Allogeneic Graft Rejection Research Articles

Transplantation of CD95 ligand-expressing grafts: influence of transplantation site and difficulty in protecting allo- and xenografts.

CD95 and its ligand (CD95L) have been implicated in the regulation of immune responses. Recently, it was reported that CD95L expression prevented rejection of allogeneic grafts transplanted under the kidney capsule. In contrast, we reported that enforced CD95L expression in subcutaneously grafted cells induced acute rejection even in the syngeneic or immunodeficient hosts. In this study, we investigated whether the CD95L-expressing cells could be protected from rejection when transplanted under the kidney capsule. CD95-negative cells (baby hamster kidney and L5178Y lymphoma cells) were transfected with CD95L cDNA to express functional CD95L. The cells were transplanted into skin or renal subcapsular space of immunocompetent or T cell-deficient nu/nu mice. The parental cells grew well in nu/nu or syngeneic mice but were rejected in allogeneic or xenogeneic immunocompetent mice. The CD95L transfectants were rejected when transplanted subcutaneously in all types of mice studied. However, when transplanted under the kidney capsule, they survived in nu/nu or syngeneic mice but were rejected in allogeneic or xenogeneic immunocompetent mice. These results imply that CD95L expression may not be sufficient to protect the grafts from rejection, and the survival of CD95L-bearing grafts is substantially influenced by the site of transplantation.

Localization to chromosome 22 of a gene encoding a human minor histocompatibility antigen.

In human allogeneic bone marrow transplantation, graft-vs-host disease and graft rejection can occur even if the patient and donor are genotypically matched by inheritance for HLA. By definition, these allogeneic reactions are due to disparities in minor histocompatibility Ags (minor HAs). Minor HAs are presented to T lymphocytes as peptides bound to HLA molecules, and appear to be encoded by genes throughout the genome. We derived T lymphocyte clones from the PBL of a patient suffering from chronic graft-vs-host disease after bone marrow transplant from his HLA-identical sister. Clones reactive against minor HAs were selected on the basis of reactivity with pretransplant patient cells, and absence of reactivity with donor cells. One clone (MD2) was found to use HLA-B7 as a restricting element. A plasmid vector (pHEBo) containing cDNA encoding the HLA-B7 molecule was transfected into lymphoblastoid cell lines derived from two large families that previously had been saturation mapped for hundreds of polymorphic loci. When clone MD2 was tested against family K1362, it was found to be reactive with three of four grandparents, both parents, and eight of eleven offspring. The same clone was tested with family K1331, with two of three tested grandparents reactive, one of two parents, and nine of eleven offspring. Computer analysis showed that both family segregation patterns linked to an area on the long arm of chromosome 22, localizing the gene encoding this minor HA near the platelet-derived growth factor-beta and IL-2Rbeta genes.

Prevention of Allogeneic Marrow Graft Rejection by Donor T Cells That Do Not Recognize Recipient Alloantigens: Potential Role of a Veto Mechanism

Clinical trials and experimental studies have demonstrated that donor T cells can play a critical role in preventing allogeneic marrow graft rejection. Results of a previous study showed that donor T cells were most effective for preventing rejection when they recognize an alloantigen expressed by recipient T cells and can cause graft-versus-host disease (GVHD). The present study examined models where marrow graft rejection can be prevented by donor T cells that do not recognize host alloantigens and cannot cause GVHD. Donor T cells prevented rejection of major histocompatibility complex (MHC) class I and II-disparate F1 marrow in parental recipients prepared with > or = 800 cGy total body irradiation (TBI) but not in those prepared with < or = 750 cGy TBI. In recipients prepared with high TBI exposures, rejection was mediated entirely by host CD8 cells. With lower TBI exposures, rejection was mediated by host CD4 cells and CD8 cells. These observations suggested the hypothesis that donor T cells prevent rejection mediated by host effectors that recognize donor MHC class I alloantigens but do not prevent rejection mediated by host effectors that recognize donor class II alloantigens. Consistent with this hypothesis, further experiments showed that F1 donor T cells can prevent rejection of MHC class I-disparate marrow in irradiated parental recipients but have no detectable effect on rejection of MHC class II-disparate marrow. We propose that the expression of MHC class I molecules on donor T cells makes it possible for these cells to inactivate the host response against donor class I alloantigens through a veto mechanism, whereas the absence of MHC class II molecules on murine T cells explains why these cells cannot inactivate the host response against donor class II alloantigens. Finally, donor CD4 cells and CD8 cells were equivalently effective for preventing rejection of F1 marrow in parental recipients, suggesting that veto activity is not restricted solely to the CD8 subset of murine T cells. A veto mechanism could enable donor T cells to prevent allogeneic marrow graft rejection without causing GVHD.

Prevention of allogeneic marrow graft rejection by donor T cells that do not recognize recipient alloantigens: potential role of a veto mechanism

Clinical trials and experimental studies have demonstrated that donor T cells can play a critical role in preventing allogeneic marrow graft rejection. Results of a previous study showed that donor T cells were most effective for preventing rejection when they recognize an alloantigen expressed by recipient T cells and can cause graft-versus- host disease (GVHD). The present study examined models where marrow graft rejection can be prevented by donor T cells that do not recognize host alloantigens and cannot cause GVHD. Donor T cells prevented rejection of major histocompatibility complex (MHC) class I and II- disparate F1 marrow in parental recipients prepared with &gt; or = 800 cGy total body irradiation (TBI) but not in those prepared with &lt; or = 750 cGy TBI. In recipients prepared with high TBI exposures, rejection was mediated entirely by host CD8 cells. With lower TBI exposures, rejection was mediated by host CD4 cells and CD8 cells. These observations suggested the hypothesis that donor T cells prevent rejection mediated by host effectors that recognize donor MHC class I alloantigens but do not prevent rejection mediated by host effectors that recognize donor class II alloantigens. Consistent with this hypothesis, further experiments showed that F1 donor T cells can prevent rejection of MHC class I-disparate marrow in irradiated parental recipients but have no detectable effect on rejection of MHC class II-disparate marrow. We propose that the expression of MHC class I molecules on donor T cells makes it possible for these cells to inactivate the host response against donor class I alloantigens through a veto mechanism, whereas the absence of MHC class II molecules on murine T cells explains why these cells cannot inactivate the host response against donor class II alloantigens. Finally, donor CD4 cells and CD8 cells were equivalently effective for preventing rejection of F1 marrow in parental recipients, suggesting that veto activity is not restricted solely to the CD8 subset of murine T cells. A veto mechanism could enable donor T cells to prevent allogeneic marrow graft rejection without causing GVHD.

Interactions between malignant tumor growth and allogeneic graft rejection in an experimental rat model.

We describe a combined tumor and simultaneous transplant model in rats in tended to investigate interactions between tumor growth and graft rejection. To study the influence of tumor growth on graft rejection. Novikoff hepatoma cells were injected subcutaneously into the back of Lewis rats. Eight days later, the grown solid tumor was resected, and allogeneic heart transplantation was performed. Four groups were formed, receiving 5-fluorouracil (5-FU), cyclosporin A (CsA), 5-FU + CsA, and placebo, respectively. In the corresponding groups, tumor injection was omitted. Graft survival was significantly prolonged when CsA was given 5-FU did not abrogate or augment CsA efficiency nor influence graft survival when given alone. In the corresponding control groups, graft survival was similar, thus excluding an immunomodulating effect of the prior tumor growth on graft survival. To study the reverse interaction of allogeneic graft on tumor growth, heart grafting and tumor cell injection were performed on the same day. In different groups, 5-FU, CsA, 5-FU + CsA, and placebo was given. For the control, no transplantation was carried out. The tumor was resected on the 8th postoperative day and examined by immunohistology. A slight decrease of tumor growth by 5-FU, but a marked increase by CsA were found, whereas the graft alone showed no immunomodulation.

Donor CD8 cells prevent allogeneic marrow graft rejection in mice: potential implications for marrow transplantation in humans.

Numerous experimental models have demonstrated that graft-vs.-host disease (GVHD) does not occur in irradiation chimeras when the graft does not contain mature, immunocompetent T lymphocytes, but clinical studies have shown that T cell depletion of donor marrow can be associated with a greatly increased risk of graft failure. We have developed a model where engraftment of (C57BL/6J x C3H/HeJ)F1 (B6C3) marrow in 800-cGy-irradiated (BALB/cJ x C57BL/6J)F1 (CB6) recipients depends on the presence of donor T cells in the graft. Recipients transplanted with 5.0 x 10(6) marrow cells depleted of T lymphocytes showed host lymphoid and myeloid reconstitution, whereas recipients transplanted with the same marrow plus 2.5 x 10(5) purified donor T cells showed donor reconstitution. Adding as few as 0.5 x 10(5) CD8-enriched donor T cells to marrow grafts containing 5.0 x 10(6) T cell-depleted donor cells was sufficient to enable donor reconstitution, while surviving recipients transplanted with the same marrow and 0.5-2.5 x 10(5) CD4-enriched donor cells showed only host reconstitution. To address the question of whether donor CD4 cells could facilitate engraftment under conditions where GVHD would not represent a limiting factor, engraftment of bm1 marrow was tested in major histocompatibility complex (MHC) class I-disparate B6.Ly5a recipients. Results indicated that the donor CD8-enriched population was at least fivefold more active than the CD4-enriched population for facilitating allogeneic marrow engraftment in this strain combination. Thus, the lymphokines and MHC class II-specific cytotoxic T cells generated by CD4 cells were relatively ineffective for enhancing engraftment, possibly reflecting the fact that the host T cells that contain effectors responsible for causing rejection do not express MHC class II antigens. The ability of donor CD8 cells to facilitate engraftment could reflect the activity of a cytokine uniquely elaborated after recognition of an MHC class I disparity. More likely, the graft-enhancing effect of donor CD8 cells may result from the generation of MHC class I-specific or class I-restricted cytotoxic T cells that recognize the host CD4 and CD8 cells responsible for causing rejection. The possibility remains that other mechanisms such as veto inactivation of host T cells by donor CD8 cells may also contribute to the graft-enhancing effect.

Certain Host-Donor Rat Strain Combinations Do Not Reject Brain Allografts after Systemic Sensitization

To investigate the factors related to allogenic brain graft rejection, rat cortex from either LEW-RT1l or BN-RT1n rats was transplanted into brains of several isogenic and allogenic inbred strains: F344-RT1l, LEW-RT1l, BN-RT1n, AO-RT1u, PVG-RT1c, PVG-RT1u, and PVG-RT1l. Each donor and host combination was subsequently subdivided into two subgroups. One group was systematically sensitized twice with donor skin tissue and another group served as a sham-sensitization control. Four weeks after the second sensitization, host brains were examined histologically, and the percentage volume of each graft that showed increased cellularity was estimated. Expression of major histocompatibility complex (MHC) and T cell antigens was also studied immunocytochemically. Almost all grafts in sham-sensitized animals from all groups were accepted with minimal or no reaction. However, two strains (AO-RT1u and F344-RT1l) showed considerable cell infiltration and expression of MHC antigens even without sensitization. After sensitization, almost all allogenic strain combinations showed greater signs of rejection-related responses. The severity of the tissue reaction, however, varied considerably between groups. All grafts from BN-RT1n donors were rejected severely in all host strains. For LEW-RT1l donors, grafts survived well in some host strains (BN-RT1n, AO-RT1u, PVG-RT1c, and PVG-RT1u), even with MHC + nonMHC disparity. Curiously, F344-RT1l hosts rejected LEW-RT1l grafts even though the two strains have the same MHC loci, but different minor histocompatibility (mH) loci. For both donor strains, experimental autoimmune encephalomyelitis-susceptible hosts tended to show more vigorous rejection responses. Histological data indicated that CD4+ cells were the predominant infiltrating cell type(s). These cells appeared to be primarily blood-derived macrophages and microglia. Relatively few CD8+ cells were present even in grafts with severe immune reactions. Our results suggest that MHC disparity is not the only factor affecting the survival of allogenic neural grafts, with or without systemic sensitization, and in fact plays a relatively limited role. It is suggested that susceptibility to neural graft rejection depends on a number of factors, most importantly haplotype of the donor, but also including Ir gene, host MHC allele, and host susceptibility to autoimmune disease.

EPR detection of heme and nonheme iron-containing protein nitrosylation by nitric oxide during rejection of rat heart allograft.

The paramagnetic molecule nitric oxide (NO), produced from L-arginine by a specific enzyme (NO synthase), has been shown to be involved in a surprising variety of mammalian cellular responses, including the regulation of T cell immunity to alloantigens in vitro. In cytotoxic activated macrophages, NO production results in a characteristic pattern of alteration of iron-containing enzyme function that is mimicked by exposure to NO. Electron paramagnetic resonance (EPR) studies have shown the formation of iron-nitrosyl species during macrophage activation and also during sepsis, indicating that alteration of iron-containing protein function may be the result of the well-documented tendency of NO to bind to metal ions. We have recently shown that the NO synthesis induced during alloantigenic activation of rat splenocytes inhibits lymphocyte proliferation and cytotoxic T-lymphocyte generation. This report demonstrates that iron-nitrosyl EPR signals similar to those observed in macrophages and during sepsis are present in the blood and in the grafted tissue of rats during the rejection of allogeneic (but not syngeneic) heart grafts. These signals are found in the blood and at the site of allograft rejection, but are not found in other tissues (such as spleen and lung), and are obliterated by administration of the immunosuppressant FK506. These results directly demonstrate the formation of iron-nitrosyl complexes during vascularized allograft rejection and suggest that consequent destruction of iron-containing protein function plays an important role in the rejection response.

Role of B and T lymphocytes in the specific immunosuppression induced by a protein released by a protein monocytes infected with African swine fever virus

Some immunobiological aspects of host responses to an immunosuppressive protein (p36) released by porcine monocytes upon infection with African swine fever virus were analysed in a murine system. Treatment of normal, adult C57BL/6 mice with p36 (i) significantly delayed allogenic skin graft rejection; (ii) suppressed the specific plaque-forming cell response to immunization with heterologous erythrocytes; but (iii) induced marked increases in the numbers of 'background' splenic Ig-secreting plaque-forming cells. Cytofluorometric analysis of spleen cells revealed that a considerable fraction of all B cells, as well as CD4 and CD8 T lymphocytes, undergo blast transformation after p36 treatment. The immunosuppressive effects do not seem to result from 'antigenic competition', for they cannot be induced by even higher doses of pig albumin or by culture products of non-infected pig monocytes. Suppression of specific antibody responses and stimulation of 'background' plaque-forming cells are both T cell-dependent, since they are markedly reduced in thymectomized mice and in animals treated with anti-CD4 or anti-CD8 antibodies. This suggests the relationship between non-specific stimulation and specific suppression of 'unrelated' immune responses and reinforces the notion that viral-associated immunosuppression may be due to overstimulation. The present murine experimental model may prove valuable in the study of immunosuppression associated with infection, even for microorganisms which do not infect mice.

Hyaluronic acid accumulation and redistribution in rejecting rat kidney graft. Relationship to the transplantation edema.

By using biotin-labeled proteoglycan core protein and an avidin-enzyme system, hyaluronic acid (HA) was visualized in rat kidney. In the normal kidney, HA was localized in the extracellular space of the inner medulla and increased markedly towards the papillary tip. No staining for HA was seen in the interstitial tissue of the cortex or the outer medulla. During the development of rejection of allogeneic renal grafts, a progressive increase in accumulated HA was seen in the interstitial tissue of the cortex and outer medulla. The extractable amounts of HA increased, on average, 40 times in the cortex and outer medulla; no increase was measured in the inner medulla and papilla. The relative water content of the cortex and outer medulla also increased progressively and correlated with the HA accumulation. The extractable amounts of HA in syngeneic grafts increased by day 2 and then leveled off, indicating that surgical trauma may induce some transient HA accumulation after transplantation. Interstitial accumulation of HA, a glycosaminoglycan with unique water-binding qualities, would presumably influence water transport and osmotic activity and should thereby be implicated in the normal papillary function, but also in the development of the interstitial edema of the cortex and outer medulla during rejection of renal grafts.

Accumulation of hyaluronan (hyaluronic acid) in myocardial interstitial tissue parallels development of transplantation edema in heart allografts in rats.

By using biotin-labeled proteoglycan core protein, hyaluronan (hyaluronic acid; HA) was visualized in rat heart grafts at different times (2, 4, and 6 d) after transplantation. In normal, nontransplanted hearts HA was present in the adventitia of arteries and veins and in the myocardial interstitial tissue. An increased accumulation of HA was evident in the edematous interstitial tissue, infiltrated with lymphocytes, on day 4 after allogeneic transplantation, and was even more pronounced by day 6. No apparent increase in HA was seen in syngeneic grafts. Biochemical assay of HA in heart tissue demonstrated that the myocardial content of HA had increased 60% by day 2 after transplantation in allogeneic as well as syngeneic grafts, indicating that surgical trauma may induce some HA accumulation in heart grafts. The extractable amount of HA declined during the following days in the syngeneic grafts, but increased progressively during the development of rejection in the allogeneic grafts, and increased on average three times by day 6. The relative water content also increased progressively during rejection of allogeneic grafts and correlated with the HA accumulation. The interstitial accumulation of HA, a glycosaminoglycan with unique water-binding qualities, is presumably implicated in the development of interstitial edema during rejection of heart grafts.

Evidence for differentiation of NK1+ cells into cytotoxic T cells during acute rejection of allogeneic bone marrow grafts

The ability of lethally irradiated C57BL/6 mice to acutely reject H-2d bone marrow is due to a lymphocyte population that is NK1+, ASGM1+, CD4-, CD8-, CD3+. Transfer of spleen cells from C57BL/6 mice expressing these antigens into nonresponder 129 mice adoptively transfers the ability to reject H-2d marrow grafts. The specificity of this rejection maps to the H-2D major histocompatibility complex (MHC) region. Transplantation of high doses of H-2d marrow into C57BL/6 overrides the acute rejection mechanism leading to graft survival. During growth of the graft, a cytolytic activity develops that is due to ASGM1+, CD8+ cytolytic T lymphocytes (CTLs) with H-2Ld specificity. The possibility that the ASGM1+, CD8+ CTLs are descendents of the CD3+, NK1+, ASGM1+, CD8- cells responsible for acute rejection is investigated by adoptive cell transfer experiments. We show that beige mice that lack NK1+ cells as well as the ability to acutely reject H-2d marrow fail to generate specific CTLs after transplantation with a high dose of H-2d marrow. Transfer of highly purified NK1+ cells from B6.PL-Ly-2a/Ly-3a (Lyt-2.1) into beige mice together with H-2d marrow leads to generation of Lyt-2.1 CTLs from donor NK1+ cells. These results show that specific CTLs are generated from NK1+ cells during acute marrow graft rejection.

Prevention of allogeneic bone marrow graft rejection by H-2 transgene in donor mice.

Rejection of bone marrow grafts in irradiated mice is mediated by natural killer (NK) cells and is controlled by genes linked to the major histocompatibility complex (MHC). It has, however, not been possible to identify the genes or their products. An MHC class I (Dd) transgene introduced in C57BL donors prevented the rejection of their bone marrow by NK cells in irradiated allogeneic and F1 hybrid mice expressing the Dd gene. Conversely, H-2Dd transgenic C57BL recipients acquired the ability to reject bone marrow from C57BL donors but not from H-2Dd transgenic C57BL donors. These results provide formal evidence that NK cells are part of a system capable of rejecting cells because they lack normal genes of the host type, in contrast to T cells, which recognize cells that contain abnormal or novel sequences of non-host type.

Characterization of primary T cell subsets mediating rejection of pancreatic islet grafts.

The cellular mechanisms by which pancreatic islet grafts are rejected have not been clearly defined. In order to address the roles of CD4+ and CD8+ T cells in pancreatic islet rejection, we used an adoptive transfer model in which H-2b nude mice were reconstituted with negatively selected H-2b CD4+ or CD8+ T cell subpopulations and engrafted with fully allogeneic pancreatic islet grafts. We found that primary (unprimed) CD4+ T cells mediated the rejection of pancreatic islet grafts, whereas, primary CD8+ T cells failed to do so, even though both T cell subpopulations were competent to reject skin allografts. These data indicate that primary CD4+ T cells are necessary for rejection of allogeneic pancreatic islet grafts, whereas primary CD8+ T lymphocytes are not. Implications concerning the nature of the APC involved in the initiation of the rejection response to islet allografts and the expression of MHC Ag by pancreatic islet cells are discussed.

A novel cell type responsible for marrow graft rejection in mice. T cells with NK phenotype cause acute rejection of marrow grafts.

Acute rejection of allogeneic and semiallogeneic marrow grafts has long been considered to be a function of the natural immune system because it shares many features with NK activity in mice. With the use of a recently developed in vivo adoptive transfer assay in which spleen cells are transferred from mice able to reject a particular marrow graft into mice that fail to do so, we show that the cells responsible for induction of marrow graft rejection indeed display the phenotype of NK cells: they lack the T cell Ag CD4 and CD8 but express the NK Ag NK1 and ASGM1. The rejection induced by adoptively transferred cells is exquisitely specific--a feature that points to a specific recognition process by the transferred cells. To elucidate what the recognition structure on these cells may be we found that they express CD3 and most likely the beta-chain of the TCR. Highly purified responder cells with the NK1+, CD3+, CD4-, CD8- phenotype, when transferred into nonresponder recipients, cause specific marrow graft rejection. We conclude that the acute rejection of bone marrow grafts is caused by a cell that expresses NK phenotype but is of T cell lineage. This may suggest the specificity of acute marrow graft rejection is caused by a specific recognition process that involves TCR.

Effector cell expression of NK1.1, a murine natural killer cell-specific molecule, and ability of mice to reject bone marrow allografts.

The rejection of Hh-1 incompatible bone marrow cells in irradiated mice is mediated by NK cells and is genetically regulated. We tested the role of the NK-specific gene, NK1.1, in regulating the rejection of allogeneic bone marrow cell grafts. NK1.1+ mice, that are known to display strong resistance against Hh-1 incompatible grafts, were crossed to H-2/Hh-1 identical NK1.1-, poor responder mice, and the progeny were backcrossed to the poor responder parent. The segregating mice were individually typed for their expression of NK1.1 and the ability to resist Hh-1 incompatible bone marrow cells (BMC). A strong correlation was noted between expression of NK1.1 and rejection of H-2d/Hh-1d BMC. Our results support the idea that NK1.1 is one of the genes responsible for strong resistance to Hh-1d (determinant 2) but not for Hh-1j (determinant 3) BMC grafts. We suggest that the NK1.1 molecule functions as an accessory molecule in the cellular interactions involving the recognition of Hh-1 determinants.

CD4 monoclonal antibody pairs for immunosuppression and tolerance induction

A pair of rat anti-mouse CD4 monoclonal antibodies (mAb) have been selected which bind to different epitopes of the molecule. Both the mAb are rat IgG2b and show clear synergistic activity in complement lysis in vitro. When injected together in vivo, they exhibit an improved immunosuppressive effect, compared to each antibody alone, on allogeneic graft rejection, humoral responses and on tolerance induction. Limiting dilution analysis indicates that the in vivo depletion of interleukin 2-producing cells is improved using both mAb by 2-3-fold over that obtained with the individual antibodies. As little as 60 ng per mouse of the CD4 antibody pair was sufficient to allow the induction of tolerance to human gamma-globulin, even without elimination of the CD4+ cells. The results suggest that appropriate antibody pairs may be good candidates for effective immunosuppressive serotherapy in man.

T killer cells play a role in allogeneic bone marrow graft rejection but not in hybrid resistance.

Results of recent experiments have provided compelling evidence supporting the hypothesis that the acute rejection of bone marrow transplants by allogeneic and semiallogeneic recipients is principally due to the action of natural killer (NK) cells. The observed specificity of graft rejection is likely induced by target-specific antibody that guides the NK cells in an antibody-dependent cytolytic reaction resulting in the elimination of the graft. The sole involvement of NK cells in marrow graft rejection, however, is contradicted by several observations that point to the environment of specific T cells. Results presented in this paper demonstrate that in allogeneic marrow graft rejection models, T killer cells are capable of causing graft rejection provided a prior sensitization phase is allowed. Thus, mice not able to reject marrow grafts in a primary response via their NK cells will do so in a primed secondary response via their T cells. Rejection is specific in that only marrow grafts H-2 identical to the sensitizing marrow graft are rejected. Sensitization for NK cell independent marrow graft rejection can be accomplished by prior priming with allogeneic tumor cells or by injection of cloned T killer cells. In contrast to bone marrow allograft rejection, the hybrid resistance model in which F1 hybrid mice reject parental marrow grafts does not appear to induce T killer cells in vivo. Neither marrow grafts nor tumor cells prime F1 hybrids for a second-set parental graft rejection. Moreover, F1 hybrid antiparental T killer cells induced in vitro and adoptively transferred in vivo fail to transfer hybrid resistance. Therefore, there appear to be potent mechanisms acting in vivo that suppress the action or induction of F1 hybrid T killer cells specific to parental antigens.

Millipore diffusion chambers allow dissociation of myelin phagocytosis by non-resident cells and of allogenic nerve graft rejection

Allogenic graft rejection leads to rapid tissue destruction of nerves transplanted directly into a muscle lodge. If the nerves are enclosed in 5.0μm pore chambers and transplanted into the peritoneal cavity, there is no allogenic graft rejection. The phagocytosis of myelin by invading cells is, however, not disturbed, showing that these cells can distinguish the degenerating myelin from the Schwann cell without being responsive to the Schwann cell's allotype. If the allografts are allowed to predegenerate for 4 wk in 0.22 μm pore chambers which do not admit any cells, there is a striking mitigation of the allogenic graft rejection if the nerves are subsequently released from the chamber. Myelin phagocytosis in such nerves is also reduced. These observations indicate the existence of a hierarchy of cellular recognition mechanisms involved in nerve tissue degradation. Phagocytosis of the myelin sheath by macrophages involves recognition mechanisms which differ from those of the allogenic rejection of the Schwann cell, presumably mediated by T lymphocytes.

Pancreatic islet transplantation: immuno-alteration with ultraviolet irradiation.

AbstractTo circumvent rejection of allogeneic pancreatic islet grafts, we have examined the use of ultraviolet (UV) irradiation to inactivate allostimulatory cells in blood prior to their use for the induction of donor‐specific tolerance and to decrease the immunogenicity of pancreatic islets by direct UV irradiation. UVB (280–320 nm) irradiation of blood can effectively abrogate lymphocyte stimulatory capacity in an MLC, while subsequent transfusions of appropriately UV irradiated blood have indefinitely prolonged islet allograft survival in the Lewis to ACI rat strain combination (greater than 250 days), without the use of immunosuppressive agents. This treatment is donor specific in that third‐party W/F islet allograft survival is not prolonged in ACI rats transfused with UV‐treated Lewis blood (MST, 7.5 days). When W/F rats are used as donors of blood, moderate prolongation of W/F islet allograft survival is obtained (MST of 21±12 days). When non‐UV‐treated W/F blood is transfused, rejection of W/F islets is accelerated (MST of 2 days versus no treatment control of 6.5 days) in the ACI recipient.UV irradiation of rat dendritic cells can completely abrogate their powerful stimulatory activity in an MLC at a dose of 900 J/m2. Rat islets subjected to this same dose of UV irradiation do not exhibit any alteration in their endocrine function when transplanted into syngeneic diabetic animals. UV irradiated (900 J/m2) Lewis islets transplanted into non‐immunosuppressed ACI rats showed marked prolongation of survival (greater than 80 days).We conclude that UV irradiation is effective in immuno‐alteration of the stimulatory cells in blood and can selectively decrease immunogenicity of pancreatic islets without being deleterious to their endocrine function. Both these methods are readily applicable to islet transplantation in other animals and eventually in humans.