Cellular mechanisms: Induction of heart allograft survival in rats by 15-deoxyspergualin

Survival of ACI rat heart grafts in Lewis rat (LEW) recipients treated with a short course of 15-deoxyspergualin (DSG), in a dose of 5 mg/kg daily beginning from day 4 of grafting, was markedly prolonged, with a mean survival time of 29.8 ± 3.0 days. On day 20 after grafting, the cellular mechanism of inducing allograft survival after DSG treatment was analyzed by testing the activation of spleen cells in several assay systems. The results indicate that spleen cells from DSG-treated rats with surviving heart allografts show almost no proliferative response against donor strain stimulator cells in the mixed lymphocyte reaction (MLR) as compared with controls. Their cytotoxic activity was lower than that of spleen cells from rats with heart allograft rejection towards donor strain target cells. Adding various concentrations of spleen cells from DSG-treated LEW rats with surviving ACI heart allografts to the MLR when the responder cells from normal LEW rats were exposed to irradiated ACI or Wistar (third party) stimulator cells revealed a strong suppression, in a cell-dose-dependent manner. Moreover, the transfer of 2.0 × 10⁸ spleen cells from DSG-treated LEW rats with surviving ACI heart allografts to an irradiated grafted host did not prolong the survival either of the ACI heart grafts or of the third party Wistar heart grafts. These results suggest that the proliferative response and cytotoxic activity are lowered and suppressor cells are induced by treatment with DSG, in rats with surviving allografts.     

Sensitization interval and administration method alter the effect of 15-deoxyspergualin on heart transplantation in sensitized recipient rats

We evaluated the effect of 15-deoxyspergualin (DSG) on accelerated rejection. Brown Norway rats (BN) served as organ donors and Lewis rats (LEW) as recipients. In an accelerated rejection model, after a LEW rat was sensitized with BN skin, a BN heart was transplanted. Various intervals between sensitization and heart transplantation were examined. The heart allografts in sensitized recipients were rejected earlier than those in unmodified recipients regardless of the sensitization interval. DSG (2.5 mg/kg per day), given to the recipients during the sensitization phase, significantly prolonged graft survival compared with the untreated hosts when the sensitization interval was short. When the recipients were treated with DSG after heart transplantation, heart graft survival was significantly prolonged regardless of the sensitization interval. Flow cytometric analysis and complement-dependent cytotoxicity tests revealed that DSG suppressed antidonor antibody formation and that postoperative administration of DSG significantly decreased the proliferation of B cells when the sensitization interval was short and the proliferation of class II antigen-positive cells when the sensitization interval was long.     

Synergistic effect of donor-specific blood transfusion and a short course of deoxyspergualin in rat kidney transplantation

Deoxyspergualin (DSG), an analogue of spergualin produced by B. laterosporus, has a strong immunosuppressive effect in various transplantation models. We have investigated the mechanism of donor-specific prolongation of survival time in rat kidney grafting by donor-specific blood transfusion (DST) and a short course of DSG. Lewis (LEW) kidney allografts were transplanted into fully allogeneic BN rats. Fresh, whole LEW blood 1.0 ml, was injected i.v. into BN rats 2 days prior to transplantation. Then, DSG, 6 mg/kg per day, was administered by i.m. injection on days 0, 1, and 2 after transplantation. The recipients were divided into five groups: group 1 (n=6) no treatment: group 2 (n=6) DST only; group 3 (n=7) DSG only; group 4 (n=7) DST and DSG; and group 5 (n=6), third party (ACI rats) blood transfusion and DSG. Lymphocytes (cervical lymph nodes) and serum were harvested from BN recipients on day 7 postgrafting. For suppressor cell assays, lymphocytes from BN recipients in each group were added as a third cell to the mixed lymphocyte reaction (MLC) between nontransplanted BN lymphocytes (responder) and LEW or other third party (PVGC, ACI, WKA rats) lymphocytes (stimulator). Antidonor lymphocytotoxic antibody (ADLA) was checked by microcytotoxicity assays. Median survival times (MST) for each group were: group 1, 10 days; group 1, 10 days; group 3, 13 days; group 4, 75 days; and group 5, 13 days. Remarkable prolongation of MST was only noted in group 4. In the suppressor cell assay, group 4 showed significant suppression (40%; P<0.05); the other groups did not show any suppression. This suppressive activity in group 4 was effective only during the MLC between BN and LEW, not during the MLC of third party-BN combinations. Thus, suppressor cells from DST/DSG-treated BN recipients appear to be donor-specific. In the microcytotoxicity assay, the only group that showed any ADLA was group 2, which was not treated with DSG. These results clearly show that both induction of donor-specific suppressor cells and inhibition of ADLA production are associated with the remarkable donor-specific prolongation of kidney allograft survival in DST/DSG-treated recipients.     

Heart and spleen twin grafts in rats

The technical details of a new procedure for the simultaneous transplantation of the spleen and the heart in rats are described. One hundred sixtyfour such twin grafts from LEW to ACI rats and vice versa were performed. Seventeen animals were followed postoperatively without additional immunologic manipulations. There is a definite change in rejection pattern in terms of timing as well as intensity when heart and spleen twin grafts are compared with single cardiac grafts. A delay and mild form of rejection of twin grafts were observed especially in the strain combination of LEW to ACI. No graft-versus-host reaction occurred. There was no perfect correlation of the cardiac and splenic allografts in regard to their survival time. When the cardiac allograft arrested, however, the spleen was found to be rejected as well in all cases. In three cases a selective survival of the heart over the spleen was observed. Thus, the cardiac allograft can be used as a simple but not completely reliable indicator of the functional state of both grafts.     

Effect of FK-506 on heart allograft survival in the highly sensitized recipient rats as compared with ciclosporin and 15-deoxyspergualin.

The effect of FK-506 on allograft survival in unsensitized recipients has been established in several animal experimental models. In this present study, we investigated the immunosuppressive capacity of FK-506, in comparison with ciclosporin (Cs) and 15-deoxyspergualin (DSG), on heart allograft in presensitized rats. Heart grafts from male ACI rats were heterotopically transplanted to male LEW rats. All recipient rats were sensitized with donor-type whole blood admixed with immunoadjuvant (adjuvant complete Freund) 7 days prior to transplantation. FK-506, Cs and DSG were administered from day 0 to day 14 posttransplantation. The results showed that both FK-506 and Cs significantly prolonged heart allograft survival of presensitized recipients in a dose-dependent manner. The minimum effective dose in the treatment was less for FK-506 than for Cs. However, DSG showed almost no effect of prolongation in this experiment.     

Immunological Analysis of Rat Renal Transplant Recipients Exhibiting Long-term Survival Following Treatment with 15-Deoxyspergualin in the Early Postoperative Phase

Background : We previously reported that short-term administration of 15-deoxyspergualin (DSG), 5 mg/kg/day on postoperative days 4 through 7, prolonged survival of rat renal allografts indefinitely. We now report the immunologic environment of DSG-treated recipients in the early postoperative phase.
Methods : TO (RT1^u) rat kidneys were transplanted into WKAH (RT1^k) rats. Peripheral blood lymphocytes (PBL), splenocytes (SPC) and graft infiltrating lymphocytes (GIL) were harvested from rejecting (untreated) recipients on day 7 (group AR) and from DSG-treated recipients on days 7 (Group DSG7) and 14 (group DSG14). Flow cytometric analysis was done to determine characteristics of these cells. Mixed lymphocyte culture reactions (MLRs) were also studied to examine suppressive activities of sera, SPC, and GIL of each group by adding them to TO/WKAH MLRs.
Results : In all groups, the proportions of CD8-and interleukin2 receptor (IL-2R)-positive cells were higher for GIL than for either PBL or SPC. The CD4/CD8 ratio was lowest in GIL. Comparing groups DSG7 and DSG14, significant decreases in the proportion of CD8- and IL-2R-positive cells were found only in GIL. Sera of all groups nonspecifically suppressed MLRs, independent of DSG-administration. GIL of all groups also nonspecifically suppressed MLRs, while these suppressive activities were not observed with SPC. Suppressive activities of GIL remained unchanged in the first 2 postoperative weeks.
Conclusions : Differences in the immunologic environment were reflected primarily in GIL. DSG seemed to decrease CD8- and IL-2R-positive cells in allografts. In the presence of DSG, this model may feature a predominance of nonspecific suppressor T cells over cytotoxic T cells during the first 2 postoperative weeks.     

Control of humoral and cellular immunity-mediated accelerated heart allograft rejection in sensitized rats by low dose FK 506 and splenectomy

ACI heart grafts are rejected, at an accelerated pace, in Lewis (LEW) rats sensitized by donor-type blood admixed with immunoadjuvant (adjuvant complete Freund, ACF) 7 days earlier. In an in vitro study, the anti-ACI cytotoxic antibody titers in the serum increased from 1:4 in nonsensitized rats to 1:128 in sensitized rats; the spontaneous blastogenesis in spleen cells was higher in sensitized rats than in nonsensitized rats; spleen cells from sensitized rats showed a strong proliferative response against donor strain stimulator cells compared with the control; the cytotoxic T cell activity of spleen cells from sensitized rats was higher than that of spleen cells from nonsensitized rats. Treatment with low dose FK 506 in combination with splenectomy (Spx) synergistically prolonged the heart allograft survival in this sensitized rat model. In conclusion: (1) Both humoral and cellular responses against the donor antigen appear in the serum and in the spleen of rats sensitized by donor-type blood admixed with immunoadjuvant ACF. (2) A low dose of FK506 together with Spx appears to control this sensitization through different mechanisms, resulting in a prolongation of heart allograft survival.     

Influence of 15-deoxyspergualin on activated lymphocytes: Comparison of heart and renal rat transplantation models

Background. Among the immunological effects of 15-deoxyspergualin (DSG), its action on activated T lymphocytes with the interleukin 2 receptor (IL-2R) is controversial. Materials and methods. To investigate this action, we used rat heart and rat renal transplantation models in which Brown Norway rats (BN) served as the organ donors and Lewis rats (LEW) as the organ recipients. DSG was administered intraperitoneally to the recipients immediately after the operation. The percentage of IL-2R-positive cells and of CD4- and CD8-positive cells in the recipient spleen or allograft was evaluated. Results. The average survival period (days) of the BN heart or renal allograft in hosts treated with DSG was significantly longer than that in the untreated hosts. In the heart transplantation model, DSG decreased the percentage of IL-2R-positive cells and increased the CD4/CD8 ratio in the allograft. By contrast, in the renal transplantation model, DSG suppressed the percentage of IL-2R-positive cells in the spleen,but influenced neither the percentage of IL-2R-positive cells nor the CD4/CD8 ratio in the allograft. Conclusion. DSG extended allograft survival significantly in both heart and renal transplantation models. However, the influence of DSG on IL-2R-positive cells may be different in the two types of allografts. Received: March 30, 1998 / Accepted: September 2, 1998     

Suppression of liver allograft rejection by administration of 15-deoxyspergualin

In this experiment, the effect of the administration route-the hepatic artery, portal vein, or systemic circulation-of the immunosuppressive drug 15-deoxyspergualin (DSG) on the suppression of liver allograft rejection is investigated. A 3-day injection of DSG at a dose of 0.32–1.28 mg/kg per day into the systemic circulation of a rat that had received a liver transplant was not effective in prolonging liver graft survival (14.3±2.9 days vs. 14.1±2.5 days for controls). However, the administration of DSG into the portal vein following liver transplantation markedly prolonged survival for up to 24.9±10.0 days. Survival times were prolonged even more when the DSG was administered via the hepatic artery for 3 successive days after liver grafting (30.9±9.6 days). The concentration of DSG in the blood following the one-shot injection of DSG was highest when DSG was administered via the hepatic artery, intermediate when injected into the portal vein, and lowest when injected into the systemic vein. In conclusion, DSG can inhibit liver graft rejection more effectively via the hepatic arterial route than via the portal vein or systemic circulation.     

The role of class I major histocompatibility complex antigens in prolonging the survival of hepatic allografts in the rat

In an attempt to study the role of class I major histocompatibility complex antigens in inducing immunological unresponsiveness, the survival rates of hepatic allografts were compared in rats pretreated with blood taken from various rat strains. A single intravenous injection of 1 ml fresh heparinized whole blood seven days before transplantation significantly prolonged the survival of subsequent donor-specific hepatic allografts in the fully allogeneic ACI(RT1a)-to-LEW(RT1l) rat combination. However, pretreatment with blood taken from the third-party strain BN(RT1n) did not produce suppression of rejection, attesting to the specificity of the pretransplant transfusion effect. Interestingly, pretransplant transfusion of PVG.r1 blood, sharing only the RT1.A MHC region with ACI, significantly prolonged the survival of ACI-to-LEW hepatic allografts. In addition, no lymphocytotoxic antibodies could be detected at 30 or 100 days after transplantation in animals with long-surviving hepatic allografts pretreated with either PVG.r1 or ACI whole blood. On the other hand, pretreatment with PVG(RT1c) blood increased the survival of ACI-to-LEW hepatic allografts only moderately compared with controls. This finding may be consistent with a partial effect of some third-party blood transfusion. The experimental data suggest that the class I MHC antigens can be immunosuppressive in rat hepatic allografts. Adoptive transfer of 5 x 10(7) splenocytes taken from long-term-surviving hepatic allografts pretreated with donor ACI whole blood or PVG.r1 blood into irradiated (750 rads) LEW rats prolonged the survival of donor-type skin grafts, whereas third-party strain (BN) grafts were rejected. This finding suggests the presence of donor-specific suppressor cells.     

Induction of tolerance to hind limb allografts in rats receiving cyclosporine A and antilymphocyte serum: effect of duration of the treatment

BACKGROUND: This study assessed the ability of antilymphocyte serum (ALS) and cyclosporine A (CsA) to induce tolerance for hind limb composite tissue allograft in rats without chronic immunosuppression. METHODS: Hind limb transplantations were performed in Lewis-Brown-Norway (LBN, RT1(1+n)) and Lewis (LEW, RT1(1)) rats. Treatment consisted of ALS only (0.4 mL/kg), CsA only (16 mg/kg), and a combination of CsA and ALS, and it was administered 12 hr before surgery at three different intervals (7, 14, and 21 days). Long-term survivors were tested for tolerance by standard skin grafting from the recipient (LEW), the donor (LBN), and the third party (ACI, RT1 ) 60 days after cessation of the treatment and by mixed lymphocyte reaction at 100 days. T-cell lines were analyzed with flow cytometry. RESULTS: Single use of ALS in all treatment intervals did not prolong allograft survival. Single use of CsA extended survival up to 23 days in the 21-day protocol group. CsA and ALS caused indefinite survival in two of six rats in the 14-day protocol and in all six rats in the 21-day protocol (>420 days). The six long-term survivors in the 21-day protocol accepted the skin grafts from the donor (LBN) and the recipient (LEW) and rejected third-party grafts (ACI). Tolerant animals showed a donor-specific hematopoietic chimerism of 35% to 42% in the peripheral blood. Mixed lymphocyte reaction assay demonstrated tolerance to the host and donor alloantigens and increased response to the third party. CONCLUSIONS: Administration of CsA and ALS for 21 days induced donor-specific tolerance in the recipients of the rat hind limb composite tissue allografts. The mechanism of tolerance should be investigated further.     

Down-regulation of the immune response to histocompatibility antigens and prevention of sensitization by skin allografts by orally administered alloantigen.

The effects of oral administration of major histocompatibility antigens on the alloimmune response have not been investigated. Lymphocytes from inbred LEW (RT1u) rats that were pre-fed allogeneic WF (RT1l) splenocytes exhibited significant antigen specific reduction of the mixed lymphocyte response in vitro and delayed-type hypersensitivity response in vivo, when compared with unfed controls. In an accelerated allograft rejection model, LEW rats were presensitized with BN (RT1n) skin allografts 7 days before challenging them with (LEW x BN)F1 or BN vascularized cardiac allografts. While sensitized control animals hyperacutely reject their cardiac allografts within 2 days, animals prefed with BN splenocytes maintained cardiac allograft survival to 7 days, a time similar to that observed in unsensitized control recipients. This phenomenon was antigen-specific, as third-party WF grafts were rejected within 2 days. Immunohistologic examination of cardiac allografts harvested on day 2 from the fed animals had markedly reduced deposition of IgG, IgM, C3, and fibrin. In addition, there were significantly fewer cellular infiltrates of total white blood cells, neutrophils, macrophages, T cells, IL-2 receptor-positive T cells, and mononuclear cells with positive staining for the activation cytokines IL-2 and IFN-g. On day 6 posttransplant, the grafts from fed animals showed immunohistologic changes typical of acute cellular rejection usually seen in unsensitized rejecting controls. Feeding allogeneic splenocytes prevents sensitization by skin grafts and transforms accelerated rejection of vascularized cardiac allografts to an acute form typical of unsensitized recipients. Oral administration of alloantigen provides a novel approach to down-regulate the specific systemic alloimmune response against histocompatibility antigens.     

Intragraft delivery of 16, 16-dimethyl PGE2 induces donor-specific tolerance in rat cardiac allograft recipients

The stable prostaglandin E2 analogue, 16,16-dimethyl PGE2 (di-M-PGE2) was continuously infused by osmotic pump directly into rat heterotopic cardiac allografts. Intragraft delivery of 20 micrograms/kg/day di-M-PGE2 for 2 weeks completely prevented graft rejection for more than 150 days (n = 10), while untreated Buffalo recipients rejected Lewis cardiac allografts within 8 days after transplantation (mean survival time = 7.4 +/- 0.5 days, n = 5). When given for only 1 week, 20 micrograms/kg/day had a partial effect, since 60% of recipients accepted grafts long-term and 40% experienced rejection by day 14 (n = 5). In contrast, systemic intravenous administration of 20 micrograms/kg/day di-M-PGE2 for 2 weeks could not prolong graft survival (MST = 7.0 +/- 0.0 days, n = 3), and the higher dose of 200 micrograms/kg/day resulted in death by day 2 (n = 5). Long-term BUF recipients of LEW cardiac allografts accepted LEW donor strain skin grafts for more than 35 days while rejecting third-party Wistar Furth skin grafts in a normal fashion (MST = 7.3 +/- 0.5 days, n = 3), indicating the induction of donor-specific tolerance. Long-surviving LEW cardiac allografts retransplanted into naive BUF recipients were rejected within 7 days (MST = 6.7 +/- 0.5 days, n = 3), indicating no change in graft immunogenicity. Therefore, a 14-day infusion of di-M-PGE2 directly into a strongly MHC-mismatched cardiac allograft uniformly has resulted in long-term engraftment and the development of recipient donor-specific tolerance.     

Liver allografts are toleragenic in rats conditioned with posttransplant total lymphoid irradiation

BACKGROUND: Posttransplant total lymphoid irradiation (TLI) treatment has been applied to tolerance induction protocols in heart and kidney transplantation models. METHODS: We examined the efficacy and mechanism of posttransplant TLI treatment in the induction and maintenance of tolerance in a rat orthotopic liver transplantation model. RESULTS: Posttransplant TLI prolonged ACI (RT1(a)) liver allograft survival in Lewis (RT1(b)) hosts, with 50% long-term engraftment without immunosuppression and without evidence of chronic rejection. Injection of donor-type liver mononuclear cells (LMCs) facilitated the prolongation of graft survival, with more than 70% of grafts in LMC recipients surviving more than 100 days without chronic rejection. Recipients with long-term liver allograft survival accepted ACI but not PVG skin grafts. In TLI-conditioned recipients with accepted grafts, apoptosis occurred predominantly in graft-infiltrating leukocytes. In contrast, there were few apoptotic leukocytes in rejecting grafts. Recipients with long-term graft acceptance (>100 days of survival) demonstrated evidence of immune deviation; mixed lymphocyte reaction to ACI stimulator cells was vigorous, but secretion of interferon-gamma and interleukin-2 was reduced. In tolerant recipients, the number of Foxp3(+) CD25(+) CD4(+) regulatory T cells was increased in the liver allograft as well as in the peripheral blood. CONCLUSION: We conclude that posttransplant TLI induces tolerance to liver allografts via a mechanism involving apoptotic cell-deletion and immunoregulation.     

Intestinal allograft survival in the rat following pretreatment with donor-specific UV-B-irradiated leukocytes and peritransplant immunosuppression with cyclosporine

Previous studies from our laboratory showed that pretreatment with ultraviolet-B-irradiated donor leukocytes (UV-B DL) combined with brief peritransplant cyclosporine (CyA) resulted in indefinite survival of Wistar/Furth rat cardiac allografts in Lewis recipients. This study was designed to examine the effect of pretransplant UV-B DL with or without peritransplant CyA on orthotopic intestinal allografts in the same rat strain combination. The results showed that while low-dose CyA treatment alone (10 mg/kg i.m. on days 0, +1, and +2) had no effect on intestinal allograft rejection, 20 mg/kg (on days 0, +1, and +2) CyA significantly (P0.001) prolonged graft survival, with 33% of the hosts surviving indenfinitely. The highest dose of CyA (30 mg on days 0, +1, and +2) abrogated rejection, but most transplant recipients succumbed to infection and functional ileus due to a toxic side effect of CyA. Pretreatment with UV-B DL on days -14 and-7 alone did not prolong intestinal allograft survival. Combination of a subtherapeutic CyA dose (20 or 10 mg/kg) given on days 0, +1, and +2 with pretransplant UV-B DL on days-14 and -7 did not alter the survival of intestinal allografts compared to treatment with CyA alone. This suggests that pretreatment with UV-B DL with or without peritransplant administration of CyA has no effect on intestinal allograft survival, in contrast to the effect of such combined treatment on cardiac allograft survival, where indefinite graft survival is observed. This difference in the effect of pretransplant UV-B DL on intestinal and cardiac allograft survival is most likely due to organ-specific immunogenicity, particularly to the relative density of class I and II histocompatibility antigens present in heart or intestine.     

Long-term survival of cardiac allografts in lethally irradiated rats repopulated with host-type hemopoietic cells.

To test the hypothesis that hemopoietic cells within a tissue graft are responsible for its immunogenicity, two experimental protocols were followed. LEW hearts were grafted into (LEW X BN)F-1 host rats and LEW or F-1 lymphocytes were injected into the apex of the grafted heart. The LEW but not the F-1 cells induced a local reaction, apparently because the circulating F-1 cells were the necessary immunogens. The second protocol took advantage of the knowledge that lethally irradiated LEW rats were able to reject WF Ag-B-incompatible hemopoietic cells (but not tissue allografts) within a few days. LEW rats were lethally irradiated and grafted with WF hearts on day 0. A mixture of LEW marrow, thymus, spleen and lymph node cells, or marrow cells only were infused either on day 0 or day 2. Cardiac allografts in hosts repopulated with the mixture of lymphoid cells survived a mean of 11.3 days in hosts infused on day 0, but survived indefinitely if the lymphoid cells were infused on day 2. The 2-day interval also prolonged the survival of allografts in rats infused with only marrow cells. The long-term recipients, without any further treatment, rejected WF skin grafts as first-set reactions 1 year later but did not reject second WF cardiac allografts. Lymphoid cells from long-term recipients imparied the rejection of WF cardiac allografts by LEW host rats. The lack of rejection of the original cardiac allograft supported the hypothesis tested. Certain hemopoietic cells responsible for the immunogenicity of cardiac allografts were probably eliminated in the 2-day interval at least in part by host effector cells capable of rejecting allogeneic hemopoietic cells. However, the mechanism of long-term "unresponsiveness" to WF hearts could have been caused by loss of accessory cells during the 2-day interval followed by infusion of immunocompetent cells. Skin rejections in these recipients may have been attributable to reactions against skin differentiation-specific antigens.     

Immunological unresponsiveness to hepatic allografts in rats. Immunological reactivities of the recipient to donor antigens

Wistar (RT1bv1) rats transplanted orthotopically with ACI (RT1a) livers survive indefinitely without any immunosuppression, while heterotopic heart grafts or skin grafts are rejected acutely in this combination. Levels of alkaline phosphatase after liver allografting remain significantly higher than those found in controls receiving syngeneic grafts. We studied changes in immune responsiveness in rats receiving liver grafts. Local graft-versus-host reactivity was present at all times assayed. Delayed type hypersensitivity reactions were already positive 2 weeks after liver transplantation and increased in strength. Liver graft-bearing rats were subsequently grafted with donor or third-party skin. Third-party skin grafts survived significantly longer on liver-grafted rats than on untreated controls when grafted within the first week after grafting. Donor-type skin grafts survived longer than controls when grafted within the first 4 weeks after liver grafting, although the skin grafts were eventually rejected. Donor-type skin grafted more than 8 weeks after liver grafting was rejected acutely. In an adoptive transfer assay, ACI hearts survived significantly longer in Wistar rats given serum from Wistar donors 2-4 weeks after ACI liver grafts than in untreated controls. On the other hand, spleen cells obtained at any period after liver grafting were not capable of prolonging cardiac allograft survival after transfer to syngeneic recipients. Thus cellular responses to ACI antigen are not changed during the life-span of liver-grafted animals. Evidence suggests that a serum "enhancing" factor protects the donor liver from rejection in the initial period after liver transplantation. The long-term acceptance of liver grafts is discussed.     

Effect of cyclosporin therapy in controlling the rejection of ileal versus jejunal allografts

Experimental evidence suggests that jejunal allografts are rejected as rapidly as are ileal grafts, despite their lesser content of lymphoid tissue as an immunologic stimulus. However, it may be possible to postpone the rejection of jejunal grafts more readily than that of ileal grafts by means of immunosuppressive therapy with cyclosporin (CyA). To test this, we used the rat model (BN-LEW) of orthotopic small-bowel transplantation. The proximal third of the small-bowel with one-third of the mesenteric lymph nodes (n=20), or the distal ileal third with all of the mesenteric lymph nodes (n=22), or the entire small-bowel (n=23) was interposed after resection of an equivalent type and length of recipient bowel. CyA (15 mg/kg) was given to all of these rats for 5 days. Three additional control groups were not given CyA. The difference in graft/recipient survival among the groups receiving CyA and among those not on CyA therapy was not statistically significant. Antidonor hemagglutinin titers, the mixed lymphocyte culture (MLC) assay, and histologic examination of the allograft failed to show a mitigated rejection reaction for the recipients of jejunal grafts. The data show that short-term treatment with CyA prolongs graft survival. Equal doses of CyA, however, did not lead to prolonged survival of jejunal grafts or alter the course of rejection in comparison with that for ileal or whole-bowel transplants.Presented at the 1988 Tripartite Meeting of the Society of University Surgeons (SUS), the Surgical Research Society of Great Britain (SRS), and the European Society for Surgical Research (ESSR) Bristol, UK     

The role of T suppressor cells in the maintenance of spontaneously accepted orthotopic rat liver allografts.

Orthotopic liver allografts from BN donors to LEW recipients are spontaneously accepted, and the recipients develop donor-specific immunological unresponsiveness. This unresponsiveness may be mediated by suppressor T cells. Immunomagnetically purified splenic T cells from LEW rats bearing BN liver grafts were shown to adoptively transfer suppression of skin, heart, and kidney graft rejection in a donor-specific manner, prolonging the survival of BN but not third-party DA grafts. However, the suppressor T cells were sessile, being resident in the spleen but not present in thoracic duct lymph. The presence of a nonrecirculating suppressor T cell in rats spontaneously accepting liver transplants is strongly suggestive of an important function in the maintenance of donor-specific unresponsiveness, although the contribution of other possible mechanisms of unresponsiveness has not been investigated.     

Studies of the induction and maintenance of long-term graft acceptance by treatment with FK506 in heterotopic cardiac allotransplantation in rats

Immunosuppressive activities of the newly discovered FK506, isolated from Streptomyces tsukubaensis, were examined by using cardiac allotransplantation in the rat, and the mechanisms underlying induction and maintenance of FK506-induced long-term allograft survival were studied. Male rats of WKA (RT1k) and F344 (RT1lvl) strains were used as recipients and donors, respectively, and those of BN (RT1n) strain were used as third-party donors. Treatment with FK506, beginning from the day of allografting for 14, 10, or as few as 4 days, prolonged allograft survival significantly across the major histocompatibility barrier. The minimum doses for prolonging graft survival were 0.1 mg/kg/day by intramuscular treatment and 1.0 mg/kg/day by oral treatment. Treatment with FK506 at a dose of 0.32 mg/kg/day from day 4 until day 10 resulted in all the grafts surviving indefinitely and from days 5 to 10, half the grafts survived indefinitely, suggesting that the agent inhibited ongoing rejection. On the other hand, cyclosporine treatment at a dose of 20 mg/kg/day from day 2 did not prolong graft survival time statistically significantly. Induction of prolonged graft survival was not obtained by pretreatment of the prospective donor or recipient; prolonging effects were observed only when the agent was administered after allografting. Thus, the primary effect of the agent is exerted on responder lymphocytes reacting to the donor antigens in the induction phase of long-term graft acceptance. The mechanisms underlying the maintenance of long-term grafts were analyzed by testing the capacity of lymphocytes or serum of long-term graft-bearing rats to inhibit graft rejection in irradiated grafted hosts. Transfer of 2 x 10(8) lymphocytes from FK506-induced long-term F344 graft-bearing WKA rats resulted in indefinite survival of F344 heart allografts, but it did not prolong survival of third-party BN hearts. Transfer of 2.5 ml serum from long-term graft-bearing rats also prolonged graft survival of F344 hearts, but not BN hearts. These results suggest that donor strain-specific suppressor cells and humoral factor(s) are induced by treatment with FK506 in the presence of allografts, and that they play at least partial roles in the maintenance of long-term allograft acceptance.