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A Bushell

Publications and source records attributed to A Bushell.

At least 19 recordsLinked to original sources
PubMed2001

Critical role for IL-4 in the development of transplant arteriosclerosis in the absence of CD40-CD154 costimulation.

Blockade of the CD40-CD154 pathway can inhibit CD4(+) T cell activation but is unable to prevent immune responses mediated by CD8(+) T cells. However, even in the absence of CD8(+) T cells, inhibition of the CD40-CD154 pathway is insufficient to prevent the development of transplant arteriosclerosis. This study investigated the mechanisms of transplant arteriosclerosis in the absence of the CD40 pathway. C57BL/6 CD40(-/-) (H2(b)) recipients were transplanted with MHC-mismatched BALB/c (H2(d)) aortas. Transplant arteriosclerosis was evident in both CD40(-/-) and CD40(+/-) mice (intimal proliferation was 59 +/- 5% for CD40(-/-) mice vs 58 +/- 4% for CD40(+/-) mice) in the presence or absence of CD8(+) T cells (intimal proliferation was 46 +/- 7% for CD40(-/-) anti-CD8-treated mice vs 50 +/- 10% for CD40(+/-) anti-CD8-treated mice), confirming that CD8(+) T cells are not essential effector cells for the development of this disease. In CD40(-/-) recipients depleted of CD8(+) T cells, the number of eosinophils infiltrating the graft was markedly increased (109 +/- 24 eosinophils/grid for CD40(-/-) anti-CD8-treated mice vs 28 +/- 7 for CD40(+/-) anti-CD8-treated mice). The increased presence of eosinophils correlated with augmented intragraft production of IL-4. To test the hypothesis that IL-4 was responsible for the intimal proliferation, CD8 T cell-depleted CD40(-/-) recipients were treated with anti-IL-4 mAb. This resulted in significantly reduced eosinophil infiltration into the graft (12 +/- 5 eosinophils/grid for CD40(-/-) anti-CD8(+), anti-IL-4-treated mice vs 109 +/- 24 for CD40(-/-) anti-CD8-treated mice), intragraft eotaxin, CCR3 mRNA production, and the level of intimal proliferation (18 +/- 5% for CD40(-/-) anti-CD8(+)-, anti-IL-4-treated mice vs 46 +/- 7% for CD40(-/-) anti-CD8-treated mice). In conclusion, elevated intragraft IL-4 production results in an eosinophil infiltrate and is an important mechanism for CD8(+) T cell-independent transplant arteriosclerosis in the absence of CD40-CD154 costimulation.

Animals↗
PubMed2001

Paper alert. Immunology.

A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in immunology.

Allergy and Immunology↗
PubMed2000

Nondepleting anti-CD4 monoclonal antibody enhances the ability of oral alloantigen delivery to induce indefinite survival of cardiac allografts: oral tolerance to alloantigen.

BACKGROUND: We examined whether oral administration of alloantigen could induce the prolonged survival of cardiac allografts. METHODS: Hearts from CBK (H2k+Kb) transgenic or (C57BL/10xCBA)F1 (H2bxH2k) mice were transplanted into CBA (H2k) recipients pretreated orally with 1 x 10(7) donor splenocytes in the presence or absence of a nondepleting anti-CD4 (YTS 177, 200 microg/dose). RESULTS: Modest prolongation of CBK cardiac grafts was induced in CBA mice fed with multiple doses of CBK splenocytes (MST 42 days compared with controls fed with syngeneic CBA splenocytes, 12 days). When the CD4 monoclonal antibody, YTS177, was administered for 2 days before the first oral delivery of CBK splenocytes, all mice accepted their grafts indefinitely (MST > 100 days versus mice treated with anti-CD4 alone, 11.5 days). To determine if feeding multiple doses of alloantigen was essential, CBA mice were given CBK splenocytes orally on a single occasion in combination with the anti-CD4. The majority of the grafts survived indefinitely (MST >100 days). This oral treatment regimen also induced indefinite prolongation of (C57BL/10xCBA)F1 cardiac grafts. CONCLUSION: The induction of unresponsiveness by oral administration of alloantigen can be augmented by a nondepleting anti-CD4, YTS177, when given before the first oral delivery of allogeneic cells.

Administration, Oral↗
PubMed2000

Differential role for competitive reverse transcriptase-polymerase chain reaction and intracellular cytokine staining as diagnostic tools for the assessment of intragraft cytokine profiles in rejecting and nonrejecting heart allografts.

The early and reliable diagnosis of allograft rejection is a difficult task and the assessment of cytokine expression in the grafts can be a helpful parameter. We have compared competitive reverse transcriptase-polymerase chain reaction (RT-PCR) with intracellular cytokine staining by flow cytometry as tools to measure cytokine expression in rejecting and nonrejecting murine cardiac allografts. Both techniques gave comparable results for cytokine expression in rejecting allografts and syngeneic controls. Grafts from mice pretreated with anti-CD4 antibody and donor-specific blood transfusion showed a marked reduction in cytokine expression, as assessed by competitive RT-PCR, even though a cellular infiltrate was present in the graft. In contrast, the cytokine production measured by intracellular cytokine staining of the isolated graft-infiltrating cells was high and exceeded even that of the rejecting allografts. We conclude that intracellular cytokine staining of graft-infiltrating leukocytes by flow cytometry does not necessarily reflect accurately the cytokine milieu in the graft. This technique might therefore have a limited clinical application in contrast to competitive RT-PCR for the differentiation between graft acceptance and graft rejection.

Animals↗
PubMed1999

Evidence for immune regulation in the induction of transplantation tolerance: a conditional but limited role for IL-4.

Most experimental models of allograft tolerance depend on manipulation of immune responses at the time of transplant. In such systems, the graft itself probably plays an important role in the induction of unresponsiveness but as a consequence may suffer immune mediated damage. Ideally, recipients would be made specifically unresponsive before transplant such that the graft is protected from the outset. In this report, we demonstrate that CBA mice pretreated with donor-specific transfusion plus anti-CD4 Ab 28 days before transplant accept cardiac allografts indefinitely without further intervention. Adoptive transfer of spleen cells from mice with long term surviving grafts results in donor-specific graft acceptance in naive secondary recipients, indicating that tolerance in this system involves immuneregulation. Regulation develops as a result of the pretreatment protocol alone, since transfer of cells from pretreated but untransplanted mice to naive recipients also leads to prolonged allograft survival without additional therapy. Neutralizing IL-4 at the time of tolerance induction had no effect on graft outcome in primary recipients. However, removal of IL-4 from the adoptive transfer donors at the time of tolerance induction prevented long term engraftment in the majority of secondary recipients. Our data demonstrate that pretreatment of transplant recipients can establish immune regulation powerful enough to override the responses of an intact immune repertoire and that under stringent conditions at least, development of this regulatory population may in part be dependent on IL-4.

Adoptive Transfer↗
PubMed1997

The induction of operational tolerance is not prevented by simultaneous administration of cyclosporin A1.

In this study, the effect of combining anti-CD4 monoclonal antibody (mAb) and cyclosporin (CyA) therapy at the time of transplantation was examined. A mouse cardiac allograft model was used. Anti-CD4 mAb administered perioperatively induces long-term survival. The addition of a short course of CyA given subcutaneously in a regimen of either a high-dose treatment or a standard dose treatment to the anti-CD4 mAb treatment protocol did not have a detrimental effect on graft survival. Despite having no significant effect on graft survival, the addition of CyA to the treatment protocol did result in a significant decrease in the level of IL-2 present in the hearts 7 days after transplantation. The decrease in IL-2 production was directly related to the presence of CyA in vivo. When CyA treatment was continued throughout the period during which unresponsiveness to the graft is induced by anti-CD4 mAb therapy, 50% of the grafted hearts were rejected once the CyA was discontinued. In conclusion, the combined use of anti-CD4 mAb therapy and CyA did not have a negative effect on graft survival in this model when the two agents were used concurrently at the time of transplantation.

Animals↗
PubMed1996

Kinetics of induction of transplantation tolerance with a nondepleting anti-Cd4 monoclonal antibody and donor-specific transfusion before transplantation. A critical period of time is required for development of immunological unresponsiveness.

The combination of a depleting anti-Cd43 monoclonal antibody (mAb) and a single donor-specific transfusion before transplantation has been shown to induce operational transplantation tolerance in the majority of cardiac allograft recipients in a mouse model. To examine a protocol which might be more clinically relevant, we have modified this tolerance-inducing protocol by substituting the depleting with a nondepleting anti-Cd4 mAb. We show that this form of pretreatment can also induce immunologic unresponsiveness in most recipients (C3H/He, H2(k)), provided a critical period of time, in this case 28 days, is allowed between pretreatment and transplantation of a fully mismatched heart graft (H2(b)). When only 1 or 2 weeks were allowed between pretreatment and transplantation, only slight graft prolongation was obtained when compared with recipients receiving anti-Cd4 mAb alone, at these time points. Maintenance of tolerance in this model was due, at least in part, to active mechanisms as immunologic unresponsiveness to donor antigens could be transferred to naive syngeneic mice by splenocytes from recipients bearing long-term functioning grafts. These findings suggest that a population of regulatory cells develop after pretreatment with nondepleting anti-Cd4 mAb and donor-specific transfusion, and that it takes at least 1 month for these cells to expand and effectively drive the recipient's immune system toward immunologic unresponsiveness.

Animals↗
PubMed1996

Expression of granzyme A and perforin in mouse heart transplants immunosuppressed with donor-specific transfusion and anti-CD4 monoclonal antibody.

Granzyme A and perforin are produced by activated cytotoxic T lymphocytes and their expression correlates with the appearance of cytotoxicity. Using in situ hybridization and immunohistochemistry, we examined the phenotype of cellular infiltration and the appearance of granzyme A+ and perforin+ cells in a mouse cardiac transplant model where the recipients were pretreated with donor-specific transfusion, anti-CD4 monoclonal antibody, or both. While the profiles of cellular infiltration failed to correlate with graft survival, tolerized grafts, as compared with untreated allografts, showed a decreased frequency of granzyme A and perforin expression. These functional markers of cytotoxic T lymphocytes can differentiate between rejecting and indefinitely surviving grafts and may be of value in dissecting the immunological events involved in tolerance induction.

Acute Disease↗
PubMed1996

The Th1/Th2 paradigm and the allograft response.

Although Th1- and Th2-type cytokine profiles have been associated with rejection and tolerance respectively, this paradigm may not be completely accurate. Instead, recent studies suggest that there could be a hierarchy of T-cell growth factors with regard to their ability to block tolerance and induce rejection (rather than a polarized Th1/Th2 demarcation).

Animals↗
PubMed1996

Ischemia-reperfusion-induced muscle damage. Protective effect of corticosteroids and antioxidants in rabbits.

We examined the potential protective effect of pretreatment with corticosteroids or antioxidants (ascorbic acid or allopurinol) in rabbits with reperfusion-induced damage to skeletal muscle after ischemia. 4 hours of limb ischemia induced by a pneumatic tourniquet, followed by reperfusion for 1 hour, caused a considerable amount of ultrastructural damage to the anterior tibialis muscles accompanied by a rise in circulating creatine kinase activity. Pretreatment of animals with depomedrone by a single 8 mg bolus injection led to a preservation of the anterior tibialis structure on both light and electron microscopy. High-dose continuous intravenous infusion with ascorbic acid (80 mg/hr) throughout the period of ischemia and reperfusion also preserved skeletal muscle structure, although allopurinol in various doses had no protective effect. These data are fully compatible with a mechanism of ischemia/reperfusion-induced injury to skeletal muscle, involving generation of oxygen radicals and neutrophil sequestration and activation. They also indicate that damage to human skeletal muscle caused by prolonged use of a tourniquet is likely to be reduced by simple pharmacological interventions.

Allopurinol↗
PubMed1995

Donor-recipient microchimerism is not required for tolerance induction following recipient pretreatment with donor-specific transfusion and anti-CD4 antibody. Evidence of a clear role for short-term antigen persistence.

There is considerable current interest in the possibility that long-term graft acceptance in clinical solid-organ transplantation might be dependent upon the development of a microchimeric state between the donor and recipient. This possibility has been prompted by the observation that in some transplant patients cells of donor origin can be detected in peripheral sites such as the skin, and it has been proposed that these cells play an essential role in maintaining graft survival. The hypothesis that peripheral microchimerism is an absolute requirement for the long-term survival of solid-organ allografts was tested in a well-characterized model of transplantation tolerance in which adult recipient mice are pretreated 28 days before transplant with a single donor-specific transfusion under the cover of a depleting anti-CD4 antibody. Mice pretreated with this protocol accept donor-specific cardiac allografts (MST > 100 days) but reject those of a third party (MST 16.5 days). The protocol leads to operational tolerance in the long term in that donor-specific skin grafts show prolonged survival while those from a third party strain are rejected acutely. Since peripheral blood contains haematopoietic stem cells we speculated that the success of the anti-CD4/DST protocol might be dependent on the development of microchimerism. To address this possibility the DST was irradiated before administration under anti-CD4 antibody cover in order to prevent donor stem cells in the transfusion from establishing a microchimeric state in the recipient animals. Mice in this group rejected their grafts acutely (MST 12 days), suggesting indeed that stem cells might be very important in the success of this model. However, when the protocol was modified by giving three additional doses of irradiated whole blood to increase the possibility that recipient T cells would be engaged during antibody-induced immunocompromise, graft prolongation was restored (MST > 100 days). These results demonstrate that persistence of donor antigen at the time of anti-CD4 antibody treatment is critical for the induction of unresponsiveness in this model and show that microchimerism is not an absolute requirement for long-term graft survival.

Animals↗
PubMed1995

Transplantation tolerance induced by antigen pretreatment and depleting anti-CD4 antibody depends on CD4+ T cell regulation during the induction phase of the response.

Adult mice pretreated with donor-specific transfusion and depleting anti-CD4 antibody 28 days before transplant accept fully allogeneic heart grafts and become specifically tolerant without further treatment. The induction of tolerance in this model is not simply a function of CD4+ T cell ablation, but appears to depend on residual CD4+ T cells which escape depletion and engage donor alloantigen during a transient period of antibody blockade. To test the hypothesis that these CD4+ T cells might be responsible for regulating immune responses toward the graft, mice were reconstituted with naive recipient leukocytes at various times after pretreatment. Reconstitution either shortly after pretreatment or shortly after transplant had little effect on graft survival. However, when pretreated mice were given an additional dose of depleting anti-CD4 antibody at the time of transplant to target putative regulatory cells, naive leukocytes were able to cause acute graft rejection. These data suggest that in clinical transplantation specific T cell regulation might develop following pretreatment with antigen and non-depleting anti-CD4 antibodies. Such an approach could provide donor-specific unresponsiveness prior to transplant without the risks associated with sustained CD4+ T cell depletion.

Animals↗
PubMed1994

Induction of operational tolerance by random blood transfusion combined with anti-CD4 antibody therapy. A protocol with significant clinical potential.

Previous work from this laboratory has shown that donor-specific tolerance can be achieved in a mouse heart model if recipients are pretreated with a donor-specific blood transfusion (DST) in combination with a depleting anti-CD4 antibody. The advantage of this approach instead of simply using the antibody alone at the time of transplantation is that the nonspecific immunosuppressive effects of the antibody have largely decayed by the time of transplant such that donor-specific, rather than total, unresponsiveness results. However, this approach would not be applicable to clinical cadaveric transplantation since donor-specific transfusion at a specified time before transplant would not be possible. In an attempt to address these problems we have sought to determine (A) whether the state of unresponsiveness established by the anti-CD4/DST protocol could be maintained by repeated exposure only to the tolerizing antigen; (B) whether unrelated or random transfusion (RT) could substitute for DST in the anti-CD4/antigen pretreatment protocol, and (C) whether these two approaches could be successfully combined to provide an "umbrella unresponsiveness" that could be maintained until the time of transplant. Our data show, first, that antigen rechallenge without further antibody treatment can maintain a state of unresponsiveness to alloantigen; second, that random blood transfusion given under the cover of anti-CD4 monoclonal antibody leads to indefinite allograft survival and true tolerance in the long-term; and third, that once established by random transfusion under anti-CD4 cover, unresponsiveness can be maintained for an extended period by random transfusion alone. These results suggest that random blood transfusion combined with anti-CD4 monoclonal antibody therapy might be considered as a possible approach to the induction of specific unresponsiveness in clinical transplantation.

Animals↗
PubMed1994

Nondepleting anti-CD4 antibodies in transplantation. Evidence that modulation is far less effective than prolonged CD4 blockade.

CD4+ T cells are obvious targets for immunotherapy since they appear to be pivotal in rejection responses. Current interest in clinical transplantation is focused on the potential use of nondepleting anti-CD4 antibodies largely because depletion of CD4+ T cells may lead to prolonged periods of nonspecific immunosuppression. We have examined the efficacy of two nondepleting antibodies, KT6 and YTS 177.9, in a mouse cardiac allograft model. KT6 causes abrupt and prolonged occupation of CD4 molecules in vivo, while YTS 177.9 results in rapid and almost complete modulation of CD4 from the cell surface. In identical perioperative two-dose protocols, equivalent doses of KT6 were more effective than YTS 177.9 (MST 58 days and 24 days, respectively). When the treatment protocols were redesigned to include one or two additional doses of antibody, given as CD4 molecules were either released from blockade (KT6) or re-expressed following modulation (YTS177.9), the YTS 177.9 protocol led only to a slight improvement in graft survival (MST 51 days), whereas the modified KT6 regimen gave indefinite survival in 100% of the recipients. These data clearly show that modulating anti-CD4 antibodies may be far less effective than antibodies that effect prolonged CD4 occupation, a significant observation especially in relation to the proposed clinical use of the antibody OKT4A, which appears to cause modulation rather than CD4 blockade.

Animals↗
PubMed1992

Isolated HLA-DP mismatches between donors and recipients do not influence the function or outcome of renal transplants.

The matching of donors and renal graft recipients for human leukocyte antigens A, B, and DR has been shown to exert beneficial effects on the outcome of transplantation. Until the advent of polymerase chain reaction amplification-based genotyping, the effect of HLA-DP compatibility on graft survival could not be thoroughly investigated. HLA-DP compatibility has been determined in three living-related transplants and 34 cadaveric transplants for donor-recipient pairs matched for HLA-DR and -DQ. The effect of DP mismatching on graft survival and function was assessed. No clear benefit from matching donor and recipient for HLA-DP could be discerned.

Base Sequence↗