Immunosuppression and rejection of cartilage formed by allogeneic chondrocytes in rats

Rat syngeneic and allogeneic chondrocytes were transplanted intramuscularly or into defects prepared in articular cartilage (intracartilaginous transplants). Recipients of allogeneic transplants received cyclosporin A (CsA), cladribine (2-chlorodeoxyadenosine, 2-CdA), or both drugs in combination. Transplants were taken for examination after 5 weeks. Cartilage formed intramuscularly by syngeneic chondrocytes was ossified. Allogeneic cartilage was resorbed by infiltrating cells. CsA or 2-CdA partially suppressed, and both these agents in combination strongly suppressed, formation of infiltrations. Both syngeneic and allogeneic chondrocytes formed cartilage in joint surface defects but only allogeneic cartilage was attacked by infiltrating cells. CsA + 2-CdA treatment slightly decreased intensity of infiltrations but did not prevent cartilage resorption. Antichondrocyte response was studied by evaluation of spleen mononuclear cells (SMC) stimulation in mixed splenocyte-chondrocyte cultures and by detection of antichondrocyte cytotoxic antibodies. SMC stimulation index (SI) was calculated separately for syngeneic and allogeneic chondrocytes. Comparison of SMC SI for syngeneic and allogeneic chondrocytes indicated lack of stimulation of SMC from control or syngeneic transplant recipients and significant stimulation of SMC from recipients of allogeneic transplants. SMC from animals treated with CsA + 2-CdA were not stimulated. Additional experiments aiming at an explanation of the lack of stimulation of SMC from intact animals by syngeneic chondrocytes reported in this work and contrary to other findings disclosed that it was caused by the use of collagenase solution containing N alpha-p-tosyl-l-lysine chloromethyl ketone for chondrocyte isolation. Spontaneous antichondrocyte cytotoxic antibody activity was found in intact rats raised only in sera from recipients of allogeneic intramuscular transplants without immunosuppression. Thus, strong immunosuppressive treatment of rats with allogeneic chondrocyte transplants was more effective in relation to the general immunological response than to the local reaction.     

Effect of immunosuppression on rejection of cartilage formed by transplanted allogeneic rib chondrocytes in mice

The effect of short-term immunosuppressive treatment with antithymocyte serum-procarbazine (ATS-PCH) and cyclosporin-A (Cy-A) on survival of allogeneic rib chondrocyte grafts was examined morphologically and by evaluation of specific humoral and cellular antigraft immunity. The latter were evaluated by means of leukoagglutination and the indirect migration inhibition assay, respectively. Untreated recipients of syngeneic rib chondrocytes and untreated recipients of whole syngeneic and allogeneic rib cartilage served as controls. Transplanted syngenic rib chondrocytes formed cartilaginous nodules similar to rib cartilage in situ. These nodules contained hypertrophied chondrocytes, but neither physiologic resorption by vascularized connective tissue nor bone formation occurred after an observation period of longer than six weeks. Transplantation of allogeneic chondrocytes resulted in development of humoral and cellular antigraft immunity, and the formed cartilage was destroyed by infiltrating immune cells. Immunosuppression by ATS-PCH resulted in inhibition of graft destruction and a marked decrease of specific humoral antigraft immunity. Cellular antigraft immunity did not occur. Moreover, neither the histologic appearance of the cartilaginous nodules nor the results of immunologic response evaluations in the ATS-PCH-treated group differed from those in untreated whole allogeneic cartilage recipients. Treatment with Cy-A did not significantly improve survival cartilage formed by allogeneic chondrocytes.     

Effect of immunosuppression on survival and growth of cartilage produced by transplanted allogeneic epiphyseal chondrocytes

Strong short-term immunosuppression improved survival of cartilage formed by transplanted allogeneic epiphyseal chondrocytes in mice. The agents tested were cortisone acetate (CA), cyclophosphamide (CY), procarbazine (PCH), and antithymocyte serum (ATS). Their effect on syngeneic grafts was examined morphologically and histomorphometrically. In untreated recipients, chondrocytes formed cartilage nodules that underwent endochondral ossification. Except for high repetitive doses of CY, none of the other agents interfered with normal cartilage formation. However, all agents affected endochondral ossification. In the allogeneic system, the effect of immunosuppression was examined morphologically and by evaluation of specific humoral and cellular antigraft immunity. Allogeneic chondrocytes evoked a strong immune response in untreated mice, and cartilage was gradually destroyed by infiltrating cells. Endochondral ossification did not occur in this system. Neither agent given alone exerted a marked, long-lasting protective effect upon the graft. However, combined treatment with ATS and PCH inhibited immune response and completely prevented infiltrate formation and allowed endochondral ossification similar to that in the syngeneic control. Although some weak signs of antigraft immunity were seen after six weeks, it is possible that they were due to secondary exposure of antigen-bearing chondrocytes in the course of endochondral ossification.     

Impact of MHC mismatch and freezing on bone graft incorporation: An experimental study in rats

Cortical bone graft failure develops for poorly defined reasons, and the effects of the immune responses on the incorporation of an allograft are less clear. In a rat model of tibial allotransplantation, we have studied biometric and histological changes of the graft and the humoral immune response against it. We have also compared fresh with prefrozen grafts to study putative effects of freezing on the healing of the graft and the immune response against it. Fresh and frozen cortical bone grafts matched or mismatched for major histocompatibility complex antigens (syngeneic and allogeneic grafts) were implanted in an 8‐mm segmental defect in the tibia. The construct was stabilized with intramedullary nailing. Incorporation of the graft was assessed with use of conventional radiography, micro computed tomography (CT(, biomechanical testing and histological examination. The immune response was evaluated by monitoring distribution of leukocytes in the blood and by measuring antibodies in a tailor‐made fluorescence activating cell scanning (FACS( analysis. We found that the fresh syngeneic grafts were well integrated after 8 weeks with intact bone cells. In the fresh allogeneic grafts, all cells were dead with radiological signs of resorption, and mechanical testing indicated failure of incorporation. The frozen grafts showed poorer overall reconstruction than the fresh syngeneic grafts, but the incorporation was better than the fresh allogeneic grafts. A measurable alloantibody response was only detected after fresh allografting. The combined results suggest that freezing of bone allograft impedes the antibody response against major histocompatibility complex (MHC( antigens and improves incorporation, but frozen allografts still perform poorer than do frozen syngeneic grafts. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:925–931, 2008     

The survival and nature of the immune response to soft-tissue and composite-tissue allografts in rats treated with low-dose cyclosporine

We studied a variety of soft-tissue and composite-tissue allografts (CTA) in a histoincompatible rat model to determine the outcome and the nature of the immunologic responses to these tissues using continuous low-dose cyclosporine (CsA) therapy. Brown-Norway (RT1n) rats served as donors of soft tissue and CTA to Lewis (RT1l) rat recipients given low-dose CsA immunosuppressive therapy by gavage. Nine groups were studied. Three control groups were not treated with CsA: group 1, skin grafts alone; group 2, skin flaps alone; and group 3, skin grafts and delayed vessel allotransplants. Six groups were treated with CsA: group 4, skin grafts alone; group 5, skin flaps alone; group 6, skin grafts and delayed vessel allotransplants; group 7, aortas alone; group 8, muscle flaps alone; and group 9, bone grafts alone. Isografts were performed in all groups as technical controls. The appearance posttransplant of donor-directed cytotoxic antibodies was determined in recipient serum using a complement-mediated cytotoxicity assay and was compared to control and pretransplant sera. In the absence of CsA therapy, recipients in groups 1, 2, and 3 rejected their allografts early (8.5-9.4 days) and developed profound antidonor cytotoxic antibody activity posttransplant by day 7. Groups 4, 5, 6, 7, and 9 had prolonged graft survival in the presence of low-dose CsA, despite the presence of antidonor antibody activity. By contrast, group 8 (muscle flaps) were all uniformly rejected in the presence of profound recipient cytotoxic antidonor antibody activity. These results suggest that long-term soft-tissue and CTA survival can be achieved in histoincompatible rat recipients using continuous low-dose CsA immunosuppressive therapy despite the presence of cytotoxic antidonor antibodies.     

Transplantation of isolated chondrocytes

Intramuscular transplantation of isolated syngeneic chondrocytes from hyaline and elastic cartilage results in formation of cartilage with various degrees of similarity to the original tissue. Cells from cartilage with a simple structure, such as nasal septal cartilage, form islands of tissue with flattened chondrocytes at the periphery and more rounded ones in the center. Chondrocytes from auricular (elastic) cartilage taken from young animals produce islands of tissue with an arrangement of cells and fibers similar to that of the material used for isolation of chondrocytes. Cartilage produced by elastic chondrocytes from older animals has an irregular arrangement of cells and contains fewer elastic fibers than cartilage produced by chondrocytes of corresponding age in situ. Chondrocytes from epiphyseal cartilage produce tissue with an irregular arrangement of cells, but nevertheless, are treated with endochondral ossification. Transplants of allogeneic chondrocytes evoke a strong immune response in the recipient. Such chondrocytes produce cartilage that is surrounded and slowly resorbed by infiltrating cells and does not ossify. Short-term immunosuppression (procarbazine and antithymocyte serum) prevents rejection of such cartilage and allows endochondral ossification.     

Induction of a suppressive serum factor, prevention of sensitization, and prolongation of kidney graft survival in rats by transfusion with antibody-coated blood cells

Transfusion with antibody-coated allogeneic blood cells suppresses the cytotoxic antidonor antibody response in a strongly incompatible rat combination (BN----LEW). Cell coating with homologous recipient antidonor antiserum, rat monoclonal antibodies against MHC class I donor antigens, or rabbit antirat lymphocyte serum all were effective. The suppression was not abrogated by repeated booster transfusions with untreated donor blood. Moreover, the suppression extended to antibody-uncoated antigens present on the same donor cell. Not only the antibody response but also the Graft-versus-host reaction against donor antigens was suppressed. The serum of pretreated animals contained suppressive activity. It suppressed the cytotoxic antibody response as well as the cellular immune response (GVH) when transferred into syngeneic recipients. A weaker suppression of antibody response was obtained by transferring spleen cells of pretreated animals into syngeneic recipients. The transfer data suggest that broadly reactive serum factor(s) were mainly responsible for the suppressive effect. Transfusion with LEW-anti-BN-coated donor cells before transplantation induced markedly prolonged kidney graft survival in the BN----LEW combination without additional immunosuppression (untreated controls: 8.4 +/- 0.4, pretreated recipients: 124 +/- 36 days, P less than 10(-4)).     

同种异体软骨细胞与自体骨髓基质干细胞混合共培养构建软骨皮下移植的可行性研究

背景：软骨组织工程的种子细胞问题是目前研究的热点和难点,如何找到一种既能够避免对自体软骨进行取材又能够达到稳定软骨构建目的的方法呢？本研究尝试利用少量同种异体羊软骨细胞作为软骨诱导微环境提供者,与扩增后的羊自体BMSC混合共培养并植入皮下环境,探讨利用同种异体软骨细胞共培养构建软骨皮下移植的可行性。方法：本实验对山羊软骨细胞和BMSC分别进行取材和分离培养扩增,并将以上细胞分为以下四组进行混合并接种在PGA支架材料上：A组：100%自体软骨细胞;B组：30%自体软骨细胞＋70%自体BMSCs;C组：30%同种异体软骨细胞＋70%自体BMSCs;D组：100%同种异体软骨细胞。经过体外构建6周后植入羊皮下进行体内构建12周,对所形成的组织块进行大体观察和组织学染色等评价。结果：自体软骨细胞组和自体软骨细胞混合自体BMSC组皮下移植后可见成熟软骨组织形成,但同种异体软骨细胞参与的两组（包括同种异体软骨细胞混合自体BMSC的实验组和单纯异体软骨细胞组）在皮下环境中都因为较强的免疫反应未能形成软骨组织。结论：同种异体软骨细胞以及PGA支架材料的存在对于组织工程软骨在羊皮下环境的构建有负面影响。     

Early increased chemokine expression and production in murine allogeneic skin grafts is mediated by natural killer cells

BACKGROUND: Increased expression of chemokine mRNA is observed in allogeneic but not syngeneic skin grafts 3-4 days after transplantation. The recipient cells mediating this early inflammatory response in allografts remain unidentified. METHODS: Isogeneic and allogeneic skin grafts were transplanted to euthymic and athymic nude mice. mRNA expression and protein production of macrophage inflammatory protein-1alpha (MIP-1alpha), MIP-1beta, and the murine homolog of Gro(alpha), i.e. KC, from graft homogenates retrieved 3-4 days posttransplantation was tested by Northern blot hybridization and ELISA. To deplete NK cells, recipients were treated with antiasialo GM1 (ASGM1) antisera or with anti-NK1.1 mAb before transplantation. RESULTS: Expression of KC, MIP-1alpha, and MIP-1beta mRNA was equivalent in C57BL/6 allogeneic skin grafts and BALB/c isografts at day 2 posttransplant. At day 3 posttransplant, chemokine mRNA levels decreased in isografts but were maintained at high levels in the allografts. Increased early chemokine mRNA was also observed in C57BL/6, but not BALB/c++ grafts on BALB/c athymi(nu/nu) recipients. Treatment of allograft recipients with ASGM1 or with anti-NK1.1 antibody eliminated NK cells from the spleen and allograft infiltrating cell populations and decreased early chemokine mRNA levels in allografts 60-70%. Analyses of allograft homogenates indicated increased levels of KC, MIP-1alpha, and MIP-1beta protein at day 4 posttransplant that were decreased in recipients depleted of NK cells. Early chemokine mRNA levels were equivalent in isogeneic and semiallogeneic F1 grafts. CONCLUSIONS: Early chemokine mRNA expression and protein production in allogeneic skin grafts is amplified by recipient natural killer (NK) cells. These results indicate a novel function for infiltrating NK cells in mediating early increased intra-allograft chemokine production and inflammation during the initiation of acute rejection.     

Suppression of antibody response and prolongation of skin graft survival by multiple blood transfusions in the rat

The effect of blood transfusions (BT) on antibody response and skin graft survival was studied in the strongly MHC-incompatible BN and LEW combination. One-to-three BT induced high titer antibodies. Additional BT, however, led to a decrease of antibody titers. After 15 BT the recipients either had no detectable antibodies, or they had very low antibody titers. This suppression of response was shown to be distinct from a simple loss of antibody activity caused by lack of further antigenic challenge. In multiple transfused rats, humoral nonreactivity persisted in spite of rechallenge with antigen; in animals that lost their antibodies as a result of lack of further stimulation, an additional BT boosted strong antibody production. In LEW recipients of multiple BN transfusions, not only the specific anti-BN response but also reactivity to third-party BUF blood was suppressed. However, whereas the donor-specific response (anti-BN) was largely inhibited after a ten-week interval, the response to third-party BUF blood recovered. The state of humoral nonreactivity could be transferred by spleen cells to nontransfused syngeneic animals. In LEW rats that received three injections of 5 X 10(7) "suppressor" spleen cells, the antibody response to BN blood was strongly impaired as compared with animals that received normal spleen cells. BN or (BN X LEW)F1 skin grafts survived significantly better in multiple transfused LEW rats than in nontransfused controls. This was even more pronounced when ALS was given additionally. Third-party grafts (BUF) survived only slightly better than controls. It is concluded that multiple BT (1) result in humoral anti-donor nonreactivity secondary to an initial antibody response, (2) induce strong specific and weak nonspecific suppressor cell activity, and (3) increase skin graft survival.     

Bone grafts in T-cell deficient rats

Revascularization, new bone formation, and resorption of fresh syngeneic and allogeneic cancellous bone that were transplanted to an intramuscular pouch have been studied in athymic and normal rats. Revascularization was evaluated with radioactive microspheres; formation of new bone was assessed with ⁸⁵Sr incorporation; and resorption was measured by the graft weight reduction. Animals were killed 2, 6, or 12 weeks after transplantation. the circulation and bone formation in allogeneic grafts were greatly impaired in normal rats as compared with the athymic group and the syngeneic grafts. the allografts in normal rats had a smaller weight reduction than the allografts in athymic rats, suggesting impaired resorption. We conclude that the T-lymphocyte system is at least partly responsible for the difference between syngeneic and allogeneic bone grafts, and that the thymus-dependent primary rejection mechanism probably is important for the vitality of allogeneic bone grafts.     

Fresh, frozen, or decalcified bone grafts: a study of early vascularisation and mineralisation of allogeneic and syngeneic bone grafts in rats.

The incorporation of syngeneic and allogeneic bone grafts pretreated by freezing or demineralisation was studied in 10 rats. Fresh, decalcified, or frozen cancellous bone of syngeneic or allogeneic origin was transplanted to intramuscular pouches. Revascularisation was evaluated with radioactive microspheres; formation of new bone was assessed by incorporation of strontium, and resorption was assessed by measuring the reduction of graft weight. Three weeks after grafting, fresh syngeneic and allogeneic bone differed significantly in all three variables. Frozen syngeneic bone was revascularised significantly better than frozen allogeneic bone, but there was no difference in formation of new bone or resorption. There were no significant differences between syngeneic and allogeneic decalcified bone in any of the variables studied. We conclude that differences in incorporation between syngeneic and allogeneic bone grafts are reduced by pretreatment with deep-freezing or demineralisation. Both forms of pretreatment affect the incorporation of the grafts.     

Effect of DSG on xenogeneic immune reactivity with special emphasis on human anti-pig cellular reactions in vitro

Abstract: The effect of the immunosuppressive drug 15-deoxyspergualin (DSG) on xenogeneic human anti-porcine cellular reactivity in vitro, including MLR induced proliferation, interleukin-2 (II-2) production, generation of cytotoxic cells, and the effect on antibody-dependent cellular cytotoxicity (ADCC), were compared with the effects of cyclosporin A (CsA) and/or FK506. The cytotoxic response was evaluated for both direct and indirect pathways for antigen presentation. In addition, the effects of DSG and CsA on antibody production to pig peripheral blood lymphocytes (PBL) in mice was studied. The degree of immunosuppression of xenogeneic and allogeneic cellular responses was compared. CsA and FK506 effectively inhibited proliferation and II-2 production induced by allogeneic human PBL or xenogeneic porcine PBL, whereas DSG did not have any effect on these responses. However, DSG suppressed both the allogeneic and xenogeneic in vitro induced cytotoxic responses, to the same level whether induced via the direct or indirect pathways of immune activation. In contrast, CsA inhibited cytotoxicity induced by xenogeneic cells via the direct but not via the indirect pathway. No effect of FK506 and DSG on ADCC was demonstrated.
A 5-day treatment with DSG or CsA of mice immunized with pig PBL partly suppressed antibody production. In DSG treated mice anti-pig PBL antibodies were produced, but titers were lower than in nontreated or CsA treated mice. The results indicate that DSG may be more effective than CsA/FK506 in inhibiting cytotoxic responses and antibody production induced by xenogeneic pig cells. A possible explanation could be that cytotoxicity induced via the indirect activation pathway of xenoreactivity is mediated to a high degree by CD3^- CD16⁺ (natural killer) NK-like cells, and that stimulation of these cells may be more sensitive to DSG than to CsA/FK506.     

Transplants of rat chondrocytes evoke strong humoral response against chondrocyte-associated antigen in rabbits

Rat chondrocytes transplanted intramuscularly in rabbits produced cartilage. In 1-day-old transplants chondrocytes remained viable. After 1 week peripheral chondrocytes of the transplant were dead and the cartilage was surrounded and resorbed by macrophages. In 2-week-old transplants cartilage deteriorated and was invaded by fibroblast-like cells and macrophages. Sera of rabbits that received two or three consecutive transplants of rat chondrocytes with 2-week intervals contained high titer of antichondrocyte cytotoxic antibodies. A part of the cytotoxic activity could be removed by absorption with rat splenocytes. Western blot analysis of lysates from fresh or 24-h cultured chondrocytes with absorbed sera detected antigen with M(r), of approximately 74 and approximately 23 kDa. Only the latter remained after reduction in 2-mercaptoethanol. In lysates of fibroblasts and endotheliocytes the 23-kDa antigen was not found but the serum reacted with M(r) 39-kDa antigen. In lysates of thymocytes a weak band corresponding to M(r) of 35 kDa was present. Serum from rabbits receiving transplants of living chondrocytes followed by chondrocytes suspended in complete Freund's adjuvant contained antibodies directed against components of crude collagenase used for cell isolation. Such antibodies could not be detected in sera of rabbits receiving transplants of living chondrocytes only. Molecular weight of detected antigen differs from that of collagen type II, core of aggrecan, link proteins, and several other macromolecules of cartilage matrix. It could represent either a component of chondrocyte membrane or a membrane-bound substance resistant to enzymes used for isolation. Availability of antibodies against presumably chondrocyte-specific antigen produced during transplant rejection may help to characterize it more precisely and to ascertain whether its presence may influence results of autogenous chondrocyte transplants in humans.     

Healing of cortical bone grafts in athymic rats.

We studied healing of allogeneic and syngeneic cortical tibial segment grafts in athymic and normal rats. After 3, 6, and 12 weeks, the weight, circulation, and mineralization rate of the healing segment, and mechanical strength and stiffness of the healing tibia were measured. There were no differences between allogeneic and syngeneic grafts in athymic and normal animals at 3 or 6 weeks. After 12 weeks, the vascularization and mineralization of the grafts, but not of the surrounding callus, were smaller in the allogeneic grafts in the normal recipients than in the other groups. Also after 12 weeks, the stiffness of the healing tibiae was less in allogeneic grafts in normal recipients than in the other groups. The strength of the allogeneic grafts was less than the strength of the syngeneic grafts in both athymic and normal recipients. This suggests that T-cell-mediated rejection is responsible for decreased vascularization and mineralization of allogeneic bone and that the difference in strength between allogeneic and syngeneic grafts is not due to T-lymphocyte graft rejection.     

Phenotype, activation status, and suppressor activity of host lymphocytes during acute rejection and after cyclosporine-induced unresponsiveness of rat cardiac allografts

Serial changes in phenotype, cell cycle, and functional behavior of lymphocyte subpopulations occurring both during acute rejection in unmodified hosts and in long-surviving heterotopic cardiac allografts in rats treated with cyclosporine (CsA) were studied. Using flow cytometry, RNA and DNA content of cells was examined during various phases of cell activation. In animals acutely rejecting their grafts, numbers of cells infiltrating the grafts and in host spleen in G1 phase (higher RNA content) increased, starting from day 3, and peaked by 5-6 days posttransplantation, and numbers of cells in S/G2/M phase (higher DNA content) remained stable. Similar, although slightly delayed changes were noted in CsA-treated recipients. The ratio of T helper (Th) to T suppressor/cytotoxic (Ts/c) phenotype cells infiltrating acutely rejecting grafts by day 3, was 1.6; it inverted abruptly to 0.7 by days 5-6, suggesting a preponderance of Ts/c during the later stages of allograft rejection. Ratio inversion occurred slightly later in host spleen and later in peripheral blood. Similarly, treatment with CsA produced a transient depression of Th, with recovery of the Th: Ts/c ratio during weeks 3-4 following transplantation. Adoptive transfer studies were then performed to investigate the functional significance of the T cell subsets. Survival of test grafts was prolonged significantly (ca. 14 days, P less than 0.001) when cells infiltrating grafts and spleen were transferred during inversion of Th:Ts/c; before that period, test graft survival was shortened in a second-set manner. These experiments suggest that suppressor cells may be responsible for resolution of acute rejection, as well as for host unresponsiveness seen after CsA treatment, and they represent an important homeostatic host mechanism following immunological stimulation.     

Allogeneic cell stimulation enhances cytomegalovirus replication in the early period of primary infection in an experimental rat model.

BACKGROUND: Cytomegalovirus (CMV) diseases commonly occur in allograft recipients in the early post-transplant period. However, factors responsible for the high incidence of CMV diseases during this period are not yet fully defined. METHODS: Wistar-Furth (WF; RT-1(u)) rats were inoculated with 10(4) plaque-forming units (PFU) of rat CMV (RCMV) intraperitoneally, and then transplanted with allogeneic lungs from Dark Agouti (DA; RT-1avl) rats or stimulated with 10(7) mitomycin C-treated spleen cells from DA rats by daily sub-cutaneous injections for 2 weeks. No immunosuppressive agent was used. Naive WF rats and WF rats grafted with syngeneic lungs or cells were used as controls. The level of RCMV replication in rats was assessed by infectious virus titers in tissues. RESULTS: The virus titers in salivary glands of allogeneic and syngeneic lung graft recipients were significantly higher than in naive WF rats. The level of RCMV replication in rats stimulated with allogeneic spleen cells was significantly higher than in the syngeneic recipient rats: virus titers in the salivary gland of allogeneic and syngeneic recipients reached 4.61 +/- 0.33 and 4.00 +/- 0.37 log(10) PFU/g tissue, respectively, at 14 days post-infection (p = 0.015). The augmented viral replication in allogeneic recipients was confirmed by an increase in the number of RCMV antigen-positive macrophages present in tissue sections of the salivary gland. CONCLUSIONS: Acute lung allograft rejection and allogeneic spleen cell stimulation enhance CMV replication in the salivary gland of rats. Various responses to allogeneic antigens occurring in the process of acute allograft rejection could be risk factors for post-transplant CMV replication and infection.     

Evidence that indefinite survival of small bowel allografts achieved by a brief course of cyclosporine or FK506 is not due to systemic hyporesponsiveness.

The immunological status of Lewis (LEW) recipients of indefinitely surviving (greater than 400 days) orthotopic Brown-Norway (BN) small bowel allografts was investigated 1 to 1 1/2 years after cessation of immunosuppressive therapy with either cyclosporine or FK506 and compared with recipients of syngeneic grafts. A normal proliferative response (as measured by a mixed lymphocyte culture) of recipient peripheral lymph node lymphocytes in response to the donor-specific (BN) and the third-party (ACI) antigen, was observed in all experimental groups. Cytolytic T cell generation (as measured by a standard 51Cr-release cytotoxicity assay) in response to the donor-specific (BN) and the third-party (ACI) antigen was observed also in all groups. A FACS analysis of allograft-recipient splenocytes showed no evidence for systemic lymphoid chimerism. BN or ACI skin grafts transplanted onto recipients of allogeneic and syngeneic small bowel grafts were rejected completely in 12-17 days, while the intestinal grafts remained functional. Immunohistologic evaluation of the allografts, using anti-BN class I and anti-Lewis class II monoclonal antibodies showed anti-BN staining on the epithelial and endothelial structures, whereas the mononuclear cells in the lamina propria stained positively with the anti-LEW monoclonal antibody. However, lymphoid depletion and scarring of Peyer's patches and mesenteric lymph nodes as well as focal obliterative mesenteric arteriopathy, indicative of an indolent chronic rejection, were observed. These data demonstrate that recipients of indefinitely surviving small bowel allografts remain immune competent and do not retain the intestinal graft on the basis of specific hyporesponsiveness to the donor antigens.     

Revascularisation of bone grafts in rats.

Revascularisation of syngeneic and allogeneic intramuscular bone grafts have been studied using radioactive microspheres to measure the ingrowth of blood vessels. New bone formation and resorption were measured by 85strontium uptake and by graft weight reduction. Revascularisation, and mineralisation rate were significantly higher in syngeneic grafts than in allogeneic grafts at two, three and six weeks after implantation. The syngeneic grafts lost weight faster indicating that the allogeneic grafts resorbed more slowly. The ingrowth of new vessels is impaired in allogeneic bone, and this probably inhibits the rate of bone formation and resorption of the grafts.     

Fetal bone grafts do not elicit allograft rejection because of protecting anti-Ia alloantibodies. Implications to the immune survival of fetuses in allogeneic mothers.

In a previous study we showed that allografts of BN fetal bone, unlike allografts of adult bone, are not rejected by allogeneic recipients of the Lewis strain in spite of the existence of major histocompatibility complex (MHC) incompatibility between donors and hosts. In the present study, we analyzed the relationships existing between the host and fetal tissue that determine graft survival. We found that (1) the fetal BN graft, unlike adult grafts, induces in Lewis recipients a vigorous humoral response consisting mainly in the production of IgG antibody that seems to be directed against antigens of Ia-like specificities. (2) The BN rats are genetically defective in their capacity to respond to determinants and thus are not capable of producing anti-Ia antibodies; in accordance, Lewis fetal bone grafts are rejected by the BN recipients. (3) Chondrocytes isolated from fetal mouse bones do express Ia antigenic determinants. We suggest that the survival of an allogeneic fetal graft in an immunologically intact recipient depends on an active and selective immune response directed against the Ia components associated with the MHC on the embryonic and fetal cells. On the basis of these notions, we propose that the capacity of Ia determinants expressed on cells of the embryo, to elicit anti-Ia and IgG alloantibodies in the pregnant mother, determines the capacity of the embryo to escape rejection by the histoincompatible mother.