosis and enteric drainage of the pancreas. Patient kidney, and pancreas survival rates were 95.6%, 93.2%, and 88.7%, respectively. Biopsy-proven pancreas rejection rates at 1 and 6 months posttransplant were 2.3% and 2.3%. Kidney rejection rates at 1 and 6 months were 2.3% and 4.6%. Reasons for patient loss included one death from sepsis and one cardiovascular death. Reasons for kidney loss besides death included a thrombotic microangiopathy. Reasons for pancreas loss included three thromboses, one mild rejection/infection, and one duodenal segment leak with infection. All patients who have been free of rejection have been off steroids for the duration of follow-up.

CONCLUSIONS

Newer immunosuppression protocols without maintenance steroids are possible with minimal rejection in the first 3 months and equivalent patient and graft survival rates compared with earlier protocols utilizing steroids. The potential beneficial long-term impact of steroid avoidance will require further study.

Alterations in skeletal muscle structure are minimized with steroid withdrawal after renal transplantation

BACKGROUND

Limitations in exercise capacity in kidney transplant recipients are thought to result in part from changes in muscle structure and function associated with immunosuppression therapy.

METHODS

We compared the percent distribution of skeletal muscle fiber types, cross-sectional areas, and ultrastructural morphologies in kidney transplant recipients treated with standard prednisone maintenance therapy (n=21) to those undergoing rapid withdrawal of prednisone using Simulect (interleukin 2 receptor inhibitor) (n=13). Skeletal muscle biopsy specimens from the vastus lateralis were analyzed at 3 and 12 months after transplantation and compared with sedentary controls (n=15).

RESULTS

Compared with the control group, the group receiving prednisone maintenance therapy had a significantly lower percentage of type I fibers and a higher percentage of type IIB/x fibers, evident at 3 and 12 months. Fiber type distribution in patients withdrawn from prednisone did not differ from controls. In patients withdrawn from prednisone, the cross-sectional areas of type I and IIA fibers were lower and the area of type IIB/x fibers was higher compared with controls. Likewise, ultrastructural studies revealed reduced volume densities of myofibrils and higher densities of interfibrillar and subsarcolemmal mitochondria. At 12 months there were no ultrastructural differences between the patients withdrawn from prednisone and controls.

CONCLUSIONS

We conclude that prednisone maintenance therapy contributes to the lower exercise capacity by altering the ratio of type I to type IIB/x fibers and by reducing myofilament density. The increase in mitochondria in patients receiving prednisone may reflect a switch from carbohydrate to lipid metabolism resulting from the glucocorticoid therapy.

Health-related fitness and quality of life following steroid withdrawal in renal transplant recipients

BACKGROUND

Exercise capacity increases significantly soon after transplantation; however, over time it does not further improve and patients remain low compared to normal levels. The limitations to exercise following transplantation have not been identified, but may be related to immunosuppression therapy regimens that include prednisone.

METHODS

We studied health-related fitness measures (cardiorespiratory fitness, muscle strength, and body composition) and quality of life in renal transplant recipients randomized into two groups: those using standard maintenance immunosuppression, including prednisone therapy (N = 14); and those undergoing rapid withdrawal of steroids using Simulect[interleukin-2 (IL-2) receptor inhibitor] (N = 9). Testing was done at 3 and 12 months following transplant and the 12-month data were compared to 15 normal sedentary controls.

RESULTS

Compared to those maintained on steroids, the steroid withdrawal group showed greater gains in VO2peak (P = 0.05) and quadriceps peak torque (P = 0.05) and greater gains in the vitality score and the Physical Composite Scale on the SF-36 questionnaire (P < 0.05). At 1 year, all patients had significantly lower exercise capacity compared to the sedentary controls (P = 0.01). No differences were observed in body composition, with both patient groups increasing in body weight (primarily body fat) over time. At 12 months, all patients were not different in body fat percentage compared to the sedentary controls.

CONCLUSION

We conclude that prednisone is not the cause for increased body fat following transplantation; however, it may contribute to lower spontaneous improvements in exercise capacity possibly by limiting increases in muscle strength. The low exercise capacity in all transplant recipients studied at 1 year suggests a need for exercise training to optimize physical functioning following transplant.

De novo use of sirolimus in immunosuppression regimens in kidney and kidney-pancreas transplantation at the University of California, San Francisco

At UCSF, we have used sirolimus in several immunosuppression regimens and protocols, and this article will summarize our experience in four areas. The purpose of the first study was to assess the efficacy of a sirolimus-based, calcineurin inhibitor-free regimen for the first 3 months after transplantation. Patients were treated with a calcineurin inhibitor-free regimen that consisted of daclizumab, sirolimus, mycophenolate mofetil (MMF), and conventional corticosteroids. Of nine patients, one (case #7) had an acute rejection episode (type IA) at 2 months after transplantation, which was fully reversed with corticosteroids. The second study was a prospective trial of calcineurin inhibitor-free regimen in patients with severe delayed graft function (DGF) (requiring dialysis). The immunosuppression regimen consisted of daclizumab, sirolimus, MMF, and corticosteroids. This immunosuppressive regimen was effective in patients with DGF; however, it was effective only in non-African American (non-AA) patients (AA had a significantly higher acute rejection rate at 1 year than non-AA, 63% vs 23%, P =.025). In some patients sirolimus was associated with a prolonged recovery from DGF. The addition of sirolimus to immunosuppressive agents provide the opportunity for safe steroid withdrawal (at day 5). We participated in a sirolimus-based, multicenter open-label trial of very early corticosteroid withdrawal. Primary renal transplant patients were enrolled in an immunosuppression regimen that consisted of basiliximab, sirolimus (target levels 8 to 15 ng/mL, 0 to 5 months, and 6 to 12 ng/mL, 6 to 12 months) and tacrolimus in a dose of 0.05 mg/kg BID (target levels 6 to 9 ng/mL). Two of 14 enrolled patients had an episode of acute rejection before steroids were withdrawn. No acute rejection episodes have occurred after steroids were withdrawn (6-month follow-up). The regimen of sirolimus and tacrolimus was well tolerated. Wound complications were not noted. Another important use of sirolimus has been its incorporation in the immunosuppressive regimens in kidney-pancreas transplantation. Our current protocol consists of thymoglobulin induction, combined with MMF, sirolimus, and low-dose tacrolimus, for maintenance therapy. Steroids are only utilized during the first 5 to 6 days following the transplant. This steroid-free maintenance regimen has been used in the last 30 enteric-drained, simultaneous pancreas-kidney transplants. Using this immunosuppressive approach, rejection rates are less than 10% for either the kidney or the pancreas.

Evidence for primary genetic determination of heart rate regulation: chromosomal mapping of a genetic locus in the rat

BACKGROUND

We investigated whether an accelerated heart rate (HR), observed in the stroke-prone spontaneously hypertensive rat (SHRSP(HD)), is a primary, genetically determined trait and whether it contributes to blood pressure (BP) regulation in this model of polygenic hypertension.

METHODS AND RESULTS

We measured BP and HR in SHRSP(HD) and normotensive Wistar-Kyoto rats (WKY), as well as in F2 hybrids bred from crossing the two strains, at baseline and after 12 days of dietary NaCl loading. Random marker genome screening and cosegregation analysis were performed on F2 hybrids derived from SHRSP(HD)/WKY-0(HD) (n=115) and SHRSP(HD)/WKY-1(HD) (n=139) crosses (WKY-0(HD) and WKY-1(HD) are two congenic WKY strains). HR in SHRSP(HD) was significantly higher than in WKY-0(HD) both at baseline (404+/-30 versus 375+/-46 bpm; P=.0034) and after NaCl (437+/-23 versus 364+/-40 bpm; P=10(-9)). BP in F2 hybrids showed no significant correlation with HR either at baseline or after NaCl loading. HR after NaCl loading but not at baseline was significantly linked in a recessive fashion to a locus on chromosome 3: in animals homozygous for the SHRSP(HD) allele, HR was 414+/-49 compared with 383+/-44 bpm in heterozygotes and WKY homozygotes (F(210,1)=19.7, P=1.4x10(-5), lod score=5.9). The putative BP-relevant gene at this locus, termed HR-SP1, showed no evidence of linkage to any of the BP parameters measured.

CONCLUSIONS

Our results demonstrate that a genetic locus on rat chromosome 3, HR-SP1, contributes directly to the regulation of HR in SHRSP(HD) but exhibits no effect on BP. Thus, in addition to its modulation by reflex-mediated neurohumoral mechanisms, HR is also under the direct influence of primary genetic factors.

The Y chromosome. Epistatic and ecogenetic interactions in genetic hypertension

Previous studies have revealed conflicting evidence concerning a Y-chromosome effect on blood pressure (BP) in genetic crosses involving different strains of spontaneously hypertensive rats (SHR or SHRSP). We had previously found an approximately 16 mm Hg difference in systolic BP (P < 10(-7)) at baseline but not after dietary salt loading (P = .82) between F2 males derived from an SHRSPHD grandfather and a Wistar-Kyoto (WKYHD-0) grandmother and F2 males from a reciprocal cross (WKYHD-0 grandfather). When we examined F2 animals from reciprocal crosses between SHRSPHD and a congenic strain, WKYHD-1, which carries a 6-centimorgan-long SHRSPHD-homologous genomic fragment on chromosome 10 that contains a quantitative trait locus linked to BP (BP/SP-la), we found no significant differences either at baseline (P = .39) or after salt loading (P = .51) in the two reciprocal F2 cohorts. To test the hypothesis that Y-chromosome-autosomal epistasis accounts for the discrepant Y-chromosome effects on BP, we analyzed the interaction between BP/SP-1a and reciprocal cross status on BP in the two crosses. In the F2 (WKYHD-0xSHRSPHD) cross, no significant interaction was found for basal systolic BP (P = .89), arguing against a major influence of BP/SP-1a on the Y-chromosome effects on basal BP. However, a significant interaction between zygosity at the BP/SP-1a locus and reciprocal cross status for systolic BP after salt loading (P = .022) indicated that the BP/SP-1a-SHRSPHD allele exhibited a significant effect on BP after dietary excess salt only in males that inherited the SHRSP Y chromosome. These results support the relevance of a Y-chromosome effect on BP and suggest that a complex interplay of epistatic and ecogenetic interactions governs its effect on phenotype.

Decreased mortality from technical failure improves results in pediatric liver transplantation

BACKGROUND

Until recently, pediatric liver transplantation was associated with a high rate of technical failure, which contributed substantially to the overall prognosis.

OBJECTIVE

To assess the impact of technical failure on outcome in pediatric liver transplantation.

DESIGN AND SETTING

We retrospectively analyzed 90 pediatric transplant procedures in a university medical center.

PATIENTS

Between February 1988 and December 1995, 80 children ( < 15 years old) received 90 transplants. Fifty-three percent (n = 42) were less than 2 years of age, 45% (n = 36) had cholestatic liver disease, 26% (n = 21) had metabolic errors, and 11% (n = 9) had fulminant hepatitis.

INTERVENTION

Patients underwent grafting using previously reported techniques, including cadaveric whole (61% [n = 55]), reduced-size (17% [n = 15]), and living related (22% [n = 20]) liver transplantation.

MAIN OUTCOME MEASURES

Patient and graft survival and selected surgical complications. Outcomes were compared before (group 1) and after (group 2) the introduction of living related transplantation in July 1992.

RESULTS

In group 1, 32 patients received 36 grafts (4 retransplants [13%]), and in group 2, 48 patients received 54 grafts (6 retransplants [13%]). Six- and 12-month patient survival rates were 78% (n = 25) and 75% (n = 24), respectively, for group 1 and 98% (n = 47) and 94% (n = 45) for group 2. Of the 9 deaths in group 1, 6 occurred early as a consequence of surgical complications, while in group 2, all 5 deaths that occurred were caused by the consequences of immunosuppression (lymphoproliferative disease, n = 2; late infections, n = 3).

CONCLUSIONS

These results suggest that mortality caused by surgical complications has been reduced by improvement in management in recent years. Living related grafts have supplemented the graft supply and may be associated with the improved overall results. Despite these advances, children receiving transplants continue to experience the consequences of imperfect immunosuppression.

A multicenter analysis of the first experience with FK506 for induction and rescue therapy after pancreas transplantation

Between May 1, 1993 and April 5, 1995, 154 pancreas allograft recipients at 9 institutions were given FK506 posttransplant. Three groups were studied: (1) recipients given FK506 initially for induction and maintenance therapy (n = 82), (2) recipients switched to FK506 for antirejection or rescue therapy (n = 61), and (3) recipients converted to FK506 for other reasons (n = 11). Of 82 patients in the induction group, 7 (9%) had simultaneous bone marrow (BM) and pancreas-kidney (SPK-BM) transplants, 54 (66%) had SPK transplants without BM, 14 (17%) had pancreas transplants alone (PTA), and 7 (9%) had pancreas after previous kidney transplants (PAK). All but 1 recipient was given quadruple immunosuppression (anti-T cell agents plus azathioprine and prednisone) for induction. The median FK506 starting dose was 4 mg/day p.o.; the median average FK506 blood level, 12 ng/ml. The most common side effects were neurotoxicity (16%), nephrotoxicity (13%), and gastrointestinal toxicity (9%). New-onset diabetes mellitus requiring permanent insulin therapy did not occur. Of 61 transplants in the rescue group, 44 (72%) were SPK, 11 (18%) PTA, and 6 (10%) PAK. All but 3 (95%) of the recipients had been on cyclosporine-azathioprine-prednisone triple immunosuppression before substitution of FK506 for cyclosporine; 46% of the recipients had one, and 54% > or = 2, rejection episodes preconversion. The most common side effects were nephrotoxicity (25%), neurotoxicity (23%), and gastrointestinal toxicity (21%). Two recipients were reconverted to cyclosporine because of transient hyperglycemia, and one recipient is on insulin. In the induction group, patient survival at 6 months was 90% for SPK, 100% for PTA, and 100% for PAK. According to a matched-pair analysis, pancreas graft survival for SPK recipients at 6 months was 87% for FK506 versus 70% for cyclosporine recipients (P = 0.04); for PTA recipients, 84% versus 66% (P = n.s.); and for PAK recipients, 80% versus 14% (P = 0.11). When technical failures and death with functioning grafts were censored, pancreas graft survival remained significantly better in the FK506 group. The incidence of first reversible rejection episodes by 6 months in FK506 recipients was 35% for SPK, 40% for PTA, and 20% for PAK. Of 75 pancreas grafts, 64 are currently functioning; in 5 recipients the pancreas failed (1 from rejection); 6 recipients died with a functioning pancreas graft. There were 3 posttransplant lymphomas (all EBV-positive); 2 recipients died and 1 is alive after subtotal colectomy and transplant pancreatectomy. In the antirejection rescue group, patient survival rates at 6 months were 91% for SPK, 100% for PTA, and 80% for PAK (P = n.s.). Pancreas graft survival rates at 6 months were 90% for SPK, 72% for PTA, and 40% for PAK. The incidence of first reversible rejection episodes after conversion to FK506 at 6 months was 44% in SPK, 54% in PTA, and 50% in PAK. Of 61 pancreas grafts, 51 are currently functioning; in 7 recipients the pancreas failed (5 from rejection); 3 recipients died with a functioning graft. There were no posttransplant lymphomas in the rescue group. This multicenter survey shows that FK506 in pancreas transplantation is associated with (1) a low rate of graft loss from rejection when used for induction therapy, (2) a high rate of graft salvage when used for rescue or rejection therapy, and (3) a very low rate of new-onset insulin-dependent diabetes mellitus. These encouraging results are tarnished by 3 posttransplant lymphomas in the induction group; a possible explanation is overimmunosuppression, but further (randomized) studies are necessary to analyze the long-term risk-benefit ratio of FK506 after pancreas transplantation.

Clinical islet transplantation experience of the University of California Islet Transplant Consortium

BACKGROUND

The University of California Islet Transplant Consortium was formed to evaluate the feasibility of performing clinical islet transplantation at different transplant centers by using a single centralized islet isolation laboratory.

METHODS

From July 1992 through February 1995 seven adult islet transplantations were performed, six allografts and one autograft. Once procured, human pancreata were brought to the UCLA-VA Islet Core Laboratory for islet isolation and purification, which were then transported to different centers for transplantation. Patients 1 through 3 received their transplants in Los Angeles, patient 4 received her islet transplant in Torrance, and patients 5 through 7 received their transplants in San Francisco.

RESULTS

Although none of these patients achieved insulin independence, four of seven had functioning grafts longer than 6 months as indicated by circulating C-peptide level greater than 0.7 ng/ml. Furthermore, improved glucose control as shown by a decreased insulin requirement was seen in 57% (four of seven patients) of these patients. The ability to isolate islets at a single laboratory and transport them long distances to different centers was shown in patients 4 through 7.

CONCLUSIONS

Islet transplantation can be performed with improvements in blood glucose control, and islets can be isolated at a centralized location and successfully transported to different centers for transplantation.

Local renin-angiotensin systems in cardiovascular tissues: localization and functional role

In its classical definition, the renin-angiotensin system (RAS) acts predominantly by endocrine mechanisms. This view has been modified since several components of the RAS and their mRNAs were found in peripheral tissues. These findings gave rise to the concept of local tissue renin-angiotensin systems. Although no cells of cardiovascular organs containing a complete RAS have been identified as of this writing, angiotensinogen and angiotensin-converting enzyme (ACE) are most likely synthesized within the vasculature for example. Local synthesis of renin may be limited to very small amounts, but uptake of renin from the circulation is very likely. The function of local RASs is shown by reduction of blood pressure by ACE inhibitors, which correlates better with the inhibition of ACE activity in certain tissues than with its activity in the plasma. Further studies have put forward the notion that the circulating RAS could mainly be important for acute hemodynamic stability, whereas the tissue RAS could be involved in more long term maintenance of hemodynamics. This review will try to summarize the findings leading to the concept of a local tissue renin-angiotensin system, and discuss interactions between the circulating and the local RAS in the light of recent experimental findings.