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Biomedical subjects

R I Lechler

Publications and source records attributed to R I Lechler.

At least 37 records · Page 2Linked to original sources
PubMed2001

The role of the allograft in the induction of donor-specific T cell hyporesponsiveness.

BACKGROUND: With adequate immunosuppression the majority of renal allografts are accepted, despite the exceptional vigour of the T cell alloimmune response. Previous work from this laboratory has demonstrated that this is accompanied by significant reductions in the precursor frequencies of anti-donor T cells. We have also shown that parenchymal cells are tolerogenic in vitro. We propose that the reduction in T cell frequencies may be due to the interaction between circulating T cells and potentially tolerogenic graft parenchymal cells. Primed/memory T cells (CD45RO+) are the only subset capable of reaching the allograft and therefore we would predict that T cell hyporesponsiveness would develop predominantly in the CD45RO+ subset due to their trafficking properties. METHODS: Frequencies of IL-2 secreting CD45RA+ and CD45RO+ CD4+ T cells in response to donor and third party stimulator cells were estimated in a series of renal transplant recipients, both before and after transplantation. RESULTS: There were highly significant reductions in the frequencies of donor-specific CD4+CD45RO+ T cells, when adjusted to control for the generalised effects of immunosuppression. There were no significant alterations in the frequencies of donor-specific CD4+CD45RA+ T cells. CONCLUSIONS: In renal transplant recipients, donor-specific CD4+ T cell hyporesponsiveness occurs predominantly in CD4+ CD45RO+ T cells which is the subset capable of trafficking through the graft.

Humans↗
PubMed2001

Requirement for leptin in the induction and progression of autoimmune encephalomyelitis.

Recent evidence indicates that leptin modifies T cell immunity, and may provide a key link between nutritional deficiency and immune dysfunction. To study the influence of leptin on autoimmunity, susceptibility to experimental autoimmune encephalomyelitis induced by immunization with a myelin-derived peptide was examined in leptin-deficient, C57BL/6J-ob/ob mice, with or without leptin replacement, and in wild-type controls. Leptin replacement converted disease resistance to susceptibility in the C57BL/6J-ob/ob mice; this was accompanied by a switch from a Th2 to Th1 pattern of cytokine release and consequent reversal of Ig subclass production. Our findings suggest that leptin is required for the induction and maintenance of an effective proinflammatory immune response in the CNS.

Adoptive Transfer↗
PubMed2001

Nitric oxide-mediated expression of Bcl-2 and Bcl-xl and protection from tumor necrosis factor-alpha-mediated apoptosis in porcine endothelial cells after exposure to low concentrations of xenoreactive natural antibody.

BACKGROUND: Cardiac and renal allo- and xenografts can acquire a natural resistance to vascular rejection. This "accommodation" involves endothelial cell (EC) expression of "survival genes" such as Bcl family members and hemoxygenase 1. Understanding what initiates this protective process would have profound implications; our hypothesis is that low concentrations of antigraft antibodies may mediate these changes. METHODS: In vitro cultured primary and immortalized porcine EC were incubated with polyclonal human IgG for 6 days and then examined for phenotype changes. RESULTS: The cells acquired resistance to tumor necrosis factor-alpha-mediated apoptosis (50-100% reduction at 6 hr) and up-regulated expression of Bcl-2 and Bcl-xl; sustained expression was accompanied by inducible nitric oxide (NO) synthase expression and by enhanced production of NO by EC. Two observations suggested that NO was actively involved in the process of Bcl-2 and Bcl-xl induction. First, (z)-1-2-[2-aminoethyl)-N- (2-ammonioethyl)amino]diazen-1-ium-1,2-diolate, an NO donor, was able to induce similar changes in porcine EC to those induced by anti-pig antibodies. Second, an NO synthase inhibitor NG-monomethyl-L-arginine.monoacetate was able to specifically inhibit the anti-pig antibody-mediated expression of Bcl-2 or Bcl-xl. CONCLUSIONS: These data strongly support the hypothesis that Bcl-2 and Bcl-xl expression and protection from apoptosis in EC may result from antibody-mediated NO production through the neoexpression of inducible NO synthase.

Animals↗
PubMed2001

Transferrin receptor-mediated gene transfer to the corneal endothelium.

BACKGROUND: The application of gene therapy to prevent allograft rejection requires the development of noninflammatory vectors. We have therefore investigated the use of a nonviral system, transferrin-mediated lipofection, to transfer genes into the cornea with the aim of preventing corneal graft rejection. METHODS: Rabbit and human corneas were cultured ex vivo and transfected with either lipofection alone or in conjunction with transferrin. The efficiency of transfection, localization, and kinetics of marker gene expression were determined. Strategies to increase gene expression, using chloroquine and EDTA, were investigated. In addition to a marker gene, a gene construct encoding viral interleukin 10 (vIL-10) was transfected and its functional effects were examined in vitro. RESULTS: Transferrin, liposome, and DNA were demonstrated to interact with each other, forming a complex. This complex was found to deliver genes selectively to the endothelium of corneas resulting in gene expression. Treatment of corneas with chloroquine and EDTA increased the transfection efficiency eight-fold and threefold, respectively. We also demonstrated that constructs encoding vIL-10 could be delivered to the endothelium. Secreted vIL-10 was shown to be functionally active by inhibition of a mixed lymphocyte reaction. CONCLUSIONS: Our data indicate that transferrin-mediated lipofection is a comparatively efficient nonviral method for delivering genes to the corneal endothelium. Its potential for use in preventing graft rejection is shown by the ability of this system to induce vIL-10 expression at secreted levels high enough to be functional.

Animals↗
PubMed2001

Leptin potentiates experimental autoimmune encephalomyelitis in SJL female mice and confers susceptibility to males.

SJL (H-2s) female mice are more susceptible than males to experimental autoimmune encephalomyelitis (EAE) induced by immunization with myelin-derived peptides. The reasons for this sexual dimorphism are unclear, but may include such factors as sex-related differences in immune responsiveness, hormonal effects and sex-linked genetic factors. Recent evidence indicates that leptin modifies T cell immunity promoting T helper (Th) 1 pro-inflammatory immune responses. Circulating leptin levels show a marked sexual dimorphism, being higher in females than in males. In the present study, we investigated whether leptin treatment altered the course of relapsing-remitting EAE, induced by the proteolipid protein peptide (PLP(139-151)), in SJL susceptible females and EAE-resistant males. Administration of leptin to female SJL mice before or after disease onset significantly worsened the disease, with a concomitant increase in the PLP(139-151)-specific delayed-type hypersensitivity (DTH) reactivity and in vitro IFN-gamma secretion. Leptin treatment at priming with antigen or before disease onset rendered male SJL mice susceptible to EAE, with the appearance of PLP(139-151)-specific DTH reactivity and a switch from a Th2 to Th1 pattern of cytokine release. Our findings indicate that leptin administration to susceptible females resulted in a more severe disease, and that reduced leptin levels in male SJL mice may contribute to the gender-related differences in the induction phase of EAE.

Amino Acid Sequence↗
PubMed2001

Allorecognition.

Until recently, the vigorous T cell response via the direct pathway has overshadowed studies involving the indirect pathway. Thus, while the direct pathway has previously been considered to be the main driving force in alloimmune responses, there is an increasing body of data to support a prominent role of the indirect pathway in transplant rejection. Most importantly, while the direct anti-donor alloresponse diminishes with time after transplantation, the indirect alloresponse is likely to be permanently active due to traffic of recipient dendritic cells (DCs) through the graft. Consequently, the future challenge in the induction of allograft tolerance is to design interventions that will target the cells involved in the indirect pathway, especially the T cells with indirect allospecificity.

Animals↗
PubMed2001

Human thrombin and FXa mediate porcine endothelial cell activation; modulation by expression of TFPI-CD4 and hirudin-CD4 fusion proteins.

Aside from their critical role in thrombosis, activated coagulation factors also have inflammatory properties and these may be important during delayed xenograft rejection (DXR). This study assessed whether porcine EC could be activated by factor Xa (FXa) and thrombin (FIIa) and whether expression of tissue factor pathway inhibitor (TFPI)-CD4 and hirudin-CD4 fusion proteins could prevent such activation. Incubation of porcine EC with human FXa and FIIa induced cell surface expression of E-selectin, VCAM and tissue factor (TF) in a time-dependent and concentration-dependent manner. In contrast, porcine EC transfected with a human TFPI-CD4 fusion protein were selectively resistant to these pro-inflammatory effects of FXa but not FIIa. Likewise, the transfectants expressing the hirudin-CD4 fusion protein were selectively resistant to the pro-inflammatory effects of FIIa but not those of FXa. When combined, the FXa and FIIa had an additive effect on the activation of control EC. In contrast, coexpression of both hirudin-CD4 and TFPI-CD4 fusion proteins completely inhibited the upregulation of VCAM with the FXa/FIIa mix. These results indicate that expression of novel anticoagulant fusion proteins on the surface of porcine EC can protect against EC activation induced by human coagulation factors FXa and FIIa. In vivo, we anticipate that expression of these fusion proteins on the endothelium of transplanted xenografts, besides preventing intravascular thrombosis, will also protect against EC activation induced by trace amounts of FIIa and FXa, thereby further protecting the grafts from DXR.

Animals↗
PubMed2001

Transplant accommodation in highly sensitized patients: a potential role for Bcl-xL and alloantibody.

Transplantation of renal allografts into recipients with circulating anti-HLA antibodies results in hyperacute rejection. In some cases, however, antibodies return without causing harm; this phenomenon has been termed 'accommodation'. We have investigated this process in human allotransplantation. We removed anti-HLA antibodies by immunoadsorption in seven highly sensitized dialysis patients who subsequently underwent renal transplantation. Immunohistochemistry of renal biopsies for IgG and antiapoptotic proteins was performed. We also developed a model of 'accommodation' using anti-HLA antibodies eluted from sensitized patients and incubated with human umbilical vein endothelial cells (HUVECs) at different concentrations. Their effect on HUVEC phenotype was then analysed. Anti-donor antibody returned in 4/7 patients, without evidence of hyperacute rejection. Three out of four of these 'accommodated' grafts showed specific endothelial up-regulation of Bcl-xL and 2/2 tested positive for endothelial IgG deposition. HUVECs incubated with subsaturating concentrations of anti-HLA antibody showed increased expression of Bcl-xL, were rendered refractory to endothelial cell activation and became resistant to complement-mediated lysis. In contrast, HUVECs incubated with saturating concentrations underwent activation and expressed low levels of Bcl-xL. In conclusion, endothelial Bcl-xL expression defines the accommodation process in human allografts and this phenotype may be initiated by exposure of endothelium to low concentrations of anti-donor HLA antibodies.

Adult↗
PubMed2001

Allorecognition.

Until recently, the vigorous T-cell response via the direct pathway has overshadowed studies involving the indirect pathway. Thus, while the direct pathway has previously been considered to be the main driving force in alloimmune responses, there is an increasing body of data to support a prominent role of the indirect pathway in transplant rejection. Most importantly, the direct antidonor alloresponse diminishes with time after transplantation, possibly due to the tolerogenic effects of alloantigen presentation by the parenchymal cells of the transplant. In contrast, the indirect alloresponse is likely to be permanently active, due to traffic of recipient dendritic cells (DCs) through the graft. The challenge that this poses in the pursuit of clinical transplant tolerance is how to induce tolerance in T cells with indirect allospecificity.

Graft Rejection↗
PubMed2000

Isolation of endothelial cells from murine tissue.

The isolation and long-term culture of murine endothelial cells (ECs) has often proven a difficult task. In this paper we describe a quick, efficient protocol for the isolation of microvascular endothelial cells from murine tissues. Murine lung or heart are mechanically minced and enzymatically digested with collagenase and trypsin. The single cell suspension obtained is then incubated with an anti-CD31 antibody, anti-CD105 antibody and with biotinylated isolectin B-4. Pure EC populations are finally obtained by magnetic bead separation using rat anti-mouse Ig- and streptavidin-conjugated microbeads. EC cultures are subsequently expanded and characterised. The surface molecule expression by the primary cultures of murine EC obtained from lung and heart tissue is analysed and compared to that of a murine endothelioma and of primary cultures of murine renal tubular epithelial cells. The phenotype and morphology of these cultures remain stable over 10-15 passages in culture, and no overgrowth of contaminating cells of non-endothelial origin is observed at any stage.

Animals↗
PubMed2000

Activated murine endothelial cells have reduced immunogenicity for CD8+ T cells: a mechanism of immunoregulation?

The immunogenic properties of primary cultures of murine lung microvascular endothelial cells (EC) were analyzed. Resting endothelial cells were found to constitutively express low levels of MHC class I and CD80 molecules. IFN-gamma treatment of EC resulted in a marked up-regulation of MHC class I, but no change was observed in the level of CD80 expression. No CD86 molecules were detectable under either condition. The ability of peptide-pulsed EC to induce the proliferation of either the HY-specific, H2-K(k)-restricted CD8(+) T cell clone (C6) or C6 TCR-transgenic naive CD8(+) T cells was analyzed. Resting T cells were stimulated to divide by quiescent peptide-prepulsed EC, while peptide-pulsed, cytokine-activated EC lost the ability to induce T cell division. Furthermore, Ag presentation by cytokine-activated EC induced CD8(+) T cell hyporesponsiveness. The immunogenicity of activated EC could be restored by adding nonsaturating concentrations of anti-H2-K(k) Ab in the presence of an optimal concentration of cognate peptide. This is consistent with the suggestion that the ratio of TCR engagement to costimulation determines the outcome of T cell recognition. In contrast, activated peptide-pulsed EC were killed more efficiently by fully differentiated effector CD8(+) T cells. Finally, evidence is provided that Ag recognition of EC can profoundly affect the transendothelial migration of CD8(+) T cells. Taken together, these results suggest that EC immunogenicity is regulated in a manner that contributes to peripheral tolerance.

Animals↗
PubMed2000

Porcine CTLA4-Ig lacks a MYPPPY motif, binds inefficiently to human B7 and specifically suppresses human CD4+ T cell responses costimulated by pig but not human B7.

The CTLA4 receptor (CD152) on activated T lymphocytes binds B7 molecules (CD80 and CD86) on APC and delivers a signal that inhibits T cell proliferation. Several regions involved in binding to B7 are known, but the relative importance of these is not clear. We have cloned porcine CTLA4 (pCTLA4). Although highly homologous to human CTLA4 (hCTLA4), the predicted protein sequence contains a leucine for methionine substitution at position 97 in the MYPPPY sequence. A fusion protein constructed from the extracellular regions of pCTLA4 and the constant regions of human IgG1 (pCTLA4-Ig) bound porcine CD86 with equivalent affinity to that of hCTLA4-Ig. However, pCTLA4-Ig bound poorly to human CD80 and CD86 expressed on transfectants and EBV-transformed human B cells. In functional assays with MHC class II-expressing porcine endothelial cells and human B cells, pCTLA4-Ig blocked human CD4+ T cell responses to pig but not human cells, whereas control hCTLA4-Ig inhibited responses to both. Comparison between mouse, human, and porcine CTLA4-Ig suggests that the selective binding of pCTLA4-Ig to porcine CD86 molecules is due to the L for M substitution at position 97. Our results indicate that pCTLA4-Ig may be a useful reagent to define the precise nature of the interaction between B7 and CTLA4. By failing to inhibit the delivery of costimulatory signals provided by human B7, it may also prove to be a relatively specific inhibitor of the direct human T cell response to immunogenic pig tissue.

Abatacept↗
PubMed2000

Cloning of porcine intercellular adhesion molecule-1 and characterization of its induction on endothelial cells by cytokines.

BACKGROUND: The transplantation of pig organs into humans requires a detailed knowledge of similarities and differences between the two species in the molecular physiology of host defense mechanisms. We therefore set out to identify porcine intercellular adhesion molecule (ICAM)-1 and to characterize its expression by endothelial cells. METHODS: Porcine ICAM-1 cDNA was isolated from an endothelial cell cDNA library. An anti-pig ICAM-1 monoclonal antibody was generated and used to investigate the regulation by cytokines of ICAM-1 expression by porcine aortic endothelial cells (PAEC), using flow cytometry. RESULTS: We found that porcine ICAM-1 was similar in primary structure to human ICAM-1, with five Ig-like domains. COS-7 cells transfected with porcine ICAM-1 supported beta2 but not alpha4 integrin-dependent adhesion of human T lymphoblasts. There was a low-level surface expression of ICAM-1 on unstimulated PAEC and increased expression after stimulation with tumor necrosis factor (TNF)-alpha. However expression of ICAM-1 seemed to be significantly lower than that of vascular cell adhesion molecule-1, both on unstimulated and TNF-alpha-activated PAEC. Recombinant porcine interferon-gamma weakly stimulated ICAM-1 expression when incubated alone with PAEC but had an inhibitory effect on the increase in ICAM-1 due to TNF-alpha, both at 8 and 24 hr. CONCLUSIONS: Our observations confirm the existence of ICAM-1 in the pig and provide novel insights into how porcine and human endothelial cells differ in terms of adhesion molecule expression and cytokine responsiveness. Such differences are potentially important in interpreting models of inflammation in the pig and also in understanding the process of rejection of porcine xenografts.

Amino Acid Sequence↗
PubMed2000

Peptide analogues as a strategy to induce tolerance in T cells with indirect allospecificity.

BACKGROUND: It has been demonstrated that indirect recognition of allogeneic MHC molecules might play an important role in provoking graft rejection. Although direct recognition of allogeneic molecules on antigen presenting cells of the graft may induce a state of tolerance, the continuous presentation of processed alloantigens by specialized antigen presenting cells does not allow the same phenomenon to occur. Tolerance to interleukin-2 secreting T cells can be achieved in different ways, among these is the exposure to mutants of the wild type allopeptide. We have investigated whether peptide analogues of the allopeptide can induce tolerance in T cells with indirect allospecificity. METHODS: T cell clones with indirect anti-HLA-A2-specificity generated from a HLA-A2-DRB1*1502+ patient who chronically rejected a HLA-A2-expressing kidney allograft were used for this study. Nine peptide analogues of HLA-A2 (residues: 103-120) were produced with single amino acid substitutions at the putative T cell receptor for antigen contact positions. Their effect on the proliferation of a panel of T cell clones was evaluated. RESULTS: Peptide analogues and wild type peptide had similar capacity to bind to the restriction molecule HLA-DRB1*1502. Co-presentation of the peptide analogues 111R/A, H, K and 114H/K, with the wild type peptide inhibited T cell responses, indicative of antagonism. In addition, one analogue 112G/S induced unresponsiveness in the T cells to subsequent culture with the wild type peptide. CONCLUSIONS: The data presented here suggest that using reagents such as altered peptides may represent a strategy to prevent the activation of T cells with indirect alloreactivity and allograft rejection in vivo.

Amino Acid Sequence↗
PubMed2000

Significant frequencies of T cells with indirect anti-donor specificity in heart graft recipients with chronic rejection.

BACKGROUND: The purpose of this study was to determine whether T cells with indirect allospecificity could be detected in heart transplant recipients with chronic rejection. METHOD AND RESULTS: Human T-cell clones were used to determine the most effective way to deliver major histocompatibility complex alloantigens for indirect presentation. Seven allograft recipients with evidence of progressive, chronic rejection were selected. Four heart graft recipients with no evidence of chronic rejection were used as controls. Peripheral blood T cells and antigen-presenting cells from the recipients were cultured with frozen/thawed stored donor cells or major histocompatibility complex class I-derived synthetic peptides in limiting dilution cultures and then compared with controls using tetanus toxoid and frozen/thawed third-party cells with no human leukocyte antigens in common with the donor. In 5 of 7 patients analyzed who had chronic rejection, elevated frequencies of T cells with indirect, anti-donor specificity (iHTLf) were detected. No such elevated iHTLf were detected in recipients without chronic rejection. DISCUSSION: iHTLf can be obtained from human transplant recipients, which supports the contention that the indirect pathway is involved in chronic transplant rejection.

Animals↗
PubMed2000

HLA-G inhibits the transendothelial migration of human NK cells.

The expression of the non-classical MHC class I molecule HLA-G is normally restricted to the placenta during pregnancy, where it is found on fetal endothelial cells and on invasive cytotrophoblast cells, specifically those at the maternal / fetal interface. Its precise physiological role has yet to be defined. HLA-G may have nonimmune functions relating to angiogenesis and placentation, but most evidence suggests that it protects fetal cells from lysis by maternal uterine NK cells, which are found in large numbers around invading trophoblast cells. This effect is due to specific interaction with inhibitory receptors expressed on NK cells. We have examined the hypothesis that another function of HLA-G is to inhibit NK cell migration. Using an in vitro transmigration assay system, we present data to support this hypothesis. NK cell migration across porcine endothelial cells transfected with HLA-G1 was specifically inhibited compared to migration across HLA-A2-transfected monolayers. HLA- G1 had no influence on the migration of a control T lymphocyte line. These results support the idea that in vivo, HLA-G may inhibit NK cell traffic across the placenta.

Cell Movement↗