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M H Sayegh

Publications and source records attributed to M H Sayegh.

At least 145 records · Page 8Linked to original sources
PubMed1995

Blocking cell microtubule assembly inhibits the alloimmune response in vitro and prolongs renal allograft survival by inhibition of Th1 and sparing of Th2 cell function in vivo.

Colchicine inhibits cell microtubule assembly by binding to and preventing the polymerization of tubulin monomers. Although there are data to indicate that colchicine inhibits a variety of cell-mediated immune responses, the effects and mechanisms of inhibiting cell microtubule assembly on the alloimmune response have not been thoroughly investigated. It has recently been shown that colchicine prevents acute rejection and promotes the long-term survival of rat renal allografts. In this study, the effects and mechanisms of inhibiting cell microtubule assembly by colchicine on the alloimmune response in vitro and in vivo were examined. First, the effects of colchicine on T lymphocyte response to alloantigen in vitro were tested. In the standard one-way mixed lymphocyte response (MLR), responder Lewis rat lymph node cells were cultured with irradiated Brown-Norway stimulators. Colchicine inhibited the MLR in a dose-dependent manner, with 100% inhibition at a concentration of 25 ng/mL (6.25 x 10(-8) M) and 50% inhibition at a concentration of approximately 5 to 10 ng/mL. Colchicine also inhibited the generation of cytotoxic T lymphocytes as well as cytotoxic T cell effector function in vitro in a dose-dependent fashion. Second, detailed immunohistologic studies of renal allografts harvested from unmodified control (acutely rejecting) and colchicine-treated rats (Day 15 or 30) were performed. These studies showed that grafts from colchicine-treated animals had significantly fewer mononuclear cell infiltrates and less edema, and moderately decreased deposition of immunoglobulin M, C3, and fibrin, as compared with acutely rejecting control grafts.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

The thymic way to transplantation tolerance.

Within the past three decades, extensive research has been carried out with the aim to prevent graft rejection by minimizing the side effects related to the use of immunosuppressants. The major goal in transplantation research remains the development of strategies that would allow one to achieve a state of donor-specific unresponsiveness in order to promote a condition of true tolerance without the need of immunosuppressants. Recent evidence has been provided that this is a pursuing goal, at least in experimental animals. The thymus plays the major role in the development of self-tolerance, and initial work in the late 1960s indicated that the thymus also plays a critical role in the induction of acquired tolerance to exogenous antigens. Recently, the interest in acquired thymic tolerance has been renewed by the observation that, in the rat, the thymus is an immunologically privileged site in which isolated pancreatic islets can be engrafted and survive indefinitely. Moreover, intrathymic injection of the islets induced donor-specific unresponsiveness, which allowed survival of a second donor-strain islet cell allograft transplanted into an extrathymic site. These findings on cellular allografts have been extended to vascularized organ allografts.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

T cell costimulatory pathways: promising novel targets for immunosuppression and tolerance induction.

It is now accepted that T cells need two signals for full activation. The first is the foreign antigen itself presented by self-major histocompatibility complex and thus provides antigen specificity to the immune response. The second is a "costimulatory" signal, the best-characterized of which is provided through the T cell accessory molecule CD28. In vitro, the blockade of costimulatory signals inhibits T cell activation and induces a state of antigen-specific unresponsiveness. In vivo, agents that block CD28-mediated costimulation have proved extremely effective in inhibiting the immune response in experimental models of transplantation and autoimmune disease, providing novel strategies for use in clinical trials in the near future.

Animals↗
PubMed1995

Up-regulation of endothelin-1 mRNA and peptide expression in rat cardiac allografts with rejection and arteriosclerosis.

Acute and chronic rejection are frequent and significant complications of cardiac transplantation, and graft arteriosclerosis is the leading cause of death beyond the first year after transplant. Levels of endothelin-1 (ET-1) are elevated in plasma of patients with cardiac allografts and those with symptomatic vascular atherosclerosis, but little is known about the role of ET-1 in these processes. This study examined intragraft ET-1 expression in rat cardiac models of acute rejection and chronic rejection associated with graft arteriosclerosis. Corrected ET-1 gene transcript levels were measured with a [32P]dCTP reverse transcription polymerase chain reaction assay normalized with glyceraldehyde-3-phosphate dehydrogenase, and the gene product was evaluated by immunohistology with a monospecific anti-ET-1 antibody at different time points after transplant. ET-1 mRNA levels were significantly increased in acutely rejected (Wistar-Furth rat cardiac allografts transplanted into Lewis rat recipients) and chronically rejected (Lewis allografts transplanted into F344 recipients) vascularized cardiac allografts as compared with isograft controls. In acutely rejected allografts, peak expression occurred on day 5 after transplant. In chronically rejected allografts, the increase in ET-1 mRNA was sustained on days 7, 28, and 75. In both acutely and chronically rejected allografts, ET-1 mRNA upregulation was not seen in host spleens or paired host hearts. Immunohistological analysis confirmed that the bulk of ET-1 peptide expression was localized to mononuclear cells that diffusely infiltrated the graft interstitium (acute rejection and early chronic rejection) and accumulated within the neointima of chronically rejecting hearts with arteriosclerosis. These observations, taken together with in vitro data showing that ET-1 production is stimulated by certain cytokines, indicate that the allogeneic stimulus within rejecting vascularized cardiac allografts, presumably cytokine mediated, leads to significant intragraft up-regulation of ET-1 mRNA and peptide expression. The local up-regulation of this vasoactive and mitogenic peptide within acutely and chronically rejected cardiac allografts suggests that ET-1 may be involved in the development of graft arteriosclerosis.

Animals↗
PubMed1994

Thromboxane A2 receptor blocking abrogates donor-specific unresponsiveness to renal allografts induced by thymic recognition of major histocompatibility allopeptides.

Recent in vitro studies have documented that thromboxane (Tx)A2 induces thymocyte apoptosis by acting on specific receptors abundantly expressed on the surface of immature T lymphocytes. No information is available on the in vivo relevance of this observation in development of self- or acquired tolerance. We and others have previously documented that injection of donor cells into adult thymus of experimental animals induced specific systemic unresponsiveness to allografts in the rat and mouse models. More recently, we have shown that intrathymic injection of synthetic class II major histocompatibility complex (MHC) allopeptides resulted in donor-specific unresponsiveness to renal allografts. The induction of unresponsiveness was abrogated by recipient thymectomy within the first week. We now report the effect of TxA2 blockade on acquired thymic tolerance to renal allografts induced by intrathymic injection of synthetic class II MHC allopeptides in the Wistar-Furth (WF) to Lewis rat strain combination. Administration of the TxA2 receptor blocker prior to transplantation or 2 wk postengraftment completely abrogated the unresponsive state. In addition, inhibiting the TxA2-forming enzyme by aspirin or dexamethasone also abolished the induction of acquired thymic tolerance. Evidence is also provided for a critical "dose" of peptides to be injected into the thymus to induce systemic unresponsiveness to renal allografts. These data, coupled with observations that activated peripheral T cells can circulate through the thymus, provide evidence that TxA2/TxA2 receptor interaction in the thymic microenvironment, leading to anergy/programmed cell death of activated T cells, may play an important role in the development of acquired unresponsiveness in vivo.

Animals↗
PubMed1994

Mechanisms of acquired thymic unresponsiveness to renal allografts. Thymic recognition of immunodominant allo-MHC peptides induces peripheral T cell anergy.

We have recently shown that a single intrathymic injection of synthetic 25mer peptides, representing full sequences of the hypervariable domain of RT1.BuB (4 peptides) and RT1.Du beta (4 peptides) WF class II MHC molecules, 48 hr before transplantation induces donor-specific unresponsiveness to WF rat renal allografts in adult LEW recipients. The induction of unresponsiveness was abrogated by the recipient's thymectomy within the first week after intrathymic injection. Peripheral T cells of long-term survivors exhibited antigen-specific hyporesponsiveness in the LEW x WF MLR. Studies on the mechanisms of induction of acquired thymic unresponsiveness to alloantigen in vivo and in vitro are now reported. First, since we have previously demonstrated in LEW responders that only 4 of the 8 synthetic 25mer peptides, 2 RT1.Du beta and 2 RT1.Bu beta sequences, were immunogenic in vitro and in vivo, we compared the tolerogenicity of the immunogenic versus the nonimmunogenic peptides. While LEW rats intrathymically injected with the nonimmunogenic peptides acutely rejected their renal allografts within 6-10 days, animals injected with the immunogenic peptides did not reject their grafts and are surviving > 100 days with normal allograft function. In vitro studies established that peripheral T cells from intrathymically tolerized animals exhibited antigen-specific hyporesponsiveness in the LEW x WF MLR starting as early as 1 week posttransplant. Immunohistological evaluation of renal allografts from intrathymically tolerized animals 1 week postengraftment showed marked reduction in mononuclear cell infiltrates with no evidence of tubulitis, and marked reduction in intragraft staining for activation and inflammatory cytokines and alloantibodies, as compared with acutely rejecting controls. Systemic administration of 1000 U of rIL-2 daily for 5 days starting on the day of transplantation abrogated the tolerogenic effect of intrathymic MHC allopeptides. Injection of 100 micrograms of a single immunogenic peptide, RT1.Du beta 2 (residues 20-44), into the thymus of responder LEW rats 48 hrs before immunization with RT1.Du beta 2 effected significant reduction of in vitro proliferation of primed lymphocytes to RT1.Du beta 2, an effect that was abrogated by addition of rIL-2 in vitro. In contrast, thymectomy beyond 2 weeks and administration of rIL-2 at 4-6 weeks after transplantation failed to cause rejection. These observations indicate that thymic recognition of immunodominant class II MHC allopeptides leads to peripheral T cell anergy that mediates the induction phase of systemic unresponsiveness to renal allografts. The maintenance phase appears to be mediated by dense anergy or clonal deletion.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Intrathymic injection of donor-specific X-irradiation-sensitive spleen cells abrogates accelerated rejection of cardiac allografts in sensitized rats.

LBNF1 cardiac allografts are rejected within 36 hr in Lewis (LEW) rats sensitized with Brown Norway (BN) skin grafts (acute rejection = 7.5 days). We analyzed the effects of intrathymic versus intravenous alloantigen challenge upon graft survival in this well-defined accelerated rejection model. Intrathymic injection of LBNF1 spleen cells (2 x 10(7)) at the time of skin transplantation (day -7) abrogated < 36 hr rejection, and prolonged the survival of cardiac allografts to about 11 days. This striking effect did not require concomitant immunosuppression, and was donor specific, as the transfer of syngeneic (LEW) or third-party (Wistar-Furth) splenocytes was ineffective. X-irradiation of donor spleen cells before inoculation restored accelerated rejection, whereas thymectomy at day -6 or 0 (the day of heart transplant) significantly shortened graft survival. In contrast, although intravenous administration of the same number of donor cells into sensitized recipients prolonged cardiac allograft survival to about 9 days, the effect was x-irradiation resistant and was never influenced by thymectomy. Radioactive tracer studies have revealed distinct trafficking patterns for the transferred cells, with those given intrathymically retained mostly in the thymus, and sequestered into host spleen and lymph nodes. Instead, intravenously injected splenocytes did not accumulate in the thymus, but were eventually trapped in the liver. Moreover, intrathymic immunomodulation has switched off cellular, rather than humoral, events at the graft site, and markedly depressed cell proliferative responses in host lymphoid organs, as analyzed by immunohistology and mixed lymphocyte response (MLR)* assay, respectively. In contrast, intravenous therapy did not have any significant effect on early intragraft cellular infiltration, including considerable neutrophil infiltration, and did not affect lymph node cell proliferation in vitro. These data document the importance of the thymus as a potential target organ for modulation of alloreactivity in vivo, and reinforce the role of distinct "central" and "peripheral" host immune mechanisms contributing to immunological unresponsiveness following organ transplantation.

Animals↗
PubMed1994

Mechanisms of allo-recognition. Recognition by in vivo-primed T cells of specific major histocompatibility complex polymorphisms presented as peptides by responder antigen-presenting cells.

There is evidence of two pathways of allorecognition, the direct pathway where T cells recognize intact allo-MHC molecules on the surface of target cells, and the indirect pathway where T cells recognize processed allo-MHC presented by self antigen-presenting cells. We used synthetic class II MHC allopeptides to study the cellular mechanisms of the indirect allorecognition pathway and its potential role in vascularized allograft rejection. LEW (RT1l) rat T cells--which are primed by immunization with a mixture of four 25 mer class II MHC allopeptides, representing the full length sequence of the beta chain of the hypervariable domain of the RT1.Du (WF), or by primary WF (RT1u) vascularized cardiac allografts--were capable of recognizing and proliferating to specific polymorphic class II MHC sequences when presented as peptides by responder APCs. T cells from naive LEW animals, WF animals immunized with syngeneic RT1.Du beta peptides, or LEW recipients of third-party BN (RT1n) vascularized cardiac allografts did not proliferate to the RT1.Du beta peptides, indicating the specificity of allopeptide recognition. In the strain combination used, immunogenicity of class II MHC allopeptides is determined by factors other than polymorphisms alone, since epitopic differences in 2 of the 4 RT1.Du beta allopeptides were not immunogenic. Responder T cells were CD4+, and were inhibited by monomorphic anticlass II monoclonal antibodies, and by specific anticlass II alloantibodies. These observations confirm the occurrence of self MHC-restricted recognition of processed allo-MHC in primary vascularized allograft rejection, and provide the rationale to develop novel and specific immunotherapies in organ transplantation.

Animals↗
PubMed1994

Rat intestinal epithelial cells present major histocompatibility complex allopeptides to primed T cells.

BACKGROUND/AIMS: Intestinal epithelial cells present protein antigens to primed T cells in vitro. The aim of this study was to investigate whether intestinal epithelial cells present peptide antigens in vitro and in vivo after oral administration. METHODS: Small intestinal epithelial cells from naive LEW (RT1) rats pulsed in vitro with a synthetic immunogenic major histocompatibility complex allopeptide, RT1.Du beta 20-44, or in vivo by oral administration of the peptide were tested for their ability to induce specific proliferation of LEW T cells primed in vivo to RT1.Du beta 20-44. RESULTS: In vitro pulsed intestinal epithelial cells induced specific proliferation of RT1.Du beta 20-44-primed T cells. Intestinal epithelial cells isolated from LEW ras that received a single oral dose of RT1.Du beta 20-44 18 hours earlier also induced specific proliferation of RT1.Du beta 20-44-primed LEW T cells. Furthermore, epithelial cells harvested from LEW rats that received WF (RT1u) splenocytes orally 18 hours earlier induced specific proliferation of RT1.Du beta 20-44-primed LEW T cells. CONCLUSIONS: Intestinal epithelial cells take up processed alloantigen in vitro and in vivo for presentation as peptides to primed T cells. These observations provide a novel approach to study the role of the intestinal immune system in immune regulation in vivo.

Administration, Oral↗
PubMed1994

Late renal allograft failure secondary to thrombotic microangiopathy-human immunodeficiency virus nephropathy.

The case of a renal transplant recipient with a known history of iv drug abuse but unknown human immunodeficiency virus (HIV) status who presents after having a stable renal allograft function for 4 yr, with acute/subacute advanced renal failure, nephrotic syndrome, and hypertension, as well as clinical and histologic findings of thrombotic microangiopathy, is reported. He was subsequently found to have a positive serology for HIV-1 with a low CD4 count but no clinical manifestations of the acquired immunodeficiency syndrome. He was treated conservatively with zidovudine (AZT). The patient never regained graft function and was ultimately discharged from the hospital on maintenance dialytic therapy. This is, to our knowledge, the first report of thrombotic microangiopathy in an HIV-1-infected patient presenting late in the course as acute/subacute renal allograft failure.

AIDS-Associated Nephropathy↗
PubMed1994

CD4+ mononuclear cells induce cytokine expression, vascular smooth muscle cell proliferation, and arterial occlusion after endothelial injury.

Studies of T cell-deficient or immunosuppressed animals undergoing arterial endothelial denudation have yielded conflicting results as to the contribution of the immune system to neointimal vascular smooth muscle cell accumulation and proliferation. We investigated the cell types and cytokine expression associated with intimal hyperplasia occurring 14 days after balloon angioplasty of the carotid artery in Sprague-Dawley rats. Immunohistological studies using monoclonal antibodies showed that the carotid luminal occlusion observed was associated with smooth muscle cell proliferation and neointimal accumulation of large numbers of CD4+, ED1+ mononuclear cells but no T cells. There was also wide-spread staining for the inflammatory cytokine interleukin-1B (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), and IL-8, as well as dense expression of the potent smooth muscle mitogens platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-beta), and protein S. The relationship of smooth muscle cell proliferation to monocyte/macrophage accumulation and cytokine expression was tested by daily intraperitoneal administration for 14 days of a rat CD4-specific monoclonal antibody, BWH-4 (500 micrograms/day). Morphometric analysis at day 14 showed that the intimal area of animals treated with CD4 monoclonal antibody comprised 7% +/- 4% of the arterial wall compared with 50% +/- 6% in control animals (n = 6/group, P < 0.001). In addition, immunohistological studies showed that CD4 monoclonal antibody treatment markedly reduced the intimal accumulation of mononuclear and smooth muscle cells and essentially abrogated expression of the cytokines PDGF-BB, TGF-beta, IL-1 beta, TNF-alpha, and IL-8, plus the anticoagulant molecule, protein S. Our results document the extensive expression in vivo of cytokines that in vitro promote vascular smooth muscle cell proliferation, and suggest that CD4+ mononuclear cells or their secreted products play a key role in the pathogenesis of intimal hyperplasia after endothelial injury. Furthermore, these observations may have clinical relevance in the development of novel strategies to prevent arteriosclerosis.

Angioplasty, Balloon↗
PubMed1994

Chronic rejection in experimental cardiac transplantation in a rat model.

The most significant pathologic finding in chronically rejected organ grafts is diffuse concentric intimal proliferation in the arterial system. To develop a reproducible model of chronic vascular rejection in cardiac grafts which we could then use to study the pathogenesis and therapy of this disease process, we exchanged heterotopic cardiac allografts across minor histocompatibility barriers using commercially available Lewis rats as donors and F-344 rats as recipients. We found that all long-term surviving allografts developed diffuse graft arteriosclerotic lesions which were virtually identical in appearance to those seen in chronically rejected human cardiac grafts. Immunohistochemical studies confirm that end-stage lesions are similar in composition to human lesions and are made up predominantly of vascular smooth muscle cells with occasional monocytes and T cells. Analysis of continuous series of rejecting allografts demonstrates that a distinct inflammatory stage precedes smooth muscle cell accumulation in areas of intimal thickening, suggesting that mononuclear cells play a role in the developing lesion. Endothelial expression of class II and ICAM-1 probably underlies early mononuclear cell adherence to the endothelium. Analysis using quantitative RT-PCR and immunocytochemistry confirms MCP-1 is expressed by ED1-positive monocyte/macrophages in rejecting cardiac grafts, suggesting this chemoattractant may help drive mononuclear cell accumulation in the expanding intima. Immunohistochemical labelling of PDGF, TNF and IL-1 beta in vascular lesions suggests these factors may trigger intimal vascular smooth muscle cell proliferation in chronically rejecting allografts, as they, along with protein S, were closely associated with sites of intimal hyperplasia and smooth muscle cell proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗