Biomedical subjects

Anthony N Warrens

Publications and source records attributed to Anthony N Warrens.

17 recordsLinked to original sources

PubMed2007

Fas ligand exerts its pro-inflammatory effects via neutrophil recruitment but not activation.

Fas ligand (FasL) expression induces apoptosis of activated T cells and has been suggested as a strategy to inhibit graft rejection. Unfortunately, the use of FasL to confer 'immune privilege' in this setting has been hampered by the finding that it may also provoke a destructive granulocytic response. While the Fas/FasL-mediated apoptotic pathways are well defined, the pro-inflammatory effects of FasL are poorly understood. Our aim in this study was to define in vitro the biological effects of FasL on neutrophil recruitment and activation. DAP-3 cells expressing human FasL on the cell membrane (mFasL) potently induced apoptosis in human neutrophils and in activated T lymphocytes. Recombinant human soluble FasL (sFasL), by contrast, was a very weak inducer of apoptosis, even at high concentrations. This latter observation suggests that cleavage of mFasL by naturally occurring matrix metalloproteinases may serve to down-regulate FasL activity in vivo. However, in the presence of a cross-linking antibody, the efficiency of apoptosis-induction by sFasL was greatly increased, suggesting that the lesser pro-apoptotic potency of sFasL reflects an inability to induce trimerization of the Fas receptor. With regard to pro-inflammatory effects, we found that sFasL is a potent neutrophil chemoattractant and, given that it induces little apoptosis, the dominance of sFasL over mFasL may mean that graft-infiltrating neutrophils will survive to mediate inflammation. Neither sFasL nor mFasL produced neutrophil activation as assessed by chemiluminescence assay. This suggests that neutrophils recruited to an inflammatory site by FasL will be activated by mechanisms other than Fas-FasL signalling.

Animals↗

PubMed2005

Cyclosporine A does not alter ultrasonic indices of renal blood flow: a potential tool for differentiating toxicity from acute rejection?

The narrow therapeutic window of cyclosporine A (CsA) means its use is controlled by pharmacokinetic monitoring. However, pharmacokinetics do not always reflect the functional effects of a drug--its pharmacodynamics, such as vasoconstriction. We developed a technique for measuring renal blood flow and used a pig model to determine whether CsA-induced renal vasoconstriction could be detected, thus offering a tool for pharmacodynamic therapeutic drug monitoring. This has been shown to differentiate acute rejection from acute tubular necrosis. Power Doppler intensitometry was used to assess relative vascular volume, and the renal arteriovenous transit time was determined with an intravenous microbubble bolus. Measurements were taken before and at intervals after an intravenous bolus of CsA (10 mg/kg). There was no correlation between index and CsA concentration. Lack of detectable effect after CsA administration to high concentrations suggests that this technique may be able to differentiate CsA toxicity from acute rejection.

Animals↗

PubMed2005

Chorea associated with thyroxine replacement therapy.

Chorea is an uncommonly reported manifestation of hyperthyroidism. We report the first description of generalized chorea due to iatrogenic thyrotoxicosis and propose that the movement disorder is due to a direct effect of thyroxine on the basal ganglia rather than being an autoimmune phenomenon.

Aged↗

PubMed2005

Attitudes toward transplantation in U.K. Muslim Indo-Asians in west London.

The worldwide shortage of organs for transplantation makes it important to understand why some oppose donation. Attitudes vary with religion and ethnicity. Accordingly, we undertook a qualitative study of the attitudes of 141 U.K. Muslim Indo-Asians to organ donation. Participants were observed, focus group discussions held and in-depth individual interviews conducted. We identified a high level of alienation from the health care system in general. With respect to organ donation in particular, its importance was generally discounted, often in deference to authority figures within the community who appeared negatively disposed. The culture-specific issues arguing against donation included a sense of the sacredness of the body, a fatalistic approach to illness, a belief that organs took on an independent role as 'witnesses' to an individual's life on Judgement Day and an anxiety that the donor would have no control of the probity of the recipient of an organ. We believe these data suggest a need to improve in a culturally sensitive fashion the provision of health information provided to this community.

Asian People↗

PubMed2005

Achieving permanent survival of islet xenografts by independent manipulation of direct and indirect T-cell responses.

Recent success in pancreatic islet allotransplantation has raised expectations but has equally highlighted the acute shortage of donor tissue. The use of xenogeneic tissue would help to address this shortage; however, strong cellular immunity limits the application of this approach. T-cell responses to xenogeneic tissues involve recognition of intact species-mismatched major histocompatibility complex (MHC) molecules, the direct pathway, and xenogeneic proteins presented as peptides by responder-type MHC molecules, the indirect pathway. In this study, we exploited the species difference to selectively and sequentially inhibit direct and indirect xenoresponses after transplantation of porcine islets into mice. Selective inhibition of the direct response was achieved using porcine CTLA4-Ig, which binds preferentially to pig versus mouse B7 molecules. Selective inhibition of the indirect response was achieved using murine CTLA4-Ig, which binds preferentially to mouse B7 molecules. Administration of porcine CTLA4-Ig alone caused modest prolongation of islet survival. Injection of murine CTLA4-Ig alone had a minimal effect. However, the injection of the porcine fusion protein early and the murine homolog late after grafting led to permanent survival of the porcine islets, in the absence of any other immunosuppression. These results suggest that a similar approach could have clinical utility in porcine islet xenotransplantation.

Abatacept↗

PubMed2004

The neutrophil: the unnoticed threat in xenotransplantation?

BACKGROUND: Xenotransplantation offers one way to circumvent the widening gap between the demand for and supply of human organs for transplantation, and the pig is widely regarded as the donor animal most likely to prove appropriate. Most attention has focused on the adaptive immune response to xenogeneic tissue. However, there is optimism that it may soon be possible to overcome that hurdle. In this paper, we consider the possibility of the direct recognition of xenogeneic tissue by neutrophils. METHODS: We studied in vitro the interaction of human neutrophils with cultured porcine endothelial cells in assays of adhesion (both static and flow), activation on the basis of chemiluminescence, and diapedesis and chemotaxis using split-well chambers. RESULTS: Human neutrophils showed increased adhesiveness to porcine endothelium in both static and flow adhesion systems. While this did not activate the neutrophils at rest, in the presence of suboptimal concentrations of a parallel stimulus, phorbol myristate acetate, the interaction of human neutrophils with porcine endothelium caused a much greater respiratory burst than their interaction with controls. In addition, they showed greater diapedesis through porcine endothelium. Of greatest interest is the observation that porcine endothelium secretes a molecule that is chemotactic for human neutrophils. CONCLUSIONS: On the basis of these observations, we should consider the potential for neutrophil-mediated low-grade damage to xenografts emerging as a significant problem when others have been circumvented.

Animals↗

PubMed2004

Skewing of pretransplant anti-HLA class I antibodies of immunoglobulin G isotype solely toward immunoglobulin G1 subclass is associated with poorer renal allograft survival.

Sensitized patients with lymphocytotoxic immunoglobulin (Ig)G anti-human leukocyte antigen (HLA) antibodies have an increased risk of rejection and poorer graft survival. Little is known, however, about the correlation between IgG antibody subclass and clinical outcomes. We identified 20 sensitized renal transplant recipients (panel reactive antibody >15%), all of whom had anti-HLA class I antibodies of an IgG isotype with known specificity before transplantation but who received a crossmatch negative graft. We analyzed the degree of skewing solely toward IgG1 (n=11) or to other IgG subclasses with or without IgG1 (n=9) and correlated these findings with graft survival. At last follow-up (median follow-up 28 months), 6 of 11 patients (55%) with anti-HLA antibodies skewed toward IgG1 had lost their grafts compared with 0 of 9 patients (0%) with anti-HLA antibodies not skewed toward IgG1 (P =0.01 log-rank test). Anti-HLA antibodies of an IgG1 subclass may be a novel marker predicting poor graft outcome.

Adult↗

PubMed2004

Developing a porcine transplantation model: efficient gene transfer into porcine vascular cells.

BACKGROUND: The pig is generally regarded as likely to be the preferred donor animal in xenotransplantation. Although many hurdles remain to be cleared, it would be useful to be able to manipulate porcine endothelium genetically, among other reasons, to test approaches in the modulation of inflammation. However, as a nondividing cell, it is less easy to manipulate. METHODS: The authors performed in vivo and in vitro gene transfection experiments using as an adjunct the DNA-binding agent 4',6'-diamidino-2-phenylindole (DAPI), which protects DNA from degradation. RESULTS: The introduction of DAPI into a liposomal transfection system was able to increase in vitro transfection efficiency of both endothelial and vascular smooth muscle cells from the pig, even in the presence of small amounts of serum. This last observation encouraged the authors to use this system in vivo in porcine carotid arteries. In this model, the authors were also able to demonstrate a high degree of transfection efficiency using DAPI, which seemed to work by protecting DNA from degradation. CONCLUSIONS: The authors believe this technique may allow them to address many biological questions relating to intervening in vascular disease, inflammation, and immune responses in the context of transplantation and beyond.

Animals↗

PubMed2004

Will transplantation of kidneys from donors with blood group A2 into recipients with blood group B help British Indo-Asian patients with renal failure?

Despite a high incidence of renal failure, disproportionately fewer Indo-Asians in the United Kingdom receive a renal transplant, in part because of the high prevalence of blood group B. It is now clear that it is possible to safely transplant kidneys from donors with blood group A of the subtype A2 into recipients with blood group B if the latter have low titers of anti-A antibodies. We measured the anti-A titers in 25 Indo-Asian patients on dialysis being considered for transplantation and found stably low titers in all. Titers were comparable to those found in a control white population with blood group B. In addition, in a complement-dependent cytotoxicity crossmatch against group A lymphocytes, the only positive results were obtained in those with high preexisting panel reactivity (i.e., because of the presence of preformed anti-human leukocyte antigen antibodies). We conclude that there are grounds for investigating this approach further to solve the ethnic disparity in rates of transplantation.

ABO Blood-Group System↗

PubMed2003

Cellular and molecular themes in apoptosis.

Apoptosis, an active mechanism of cell death, is of central importance in many biological scenarios. Research in this area has the potential to contribute to our understanding of many diseases and raises several potential therapeutic opportunities. Given this potential and the speed with which our understanding of this field has advanced over recent years, it is timely to introduce the clinician to the background on which the clinical implications of this research will be built. This review begins with contrasting apoptosis with the other mechanism of cell death, necrosis, and then outlines the features by which apoptosis may be recognised. With a view to understanding the level at which this process may be involved in disease and therapeutics, it is important to be aware of the basic mechanistic features of the induction and execution of apoptosis. In this, surface molecules such as CD95 (Fas) and the cascade of intracellular enzymes involved at many levels in apoptosis, the caspases, are of central importance. In all this, the mitochondrion is crucial to the induction of apoptosis and the regulation of the whole process. In the last part of this review, we attempt to draw out the clinical relevance of all this information. It is clear that apoptosis has an important role in the pathophysiology of malignancy, particularly with respect to haematological cancers, but also other oncological diseases. Apoptosis is also very important in autoimmune disease and viral infection. Finally, it is clear that apoptosis may be manipulated therapeutically to the benefit of patients in various scenarios. This is clearly an exciting area for future development, but one which clearly depends on a thorough mechanistic understanding.

Antibodies, Monoclonal↗

PubMed2003

Role of duplex Doppler sonography in diagnosis of acute allograft dysfunction-time to stop measuring the resistive index?

Measurement of vascular resistive index (RI) by duplex Doppler sonography (DDS) has been proposed as a non-invasive technique to detect the presence of acute rejection in renal allograft recipients. Our aim was to evaluate the clinical utility of this technique. From 107 patients we reviewed 159 biopsies that were performed from 1993 to 2001 for the investigation of acute allograft dysfunction. Histological findings were correlated with RI measurements by contemporaneously performed DDS. The majority of biopsies were carried out within the first 3 months post-transplantation (111/159). Sixty-eight biopsies showed acute rejection, 91 biopsies had findings other than rejection (acute tubular necrosis, CyA toxicity, recurrent GN). Using a threshold mean RI value of 0.9, the test had a specificity for acute rejection of 89%, but a sensitivity of just 6%. If the threshold was lowered the sensitivity rose, but specificity declined sharply. Average RI in the rejection group was not higher than in controls (0.73+/-0.11 vs 0.74+/-0.11, respectively). We conclude that measurement of RI by DDS does not contribute to the diagnosis of acute allograft dysfunction.

Acute Disease↗

PubMed2003

Immunologic monitoring.

The development of reliable in vitro assays that could allow the quantitation and characterization of anti-donor alloimmune responses has always been a goal in clinical transplantation, both to predict presensitization to the transplanted tissue and to be able to identify rejection without resorting to more invasive tests. With recent development in our understanding of transplantation biology and therapeutics, there is a real expectation that these tests may be used to identify tolerance as much as to predict rejection. The traditional limiting dilution assays still have a contribution to make and are being complemented by an array of tools, such as ELISpot, flow cytometry-based techniques, and microarray analysis. The assays that have been informative, to date, are discussed in this review. This information will lead, at least, to a better understanding of how and when the rejection process occurs. More interestingly, the objective is to apply this information to evaluate tolerance-inducing strategies or to identify patients that have become tolerant to their graft and can be weaned of immunosuppression. Of course sensitive, accurate and specific immunologic monitoring has applications well beyond the field of transplantation.

Antigens↗

PubMed2003

On the horizon: tailor-made immunosuppression in renal transplantation.

Immunosuppression for renal transplantation has undergone more changes over the last 8 years than at any other time in its history. It is now possible to be more selective in the matching of drugs with a given patient. This brings with it the option of improving graft outcome and also minimizing adverse effects. It is an ongoing process that will utilize agents working at different points in the activation cascade of the CD4+ 'helper' T lymphocyte. It may also be possible to manipulate the immune system such that the organ-specific immune response may be switched off, or rendered 'tolerant', thus removing the need for any immunosuppressive drugs. In this brief review, we shall address each of these approaches and discuss other therapeutic avenues being investigated.

Humans↗

PubMed2002

A role for the Fas/Fas ligand apoptotic pathway in regulating myeloid progenitor cell kinetics.

Bone marrow from wild-type mice and mice with mutated Fas (lpr) or mutated Fas ligand (gld) was used to investigate the role of the Fas/FasL system in the regulation of myeloid progenitor cell kinetics.Granulocyte-macrophage colony-forming cells (CFU-GM) were measured by a standard colony assay and the proliferative activity of CFU-GM was measured by replating primary colonies and observing secondary colony formation. Fas expression was restored to lpr mouse bone marrow cells by retrovirus-mediated gene transfer and gld mouse marrow cells were treated with soluble FasL. Wild-type marrow cells were treated with YVAD (a caspase inhibitor) or anti-Fas monoclonal antibodies. There were greater frequencies of myeloid progenitor cells (CFU-GM) in lpr and gld mouse marrow compared to wild-type (WT) marrow (p = 0.0008). The proliferative capacity of CFU-GM was also significantly greater for lpr and gld CFU-GM compared to WT CFU-GM (p = 0.0003 and 0.0001, respectively). Retrovirus-mediated restoration of Fas into lpr marrow, and provision of soluble FasL (sFasL) to gld CFU-GM reduced CFU-GM proliferation to WT levels. Treatment of WT CFU-GM with YVAD or anti-FasL monoclonal antibody increased CFU-GM proliferation to the levels found in lpr and gld CFU-GM. YVAD significantly increased and anti-Fas significantly reduced the proliferative capacity of human CFU-GM (p = 0.015 and 0.04, respectively).Fas, FasL, and caspase activation may play an important role in regulating myeloid progenitor cell kinetics.

Animals↗

PubMed2002

Porcine mononuclear cells adhere to human fibronectin independently of very late antigen-5: implications for donor-specific tolerance induction in xenotransplantation.

To combat the shortage of donor organs, transplantation across species barriers has been proposed. Induction of tolerance would overcome the substantial immunologic barriers to xenotransplantation and would avoid the chronic use of immunosuppressive agents. Successful transplantation of hematopoietic cells induces robust specific tolerance to donor antigens in allogeneic and xenogeneic models. The beta1 integrin class of adhesion molecules and their interactions with extracellular matrix components are thought to be integral to the engraftment and maturation of hematopoietic stem cells. We therefore examined the efficacy of porcine very late antigen-5 (VLA-5) and VLA-4 interactions with the human extracellular matrix (ECM) protein, fibronectin. Peripheral blood mononuclear cells (PBMCs) from humans and miniature swine were flourochrome labeled and adhesion to plates coated with whole human fibronectin (whFN) or its 120 KDa fragment containing the VLA-5 binding region was determined. Flow cytometry and immuno- precipitation were used to identify a monoclonal antibody that cross-reacted on porcine VLA-5. Human and pig PBMC adhesion to human fibronectin (hFN) or 120 kDa fragment-coated plates was assessed following incubation with control ab, anti-VLA-4, anti-VLA-5, or soluble fibronectin. Using rabbit complement, cells expressing VLA-5 were purged from PBMC preparations before performing the adhesion assay. Porcine and human PBMC both adhered to hFN in a divalent cation-dependent and activation-dependent manner. Adhesion to hFN of human but not pig PBMC was blocked by anti-VLA-5 monoclonal antibody SAM-1, although this mAb immunoprecipitated a heterodimeric cell surface molecule (155/135 kDa) resembling VLA-5 from pig PBMC. Complement-mediated depletion of VLA-5-expressing cells ablated specific binding of human but not porcine cells to hFN and its 120 kDa fragment. Addition of soluble fibronectin was capable of blocking adhesion of PBMC of both species to hFN. Anti-VLA-4 reduced the binding of PBMC from both species to hFN to a similar extent. Human and pig cells can specifically adhere to hFN and its 120 kDa fragment, suggesting that this critical cell-ECM interaction is preserved across species. While human cells exclusively use VLA-5 for binding to the 120 kDa fragment, porcine cells could not be shown to adhere to whFN or its 120 kDa fragment via VLA-5. However, porcine VLA-4 is capable of mediating adhesion to human FN. We conclude that disparities in the adhesive interactions of beta1 integrins may be a barrier to the use of porcine hematopoietic stem cell transplantation as a means of inducing donor-specific tolerance in the pig to human species combination.

Animals↗

PubMed2002

Biological therapy in transplantation: an update from the 19th International Congress of the Transplantation Society.

With the recent upsurge in pharmaceutical drugs changing the 'playing field' of transplantation therapeutics, the role of old agents, such as polyclonal antilymphocyte globulins and anti-CD3 monoclonal antibodies, is being revisited, with suggestions of using different, lower dose regimens to spare the use of other drugs. Similar suggestions have been made for the newer recombinant anti-CD25 antibodies. Numerous experimental models and a few early clinical models are evolving to try to determine the place of a range of biological reagents with specificities for novel targets. These include the costimulatory ligand-receptor pairs, such as CD40-CD154 and CD80/CD86-CD28, CD52 and CD45. The role of these newer agents is far from clear, but some of these early studies are very promising.

Animals↗

PubMedDate not supplied

Calcific uremic arteriolopathy presenting with small and large bowel involvement.

Calcific uremic arteriolopathy (CUA) is a rare complication of end-stage renal disease in which thrombosis occurs in calcified arteries, leading to infarction and infection of the affected tissues. This brief report describes a fatal case of CUA which presented with intestinal involvement, significantly before the onset of classical skin lesions. It is essential to raise awareness of this rare but clinically relevant form of presentation of CUA. The diagnostic and treatment issues are discussed in this case.

Adult↗