Alloantigen-specific Immune Responses Research Articles

Thioredoxin priming prolongs lung allograft survival by promoting immune tolerance.

Tolerance to allograft antigen is the major challenge and final goal of transplant medicine. Our previous study demonstrated that thioredoxin-1 (Trx) priming of donor lung significantly protected allogeneic lung graft. To determine whether Trx priming of donor lung inhibits allograft rejection, extends allograft survival and induces immune tolerance, orthotopic left lung transplantation was performed from Lewis to Sprague-Dawley rats without immunosuppression. Donor lungs were primed with Trx at 4°C for 4 hr prior to transplantation. After up to 37 days post-transplantation, allograft lung morphology, recipient T cell and humoral alloantigen-specific immune responses were examined. We found that Trx-primed lungs exhibited much reduced acute rejection and associated lung injuries resulting in loss of graft functional area at 5-37 days post-transplant in contrast to the control groups. CD4+ T cells from the recipients with Trx-primed grafts responded to the stimulation of dendritic cells (DCs) of donor origin, in contrast to DCs from the third party, with significantly reduced proliferation. Consistent with above findings, we observed that CD4+Foxp3+ regulatory T cells in spleen cells from the recipients with Trx-primed grafts were significantly increased compared to controls, and CD4+ T cells from the recipients with Trx-primed grafts produced much higher levels of immunosuppressive cytokine, IL-10 when stimulated with allogeneic donor DCs. In addition, humoral immune tolerance was also induced as there was no significant increase levels of serum antibodies against donor antigens in Trx-lung recipients when re-challenged with allogeneic donor antigens. Our results demonstrate that one-time Trx-priming of donor lung grafts prior to transplantation significantly prolongs the survival of the grafts through inducing or promoting cellular and humoral alloantigen-specific immune tolerance, which might be associated with the induction of immunosuppressive regulatory T cells.

Topical inhibition of T cell costimulatory pathways in draining lymph nodes may suppress allograft rejection

Topical immune suppression is an attractive and practical therapeutic option to prolong survival time of allografts, before the appearance of new agent with higher immunosuppressive efficacy and lower undesirable side effects. The initiation of rejection and outcome of allografts is principally mediated by alloantigen reactive T cells. The activation of T cells requires at least two signals, first is T-cell receptor signal and second is costimulatory signal. T cells that encounter antigen without the appropriate costimulatory signal become anergy or tolerance. Migration of alloantigen-bearing dendritic cells into the T-cell zone of secondary lymphoid tissues, which are essential for primary alloimmune responses, effectively induces T-cell activation and expansion with the presence of two signals. Draining lymph nodes are the promising targets for topical immune suppression, as disrupting lymphatic drainage from the transplanted graft to lymph nodes prevented rejection of skin allografts and lymphadenectomy prolong the survival time of skin and corneal allografts in experimental animals. Therefore, we hypothesize that inhibition of T cell costimulatory pathways in draining lymph nodes could impair the alloantigen-specific immune response and reduce systemic immunosuppressive drugs dose for allografts survival. Further investigations are required to identify most efficient way for draining lymph nodes transfer of costimulatory molecule gene or topical drug administration of costimulatory inhibitors to draining lymph nodes.

Generation of mesenchymal stromal cells in the presence of platelet lysate: a phenotypic and functional comparison of umbilical cord blood- and bone marrow-derived progenitors

Mesenchymal stromal cells are employed in various different clinical settings in order to modulate immune response. However, relatively little is known about the mechanisms responsible for their immunomodulatory effects, which could be influenced by both the cell source and culture conditions. We tested the ability of a 5% platelet lysate-supplemented medium to support isolation and ex vivo expansion of mesenchymal stromal cells from full-term umbilical-cord blood. We also investigated the biological/functional properties of umbilical cord blood mesenchymal stromal cells, in comparison with platelet lysate-expanded bone marrow mesenchymal stromal cells. The success rate of isolation of mesenchymal stromal cells from umbilical cord blood was in the order of 20%. These cells exhibited typical morphology, immunophenotype and differentiation capacity. Although they have a low clonogenic efficiency, umbilical cord blood mesenchymal stromal cells may possess high proliferative potential. The genetic stability of these cells from umbilical cord blood was demonstrated by a normal molecular karyotype; in addition, these cells do not express hTERT and telomerase activity, do express p16(ink4a) protein and do not show anchorage-independent cell growth. Concerning alloantigen-specific immune responses, umbilical cord blood mesenchymal stromal cells were able to: (i) suppress T- and NK-lymphocyte proliferation, (ii) decrease cytotoxic activity and (iii) only slightly increase interleukin-10, while decreasing interferon-gamma secretion, in mixed lymphocyte culture supernatants. While an indoleamine 2,3-dioxygenase-specific inhibitor did not reverse mesenchymal stromal cell-induced suppressive effects, a prostaglandin E(2)-specific inhibitor hampered the suppressive effect of both umbilical cord blood- and bone marrow-mesenchymal stromal cells on alloantigen-induced cytotoxic activity. Mesenchymal stromal cells from both sources expressed HLA-G. Umbilical cord blood- and bone marrow-mesenchymal stromal cells may differ in terms of clonogenic efficiency, proliferative capacity and immunomodulatory properties; these differences may be relevant for clinical applications.

G to C transition at position −173 of MIF gene of the recipient is associated with reduced relapse rates after allogeneic stem cell transplantation

Pro-inflammatory and dendritic cell-activating properties of macrophage migration inhibitory factor (MIF) suggest a potentially important role for MIF in alloantigen-specific immune responses after allogeneic stem cell transplantation (allo-SCT). We tested whether MIF −173 G/C gene polymorphism of donor or patient had impacts on the outcomes after allo-SCT. Four hundred and fifty-four donor–patient pairs were genotyped and mortality, relapse, and development of complications were analyzed. Patient but not donor MIF −173∗C allele was associated with improved overall survival (OS) (5 years: 60.8% versus 46.3%, p = 0.042) and disease free survival (DFS) (5 years: 55.4% versus 39.5%; p = 0.014) due to a reduction in relapse (day 2000: 22.8% versus 42.0% p = 0.006) but not due to decreased transplantation-related mortality (TRM) ( p = 0.44). Multivariate analysis proved patient −173∗C allele as an independent factor for reducing relapse after allo-SCT ( p = 0.023). Subgroup analysis showed a clear MIF −173∗C allele-related reduction in relapse for those patients who did not receive T cell depleted (TCD) SCT ( p = 0.01) in contrast to patients receiving TCD SCT ( p = 0.20). In summary, patient MIF −173∗C allele may be linked to specific, yet unrevealed functions in tumor biology and graft versus leukemia and lymphoma effects and potentially presents a novel prognostic marker for patient-tailored counseling and therapy in allo-SCT.

Novel Vaccination Strategy To Reduce Alloantigen Specific Responses

Vaccinations are generally performed to enhance alloantigen specific immune responses. However, whether it can be utilized to dampen alloantigen specific immune responses is not known. Therefore, we tested the hypothesis that vaccination of donors with host-derived CD8α+ dendritic cells (DCs), which are known to be tolerogenic, will reduce host-specific donor T cell responses. We vaccinated donor (BALB/c) mice with host (B6) bone marrow (BM) derived CD8α+DCs. Both unvaccinated donors and those vaccinated with CD8α- DCs served as controls.

Phenotypical and Functional Characterization of Umbilical Cord Blood-Derived Mesenchymal Stromal Cells Expanded in the Presence of Platelet Lysate and Comparison with Their Bone Marrow-Derived Counterpart

The presence of mesenchymal progenitors in full-term umbilical cord blood (UCB) has been object of discussion in recent years, as attempts to obtain these cells have either failed or yielded low frequency of mesenchymal stromal cells (MSCs). MSCs have been so far mainly expanded in vitro in the presence of fetal calf serum (FCS), which potentially carries the risk of both transmitting zoonoses and causing immune reactions against animal proteins. For these reasons, alternative culture supplements, devoid of animal components, such as platelet lysate (PL), have been tested, allowing efficient MSC isolation and expansion from bone marrow (BM). In this study, we tested the ability of PL-additioned medium to isolate and expand ex vivo MSCs from full-term UCB (UCB-MSCs) and we characterized these cells in terms of clonogenic efficiency, proliferative capacity, morphology, immunophenotype, differentiation potential and biosafety profile, comparing these characteristics with those of PL-expanded BM-MSCs. Moreover, we focused our attention on immunoregulatory properties of UCB-MSCs on alloantigen-specific immune responses and on the mechanisms by which these cells exert their effect. Ten UCB units (median volume 45 ml, range 40–60), from full-term deliveries, were selected according to the following criteria:total nucleated cell (TNC) count ranging from 500 to 750 ×106;isolation performed within 24 hours after delivery;overall cell viability > 75%, investigated by 7-amino-actinomycin D (7-AAD) and Aldeflour (ALDH).Two of the 10 UCB units (20%, UCB3 and UCB6) gave rise to MSC-like clones, which were expanded ex vivo and characterized. UCB-MSCs displayed the typical morphology, immunephenotype and differentiation capacity into osteoblasts and adypocytes reported in the literature. Although displaying a rather low clonogenic efficiency, UCB-MSCs showed to have a higher proliferative potential compared to BM-MSCs, as demonstrated by the calculated cumulative cell counts from P0 to P5. Thereafter, UCB3- and UCB6-MSCs displayed a progressive decrease in proliferative capacity, until they reached senescence after 83 (P10) and 90 (P11) days of culture. The cells progressively died during the senescence period, without showing any alteration in morphology or proliferative rate. The lack of spontaneous transformation into tumor cells was demonstrated by both the absence of telomerase activity and hTERT transcripts and by molecular karyotyping through array-Comparative Genomic Hybridization (array-CGH) assay. The immune-regulatory effect of UCB-MSCs on alloantigen-specific immune response in mixed lymphocyte culture (MLC) was investigated, together with some of the mechanisms potentially responsible for this effect, including PGE2 production and IDO activity. We found that, similarly to BM-MSCs, UCB-MSCs expanded in PL are able to:strongly inhibit alloantigen-induced lymphocyte subset (CD3+, CD4+, CD8, CD3negCD56+ NK lymphocytes) proliferation;decrease alloantigen-induced cytotoxic activity;increase secretion of IL-6 and IL-10 in MLC supernatant.While the addition of BM-MSCs to MLC increased the percentage of CD4+CD25+FoxP3+T cells, the addition of UCB-MSCs did not result in any increase of this cell subset. Moreover, we found that the immune modulation of UCB-MSCs is apparently due to PGE2 production, while the addition of IDO-specific inhibitor was not able to reverse the suppressive effect exerted by MSCs. Altogether, these data indicate that relevant differences exist between UCB- and BM-MSCs, ex vivo cultured in the presence of PL, in terms of clonogenic efficiency, proliferative capacity and immunomodulatory properties. These aspects may be relevant for the clinical application of UCB-MSCs.

Haemorrhage produces depressions in alloantigen-specific immune responses in the mouse through activation of suppressor T cells

The development of cell-mediated and humoral immune responses in BALB/c mice (H-2d) directed toward El4 cells (H-2b) was suppressed (cell-mediated cytotoxicity, 40-50% of control; antibody titres 127 +/- 17 versus 287 +/- 17 in controls) following haemorrhage of 30% total blood volume. This haemorrhage-induced depression of immune response can be transferred to normal recipients with T cells (3 x 10(7] from haemorrhaged syngeneic donors. Flow microfluorimetry (FMF) analysis showed no shift in CD8:CD4 ratios following haemorrhage. These results suggest that haemorrhage suppresses immune response through activation of suppressor T cells.

Prevention of Allograft Tolerance by Bacterial Infection with Listeria monocytogenes

Exposure to certain viruses and parasites has been shown to prevent the induction of transplantation tolerance in mice via the generation of cross-reactive memory T cell responses or the induction of bystander activation. Bacterial infections are common in the perioperative period of solid organ allograft recipients in the clinic, and correlations between bacterial infections and acute allograft rejection have been reported. However, whether bacterial infections at the time of transplantation have any effect on the generation of transplantation tolerance remains to be established. We used the Gram-positive intracellular bacterium Listeria monocytogenes (LM) as a model pathogen because its effects on immune responses are well described. Perioperative LM infection prevented cardiac and skin allograft acceptance induced by anti-CD154 and donor-specific transfusion in mice. LM-mediated rejection was not due to the generation of cross-reactive T cells and was largely independent of signaling via MyD88, an adaptor for most TLRs, IL-1, and IL-18. Instead, transplant rejection following LM infection was dependent on the expression of the phagosome-lysing pore former listeriolysin O and on type I IFN receptor signaling. Our results indicate that bacterial exposure at the time of transplantation can antagonize tolerogenic regimens by enhancing alloantigen-specific immune responses independently of the generation of cross-reactive memory T cells.

Donor age intensifies the early immune response after transplantation

Increasing donor age is associated with reduced graft function. We wondered if donor age may not only affect intrinsic function but also alter the immune response of the recipient. Kidneys from young and old F-344 rats (3 vs 18 months) were transplanted into bilaterally nephrectomized young Lewis recipients and compared with age-matched controls (follow-up: 6 months). Renal function and structural changes were assessed serially in both native kidneys and allografts. Host alloreactivity, graft-infiltrating cells, and their inflammatory products were determined at intervals to examine the correlation of immune response and donor age. Functional and structural deterioration had advanced significantly in older allografts compared with age-matched native controls, whereas differences between young allografts and native controls of similar age were only minor. Changes in grafts from elderly rats were associated with a more intense host immune response early post-transplant (up to 1 month) reflected by significantly higher numbers of peripheral T and B cells, increased T-cell alloreactivity and modified cytokine patterns associated with elevated frequencies of intragraft dendritic cells, B cells, and CD31+ cells. By 6 months, recipients of young donor grafts produced comparable or more intense alloantigen-specific immune responses. Older donor grafts elicit a stronger immune response in the early period after transplantation.

Optimization of in vitro expansion of human multipotent mesenchymal stromal cells for cell‐therapy approaches: Further insights in the search for a fetal calf serum substitute

There is great interest in mesenchymal stromal cells (MSCs) for cell-therapy and tissue engineering approaches. MSCs are currently expanded in vitro in the presence of fetal calf serum (FCS); however, FCS raises concerns when used in clinical grade preparations. The aim of this study was to evaluate whether MSCs expanded in medium supplemented with platelet-lysate (PL), already shown to promote MSC growth, are endowed with biological properties appropriate for cell-therapy approaches. We confirm previously published data showing that MSCs expanded in either FCS or PL display comparable morphology, phenotype, and differentiation capacity, while PL-MSCs were superior in terms of clonogenic efficiency and proliferative capacity. We further extended these data by investigating the immune-regulatory effect of MSCs on the alloantigen-specific immune response in mixed lymphocyte culture (MLC). We found that MSCs-PL are comparable to MSCs-FCS in their capacity to: (i) decrease alloantigen-induced cytotoxic activity; (ii) favor differentiation of CD4+ T-cell subsets expressing a Treg phenotype; (iii) increase early secretion of IL-10 in MLC supernatant, as well as induce a striking augmentation of IL-6 production. As compared with MSCs-PL, MSCs-FCS were more efficient in suppressing alloantigen-induced lymphocyte subset proliferation and reducing early IFNgamma-secretion. Resistance to spontaneous transformation into tumor cells of expanded MSCs was demonstrated by molecular karyotyping and maintenance of normal morphology/phenotype after prolonged in vitro culture. Our data support the immunological functional plasticity of MSCs and suggest that MSCs-PL can be used as an alternative to MSCs-FCS, although these latter cells might be more suitable for preventing/treating alloreactivity-related immune complications.

Platelet-Lysate for In Vitro Expansion of Human Multipotent Mesenchymal Stromal Cells in Approaches of Cell-Therapy.

There is large interest in the use of mesenchymal stromal cells (MSCs) in approaches of cell-therapy and tissue engineering. MSCs are currently expanded in vitro in the presence of fetal calf serum (FCS); however, FCS raises concerns in the case of clinical grade cellular preparations because of the theoretical risk of transmission of zoonoses and triggering immune reactions in the host. Therefore, the identification of a serum-free medium appropriate for both the extensive expansion necessary to reach the large numbers of MSCs required for clinical application, and the exclusion of risks connected with the use of animal products, is warranted. Aim of this study was to evaluate whether MSCs expanded in medium supplemented with platelet-lysate (PL) are endowed with biological properties appropriate for cell-therapy approaches. MSCs were generated from bone-marrow of 8 healthy hematopoietic stem cell donor; 4 different culture conditions were tested:10 % FCS;5% PL;2,5% PL;1% PL.MSCs were harvested when reaching ≥ 80% confluence and replated for expansion at 4.000 cells/cm² until passage 5. CFU-F frequency, proliferative capacity, morphology, surface phenotype and differentiation capacity were evaluated. In particular, the immune regulatory effect on alloantigen-specific immune response, the kinetics of cytokine production and the resistance to spontaneous transformation into tumor cells of MSC expanded in the presence of either PL or FCS were investigated. Our results demonstrate that MSCs expanded in either FCS or PL display comparable morphology, phenotype and differentiation capacity, while PL-MSCs were superior in terms of clonogenic efficiency and proliferative capacity. Immune-regulatory effect of MSCs was investigated on alloantigen-specific immune response in mixed lymphocyte culture (MLC). We found that MSCs-PL are comparable to MSCs-FCS in their capacity to:decrease alloantigen-induced cytotoxic activity;favor differentiation of CD4+ T-cell subsets expressing Treg phenotype;increase early secretion of IL-10 in MLC supernatant, as well as to induce a striking augmentation of IL-6 production.As compared with MSCs-PL, MSCs-FCS were more efficient in suppressing alloantigen-induced lymphocyte subset proliferation and in reducing early IFNg-secretion. Resistance to spontaneous transformation into tumor cells of expanded MSCs was demonstrated by both molecular karyotyping (array-comparative genomic hybridization) and maintenance of normal morphology/phenotype after prolonged in vitro culture. Our data support the hypothesis of a remarkable immune functional plasticity of human MSCs and suggest that the use of MSCs-PL, which seem to be endowed with a relatively low immune suppressive activity, could be more appropriate in approaches of reparative/regenerative cell-therapy or in strategies aimed at improving hematopoietic/immune recovery after hematopoietic stem cell transplantation (HSCT). On the contrary, as MSCs-FCS seem to display a more pronounced immune suppressive function, they might be more suitable for preventing or treating alloreactive-related immune complications, such as severe Graft-versus-host disease (GvHD) in HSCT and graft rejection in HSCT and solid organ transplantation.

Allo-specific T-Cells Encoding for Viral IL-10 Exert Strong Immunomodulatory Effects in vitro but Fail to Prevent Graft Rejection

Recently, we demonstrated the capacity of allo-specific gene-engineered T lymphocytes as transport vehicle for therapeutic transgenes into allografts. In this study, the influence of viral IL-10 as therapeutic transgene was addressed. Lewis rat T-cell lines specific for DA rat alloantigens were engineered to express vIL-10 by using a retroviral gene expression system. Like T regulatory 1 cells, vIL-10 transgenic T lymphocytes express the phenotype CD4(+)25(+) and secrete, in addition to vIL-10, rat IL-10 and IFN-gamma but no IL-4. First, the capacity of vIL-10 transgenic T-cell lines to modulate alloantigen-specific immune responses was evaluated in vitro. In comparison to control MLR with no transgenic cells or equal numbers of control T(EGFP)-lymphocytes, the proliferation as well as production of IFN-gamma by naive responder cells were significantly diminished. Despite this regulatory capacity in vitro, T(vIL-10)-lymphocytes were not able, either alone or in combination with suboptimal doses of Cyclosporine A, to prolong the survival of either DA rat cardiac or renal allografts in Lewis rat recipients. These data demonstrate that intra-graft IL-10 over-expression is not sufficient to prolong allograft survival in a high-responder strain combination and that the regulatory capacity of T cells in vitro does not predict their in vivo efficiency.

Grafts from elderly donors elicit a stronger immune response in the early period posttransplantation: A study in a rat model

With a growing demand for transplants, grafts from older donors are increasingly used. However, altered immune responses associated with increasing donor age may influence graft survival. We dissected the effects of donor age on the immune response in an experimental model. Kidneys from young and old F-344 donors (3 and 18 months) transplanted into young Lewis recipients (3 months) were followed for 6 months. Renal function, structural changes, and immune activation were tested at serial time intervals. Splenocytes and peripheral blood mononuclear cells were examined by flow cytometry; alloantigen-specific intracellular IFN-γ secretion was evaluated by ELISPOT. Grafts from both young and old donors survived the observation period. The ratio of structural changes (6/1 months) increased twofold in old vs young grafts. In parallel, the ratio of renal function declined by fivefold in recipients of old donor kidneys. Most interestingly, elderly grafts produced a modified immune response: the numbers of T/B cells and alloreactive T cells increased early following the transplantation of old grafts ( P < .05). However, by 6 months, the amounts of T and B cells as well as alloantigen-specific immune responses were comparable in recipients of old versus young grafts. Older grafts elicit a stronger immune response during the early period posttransplantation. This process is associated with an increased immunogenicity in older grafts. Clinical immunosuppressive protocols need to consider these effects.

Interaction of Human Mesenchymal Stem Cells with Alloantigen-Induced T Lymphocyte Activation Favors the Differentiation of CD4+ T Cell Subsets Expressing CD25 and/or CTLA4 Molecules.

Experimental evidence and preliminary clinical studies have demonstrated that human mesenchymal stem cells (MSCs) display important immune modulatory function of potential relevant interest in the setting of allogeneic hematopoietic stem cell (HSC) transplantation. Effectiveness of MSCs in controlling severe GVHD seems to be related to the immune-regulatory role they play in suppressing alloantigen-specific T-cell activation. Aim of the present study was to extend the analysis of the mechanisms responsible for the immune regulatory effect of interaction between MSCs and alloantigen-specific immune response elicited in vitro in primary and in secondary mixed lymphocyte culture (MLC). At difference with most previously reported studies, we decided to employ non-irradiated MSCs, reasoning that irradiation might impair, beside the proliferative capacity, also the differentiation capability of MSCs and, consequently, alter their interaction pattern with lymphocyte subsets. MSC were added to primary MLC at different doses (MLC-responder-PBMC:MSC ratios = 1:1 and 10:1). Dendritic cell (DC) differentiation, lymphocyte proliferation, alloantigen-specific cytotoxic activity and differentiation of CD4+ T-cell subsets expressing CD25 and/or CTLA4 antigens were assessed in primary and secondary MLC, comparing the effect observed using third-party MSCs with that obtained employing autologous to the MLC-responder (autologous) MSCs. Results demonstrated that human MSCs: (1) strongly inhibit alloantigen-induced DC1 differentiation; (2) down-regulate, in a dose-dependent manner, alloantigen-induced lymphocyte expansion, especially that of CD8+ T cells and of NK lymphocytes; (3) favor the differentiation of CD4+ T cells co-expressing CD25 and/or CTLA4, a phenotype associated with regulatory/suppressive function of immune response; (4) cause a dose-dependent reduction of alloantigen-specific cytotoxic capacity mediated by either cytotoxic T lymphocytes or NK cells; (5) exert more effective suppressive activity on MLC-induced T-cell activation when they are allogeneic rather than autologous with respect to responder cells. In particular, higher percentages of CD4+ and of CD4+CD25+ T cells co-expressing CTLA4+ were detected when third-party, rather than autologous, MSCs were added to MLC. These data suggest that T-cell recognition of alloantigens expressed by MSCs may further facilitate the preferential differentiation of activated CD4+ T cells expressing CTLA4, a glycoprotein, known to deliver an inhibitory signal to T cells and to mediate apoptosis of previously activated T lymphocytes. Several studies previously demonstrated that MSCs exert inhibitory effect on lymphocyte activation through the release of soluble factors. Our data suggest that the preferential differentiation of CD4+CD25+ regulatory T-cell subsets may be favored by other mechanisms of MSC-mediated inhibition of alloantigen-induced effector cell activation and expansion, and, in turn, these CD4+CD25+ cells contribute to propagate and extend suppressor activity. Altogether, our results provide immunological support to the use of MSCs for prevention of immune complications related to both HSC and solid organ transplantation and to the theory that MSCs are “universal” suppressors of immune reactivity.

The pathophysiology of chronic graft-versus-host disease.

Chronic graft-versus-host disease (GVHD) still remains the most significant complication after allogeneic hematopoietic stem cell transplantation. The disease usually appears after day 100 and is characterized by signs and symptoms similar to autoimmune diseases. The pathophysiology of chronic GVHD is poorly understood because of the lack of highly satisfactory animal models and basic studies in patients. It has not been clearly determined whether the disease is a distinct entity or a continuation of acute GVHD. In experimental and clinical studies of chronic GVHD, thymic atrophy, lymphocyte depletion, and autoantibody formation have been described. Conditioning regimens and acute GVHD may disrupt thymic function and dysregulate the negative selection process of potentially autoreactive T-lymphocytes. Disruption of thymic apoptosis and failure to eliminate the majority of self-reactive lymphocytes may lead to impairment of lymphocyte homeostasis and self tolerance. Expansion and effector functions of autoreactive T-cells will then promote autoreactive B-cell activation and production of autoantibodies with target-organ damage. Chronic GVHD requires continuous CD4+ T-cell help for B-cells and is known as T-helper 2 (Th2) disease. Murine models have demonstrated the roles of interleukin (IL)-12 and IL-18 in chronic GVHD. IL-12 may cause an increase in donor CD8+ cytotoxic T-cells leading to conversion of chronic GVHD to an acute form. In contrast, IL-18 prevents chronic GVHD by decreasing numbers of CD4+ (Th2) cells and host-reactive B-cell activation and reducing alloantigen-specific immune response. Mouse and human cellular genomics coupled with advances in cell biology in donor-recipient tolerance will improve our understanding of transplantation immunology and may offer new approaches to the challenge of ameliorating chronic GVHD.

Transforming growth factor-β1 derived from biliary epithelial cells may attenuate alloantigen-specific immune responses

Immune response to liver allografts may be different from that to other organ transplants since immunological manipulation easily attenuates immune-response to liver allografts. Numerous studies on the alloantigen-specific immune response have been carried out, however, the precise mechanisms involved in this attenuation are not clear yet. Here we suggest the attenuation of alloantigen-specific immune response by TGF-beta 1 derived from biliary epithelial cells. The transforming growth factor-beta 1 (TGF-beta 1) expression in rat liver was examined immunohistologically. Rat biliary epithelial cells (BEC) were purified from the perfused liver and added to allogeneic mixed lymphocyte reaction (allo-MLR) to assess their attenuating potential on allo-MLR and alloantigen-specific cytotoxic T lymphocyte (allo-CTL) induction. Immunohistological investigation revealed the expression of TGF-beta 1 in biliary epithelial cells. Both purified biliary epithelial cells and TGF-beta 1 attenuated allo-MLR and allo-CTL induction in a dose-dependent manner, and anti-TGF-beta 1 antibody partially relieved this attenuation. This study reveals that biliary epithelial cells, the major target cells of allo-antigen specific immune response, contain TGF-beta 1 and that they have a capacity to attenuate allo-MLR and allo-CTL induction.

Transforming growth factor-β1 derived from biliary epithelial cells may attenuate alloantigen-specific immune responses

Abstract Immune response to liver allografts may be different from that to other organ transplants since immunological manipulation easily attenuates immune-response to liver allografts. Numerous studies on the alloantigen-specific immune response have been carried out, however, the precise mechanisms involved in this attenuation are not clear yet. Here we suggest the attenuation of alloantigen-specific immune response by TGF-β1 derived from biliary epithelial cells. The transforming growth factor-β1 (TGF-β1) expression in rat liver was examined immunohistologically. Rat biliary epithelial cells (BEC) were purified from the perfused liver and added to allogeneic mixed lymphocyte reaction (allo-MLR) to assess their attenuating potential on allo-MLR and alloantigen-specific cytotoxic T lymphocyte (allo-CTL) induction. Immunohistological investigation revealed the expression of TGF-β1 in biliary epithelial cells. Both purified biliary epithelial cells and TGF-β1 attenuated allo-MLR and allo-CTL induction in a dosedependent manner, and anti-TGF-β1 antibody partially relieved this attenuation. This study reveals that biliary epithelial cells, the major target cells of allo-antigen specific immune response, contain TGF-β1 and that they have a capacity to attenuate allo-MLR and allo-CTL induction.

Interleukin-12 (IL-12)-driven alloimmune responses in vitro and in vivo: requirement for beta1 subunit of the IL-12 receptor.

Interleukin-12 (IL-12) mediates its biologic activities via binding high-affinity receptors on T and natural killer cells. Although emphasis has been placed on the requirement for IL-12Rbeta2 in IL-12 bioactivity, the role of IL-12Rbeta1 is less well defined. The current study evaluated the effects of exogenous IL-12 on alloantigen-specific immune responses and determined the requirement for IL-12Rbeta1 in IL-12-mediated alloimmunity. The mouse heterotopic cardiac transplant model was employed to evaluate the effects of IL-12 on alloantigen-specific immune responses in vivo. In addition, IFN-gamma production in mixed lymphocyte cultures (MLC) supplemented with IL-12 was measured to assess the effects of IL-12 on Th1 function in vitro. Mice deficient in IL-12Rbeta1 (IL-12Rbeta1-/-) were used to determine the requirement for this receptor component in IL-12-driven alloimmune responses. Addition of IL-12 to MLC consisting of wild-type splenocytes enhanced alloantigen-specific proliferative responses and Th1 development. In contrast, IL-12 did not alter these in vitro immune parameters in IL-12Rbeta1-/- MLC. Treatment of wild-type cardiac allograft recipients with IL-12 resulted in high concentrations of serum interferon-gamma (IFN-gamma) and a 10-fold increase in IFN-gamma production by recipient splenocytes after restimulation in vitro. However, this fulminate Th1 response did not accelerate allograft rejection. Importantly, IL-12 had no effect on serum IFN-gamma or in vivo priming of Thl in IL-12Rbeta1-/- recipients. Finally, administration of IL-12 to WT allograft recipients resulted in a bimodal alloantibody response: antibody production was suppressed at high doses of IL-12, and enhanced at lower doses. IL-12 markedly enhances alloantigen-specific immune function; however, these exaggerated Th1-driven responses do not culminate in accelerated allograft rejection. Further, these data indicate that IL-12Rbeta1 is essential for the enhancement of both in vitro and in vivo alloimmune responses by exogenous IL-12.

Human kidney engraftment under the kidney capsule of the human/rat radiation chimera: A new model for the sudy of human renal allograft rejection

Increasing donor age is associated with reduced graft function. We wondered if donor age may not only affect intrinsic function but also alter the immune response of the recipient. Kidneys from young and old F-344 rats (3 vs 18 months) were transplanted into bilaterally nephrectomized young Lewis recipients and compared with age-matched controls (follow-up: 6 months). Renal function and structural changes were assessed serially in both native kidneys and allografts. Host alloreactivity, graft-infiltrating cells, and their inflammatory products were determined at intervals to examine the correlation of immune response and donor age. Functional and structural deterioration had advanced significantly in older allografts compared with age-matched native controls, whereas differences between young allografts and native controls of similar age were only minor. Changes in grafts from elderly rats were associated with a more intense host immune response early post-transplant (up to 1 month) reflected by significantly higher numbers of peripheral T and B cells, increased T-cell alloreactivity and modified cytokine patterns associated with elevated frequencies of intragraft dendritic cells, B cells, and CD31+ cells. By 6 months, recipients of young donor grafts produced comparable or more intense alloantigen-specific immune responses. Older donor grafts elicit a stronger immune response in the early period after transplantation.

Management of subdural empyema: a series of 24 cases.

Twenty four cases of subdural empyema are reviewed. The overall mortality was 17%, 18 patients were managed by burr hole and five by craniotomy or craniectomy. Antibiotic therapy was commenced once pus had been evacuated. Infection of the paranasal and mastoid sinuses was the commonest aetiological factor. Aspiration of pus through burr holes is the recommended surgical procedure with low mortality and morbidity, when combined with early diagnosis and aggressive chemotherapy.