Effect of Immunological Differences on Rat Aortic Valve Allograft Calcification

Calcification may be a cause of allograft valve degeneration. To determine whether immunological differences between donor and recipient affect the degree of calcification that occurs, adult Lewis rats received aortic valve allografts transplanted heterotopically into the abdominal aorta. All valves were transplanted immediately after harvest. The valves were not exposed to antibiotics or albumin before insertion. Valve donors were of the Lewis (syngeneic), F344 (weakly allogeneic, RT1 compatible, non-RT1 incompatible), LBN F1 (moderately allogeneic, one haplotype identical, one haplotype incompatible at the RT1 and non-RT1 loci), and Brown Norway (strongly allogeneic, RT1 and non-RT1 incompatible) strains. Valves were harvested 3-12 weeks following transplantation. Scanning electron microscopy and energy dispersion x-ray microanalysis were performed on one leaflet of each valve to evaluate calcium content. Calcium content expressed in counts (mean +/- standard error) according to donor strain were: Lewis, 1642 +/- 233; F344, 4853 +/- 1412; LBN F1, 4714 +/- 823; and Brown Norway, 4358 +/- 835. Significant differences (p less than 0.05) existed between valves from Lewis donors and those from each other strain. No differences among the other strains were statistically significant. It is concluded that syngeneic valve allografts calcify less than allogeneic grafts. However, the degree of allogenicity did not influence the magnitude of calcification.     

Effect of storage at 4 degrees C in a nutrient medium on antigenic properties of rat aortic valve allografts

The effects of prolonged storage at 4 degrees C in nutrient medium on the antigenic properties of aortic valve allografts are unknown. Lewis rats received heterotopic aortic valve allografts from Brown Norway donors. Valves were transplanted immediately after harvest (fresh), or after antibiotic sterilization and storage in a nutrient medium at 4 degrees C for 3, 7, 14, or 21 days. Additional rats underwent sham laparotomy (sham). All recipient rats received Brown Norway skin grafts 3 weeks after valve transplant or sham procedure. Time to skin graft rejection for all groups was as follows: fresh (n = 10), 4.5 +/- 0.9 days; sham (n = 10), 7.1 +/- 0.3 days; 3-day (n = 10), 4.9 +/- 0.3 days; 7-day (n = 10), 5.2 +/- 0.4 days; 14-day (n = 10), 6.1 +/- 0.7 days; and 21-day (n = 10), 6.0 +/- 0.6 days. Significant differences existed between the sham group and each of the transplanted groups. No significant differences existed between the fresh group and either the 3-day or 7-day groups. The difference between the fresh group and the 14-day group approached significance (0.05 less than p less than 0.10), and the difference between the fresh and 21-day groups was significant (p less than 0.05). Additional valves not used for transplantation were studied with scanning electron microscopy. The valves preserved in nutrient medium exhibited a progressive loss of endothelium as compared with fresh valves. Storage of aortic valve allografts in a nutrient medium at 4 degrees C is associated with a progressive attenuation of antigenic response.(ABSTRACT TRUNCATED AT 250 WORDS)     

The extent of immunological privilege of orthotopic corneal grafts in the inbred rat

Corneal grafts are believed to enjoy a degree of "immunological privilege" primarily due to the avascularity of the recipient bed. In this study orthotopic full-thickness corneal grafts were carried out in the inbred rat, using a technique that is a close model of corneal grafting in humans. The survival times of corneal grafts on nonvascularized beds of 28 fully allogeneic strain combinations were determined without the use of immunosuppression. Some combinations were rejected rapidly, e.g. DA (RT1a) into BN (RT1n) with a mean survival time (MST) +/- SD of 7.8 +/- 1.3 days, and some at a moderate rate, e.g. AO (RT1u) into LEW (RT1l) with an MST of 23.1 +/- 10.0 days, whereas in other cases survival was indefinite, e.g. WAG (RT1u) into PVG (RT1c), an MST of greater than 100 days. Orthotopic corneal grafts on nonvascularized beds between DA and AO parents and the F1, followed the basic rules of transplantation genetics. In addition, the rate of graft rejection was significantly faster (P less than 0.001) with corneal grafts from DA into AO placed onto a vascularized compared with a nonvascularized corneal bed (MST of 6.8 +/- 2.4 or 12.1 +/- 4.0 days respectively). The rate of rejection of corneas on a vascularized bed was at a similar rate to that of orthotopic skin or heterotopic auxiliary heart grafts. The results indicate that the fate of a corneal allograft on a nonvascularized bed is dependent upon the particular combination of donor and recipient strain. No consistent association was observed between any donor or recipient RT1 haplotype and survival; this suggests that non-RT1 background genes may play a role in the survival of corneal grafts.     

Cryopreservation does not alter antigenic expression of aortic allografts

Cryopreserved aortic homografts are reportedly viable, but no cross-matching or immunosuppression is utilized. Alterations of the antigenic expression by cryo-preservation must be assumed. We designed a protocol to test this premise. Fisher 344 rats served as recipients in all cases. Lewis rats, a mildly disparate strain, were utilized as donors. Four cohorts of animals were utilized. Group I (N = 11) served as a "first set" control. All animals received a syngeneic skin graft. After 28 days an allogeneic skin graft was placed; rejection was seen at 10.3 +/- 0.5 days. Group II (N = 16) first received allogeneic skin grafts with a similar "first set" rejection pattern of 10.4 +/- 0.47 days. A second skin graft was placed and demonstrated an accelerated rejection response of 6.06 days +/- 0.25 days. Group III (N = 17) received two leaflets from a "fresh" Lewis heart valve inserted into a subcutaneous pouch. Allogeneic skin grafts in this group demonstrated a similar second set rejection at 7.05 +/- 0.82 days. Group IV (N = 22) also underwent implantation of heart valve leaflets, except "cryopreserved" Lewis leaflets were implanted into the subcutaneous pouch. An allogeneic skin graft was placed and demonstrated a second set rejection at 7.18 +/- 0.39 days. A one-way analysis of variance shows no significant difference in Groups III and IV, but a significant difference with respect to Group I (P less than 0.00001). Cryopreservation does not alter the antigenic expression in this model, and at present we strongly recommend that at least ABO compatibility be utilized in all patients undergoing aortic homograft implantation.     

Studies on the antigenicity of vital allogeneic valve leaflet transplants in immunogenetically controlled strain combinations.

The use of defined inbred strains of rats enables reproducible experimentation on the antigenicity of heart valve leaflet transplantation. The inbred strains CAP, F344, and LEW were used as syngeneic, weakly allogeneic (RT-1-identical) and strongly allogeneic (RT-1-incompatible) strain combinations. After heart valve leaflet transplantation, humoral and cell-mediated immune responses were investigated. The results were: (1) Allogeneic heart valve leaflets are antigenic. (2) Just one heart valve leaflet, applied intravascularly induces sensitization of the recipient. (3) In the weakly allogeneic system, sensitization is only revealed by donor-specific skin transplants, while in the strongly allogeneic group, sensitization is demonstrated humorally as well. (4) The greater the immunogenetical difference, the sooner sensitization appears. In the strongly allogeneic system, skin transplants were rejected as "white grafts".     

Orthotopic liver allografts in the rat. The influence of strain combination on the fate of the graft

This report describes the fate of orthotopic liver allografts performed in 22 donor/recipient strain combinations. Of these, 2 were major histocompatibility complex (MHC)-congenic, 18 were fully allogeneic, and 2 were non-RT1 incompatible combinations considered to differ only in minor transplantation antigens. The fate of fully allogeneic liver grafts was strictly dependent on the donor/recipient strain combination, and survival times fell into three nonoverlapping groups corresponding to acute rejection (8-21 days), delayed rejection (28-63 days), and prolonged survival (greater than 100 days). Serial levels of recipient serum enzymes also fell into groups corresponding to the fate of the graft. In 7 fully allogeneic donor/recipient combinations, liver grafts showed very prolonged survival. In five combinations they were rejected almost as quickly as kidney or heart grafts. In the two MHC congenic combinations, liver grafts survived for prolonged periods. In the non-RT1-incompatible combinations, unexpectedly, PVG livers were rejected by AUG recipients. MHC-incompatible liver grafts of a given strain survived for long periods or were rejected (in acute or delayed fashion) depending on the recipient strain. This behavior is unique to liver amongst commonly transplanted vascularized organs, and the fate of the graft clearly indicates strain-dependent levels of recipient responsiveness to defined transplantation antigens. Independent evidence supporting this conclusion is discussed. Apparently anomalous results of liver grafting in certain strain combinations are briefly considered.     

Major-histocompatibility-complex-restricted male skin graft rejection responses in rats

Normal DA (RT1a) female rats rejected male skin isografts when preimmunized with RT1-compatible DA, or ACI (RT1a) male bone marrow cells (BMC), but failed to reject them when preimmunized with RT1-incompatible PvG/c (RT1c), F344 (RT1lvl), or BN (RT1n) male BMC--as well as when they were untreated. DA female rats rendered neonatally tolerant to RT1-incompatible PvG/c female tissues failed to reject, not only DA, but also PvG/c male skin grafts when preimmunized with PvG/c male BMC. DA female rats tolerant of PvG/c female tissues that had rejected DA male skin grafts following immunization with DA male BMC failed to reject PvG/c male skin grafts. These results indicate that in rats, unlike mice, male skin graft rejection responses are MHC-restricted, at least in the DA strain.     

Cellular immunity to heterotopic corneal allografts in the rat

Although the immune nature of corneal allograft rejection has been recognized for over thirty years, the specific mechanisms involved in such reactions remain obscure. We investigated the cellular immune responses of PVG (RT1c) rats that were grafted with fully allogeneic ACI (RT1a) skin, ACI cornea, or PVG cornea to the chest wall or given sham grafts. Cell-mediated lymphocytotoxicity (CML) was tested at 10 days posttransplant by placing recipient spleen cells in culture with irradiated ACI stimulator cells, and six days later measuring specific lysis of 51Cr-labeled target lymphoblasts at several effector-to-target ratios. Effector cells from animals receiving allogeneic skin or cornea grafts lysed targets from the donor (ACI) strain at levels significantly (P less than 0.01) above those obtained using effectors from control (sham grafted or syngeneic corneal graft recipient) animals. Significant lysis was also seen using target cells from PVG.1A (RT1a) or PVG.R1 (RT1r1) congenic rats, which differ from recipients only at the RT1 complex and the RT1.A (class I antigen) region, respectively. Stimulator cells from PVG.1A and PVG.R1 animals also permitted detection of specific responses in secondary CML, but syngeneic PVG stimulators did not, indicating that in vitro restimulation of effector cells can be met by using stimulator cells bearing only allogeneic class I major histocompatibility complex (MHC) antigens. These results indicate that corneal allografts evoke specific cellular immune responses in the rat, and that class I MHC antigens act as effective targets for these responses.     

Allograft Conduit Wall Calcification in a Model of Chronic Arterial Graft Rejection

A bstract Early allograft vascular wall degeneration has emerged as a major important complication in young patients. To explain this mechanism, we reviewed studies on explants of allograft valved conduits implanted heterotopically into the infrarenal aorta in inbred rats (LEW;RT1, and CAP-RT1°C). The following strain combinations (isografts and allografts) were used: syngeneic, LEW-> LEW, strongly allogeneic, and CAP > LEW (RT1- and non-RT1-incompatible). Second-set skin grafting was performed 3 weeks after the heterotrophic implant to test for immunogenicity and presensitization. The animals (LEW) were sacrificed serially on days 20, 30, 50, and 100 for immunofluorescence and SEM studies. Endothelial disruption was observed on day 30, while valve leaflets appeared normal. Humoral allograft rejection was demonstrated and associated with production of antibodies (IgG) against the endothelial cells and around the smooth muscle cells, and in areas of smooth cell necrosis, through 100 days. Neointimal repopulation by host cells and migrated smooth muscle cells was also observed in both viable and allovital grafts. Allovital grafts demonstrated more disorganized collagen and elastic fibers, as well as calcific degeneration in the media and neointima on day 50; the viable conduits showed such structural changes on day 100. In conclusion, vascular walls of allovital conduits calcified earlier than the viable conduits without discernible calcification of the valves. There is therefore evidence to prove causative relationships between cellular viability, immune response, and fibroproliferative calcific degeneration in allograft vascular conduits.     

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.     

A new method of bone marrow transplantation leads to extension of skin allograft survival

Tolerance induction through allogeneic bone marrow transplantation is an alternative method to chronic immunosuppression in maintaining long-term allograft survival. In this article, we introduce a new method of bone marrow allotransplantation, which preserves its natural microenvironment and does not require marrow processing or recipient conditioning. A total of 43 skin graft transplantations were performed in nine experimental groups between isogeneic [Lewis to Lewis (LEW, RT1(1))] and allogeneic [Lewis x Brown Norway (LBN --> F1, RT1(1+n)) to Lewis] rats under 35-day protocol of alphabeta T-cell receptor (TCR) monoclonal antibody (mAb) and cyclosporine (CsA) protocol. Monotherapies combined with "crude" bone marrow transplantation resulted in extended survival up to 21 days under CsA and up to 10 days under alphabeta-TCR mAb protocol. The use of combined protocol of alphabeta-TCRmAb/CsA with crude bone marrow transplantation resulted in the extension of skin allograft survival up to 65 days (P < .05). This new simple method of "crude" bone marrow allotransplantation without recipient conditioning is a promising, minimally invasive technique with a potential for direct clinical application.     

Procollagen synthesis by fresh and cryopreserved rat pulmonary valve grafts

OBJECTIVE: Allograft valves are frequently used in the repair of congenital cardiac anomalies. The failure rate may differ depending on the type of allograft used. Previous studies have shown that rat aortic valve grafts exhibit synthesis of procollagen, suggesting a capacity for repair and regeneration after implantation. No studies of pulmonary valve grafts in the heterotopic rat implant model have thus far been reported. This study was designed to investigate whether pulmonary valve grafts maintain in vivo viability, as demonstrated by procollagen synthesis, and whether cryopreservation, histocompatibility, or both affect this property. METHODS: Cryopreserved and fresh rat pulmonary valves were implanted into the abdominal aorta of syngeneic and allogeneic recipients. The grafts and native valves were excised 3 to 21 days after implantation. Valves were sectioned and immunohistochemically stained for procollagen. Computerized morphometry was used to calculate changes in intima, media, and adventitia as a percentage of cross-sectional area of the graft. Procollagen content was graded by semiquantitative methods. RESULTS: Pulmonary valve grafts had significantly greater collagen density in the intima and adventitia compared with native aortic and pulmonary tissues, but collagen density in the media was similar in all groups. The grafts demonstrated appreciably greater procollagen than the corresponding native valves. These findings were consistent in all grafts (ie, both fresh and cryopreserved, both syngeneic and allogeneic), irrespective of duration of implantation. CONCLUSIONS: Procollagen synthesis occurs in pulmonary valve grafts early after implantation, indicating viability of these tissues. This model of pulmonary valve implantation may have wide applicability to questions of allograft biology.     

The relative roles of MHC and non-MHC genes in heart and skin allograft survival

Although the role of the major histocompatibility complex (MHC) of the rat (RT1) in graft rejection has been established, the role of non-RT1 genes is not well understood. To investigate the influence of MHC and non-MHC genes in graft rejection, various combinations of congenic and inbred strains of rats were used as donors and recipients of skin grafts and perfused abdominal heart grafts. In addition, hemagglutinating and cytotoxic antibody responses were evaluated to assess loci that were serologically active in transplantation. Our results demonstrate that: (1) RT1 antigens are the most important determinant in heart and skin rejection; (2) antigens controlled by non-MHC genes also play a major role in rejection because they cause disparate heart grafts to be rejected by day 18 and skin grafts by day 26; (3) RT2 cell antigens alone do not cause graft rejection; and (4) allogeneic differences at the RT1, RT2, RT3, and RT6 loci elicit an antibody response in heart transplantation.     

Induction of indirect donor-specific hyporesponsiveness by transportal RT1-peptide pulse in rat skin transplantation

In the present study, we examined whether transportal pulse of class I major histocompatibility complex (MHC) allopeptides can induce indirect (non-chimeric) donor-specific hyporesponsiveness, using a high-responder rat skin transplantation model. Two donor-specific 8-amino acid peptides corresponding to residues 58-65 and 70-77 in the alpha(1) helical region of RT1.A(a) were synthesized. In order to test immunogenicity of these peptides, mixed lymphocyte reaction (MLR) was performed. Then, 100-microg portions of peptides were injected into recipient Lewis (LEW, RT1.A(l)) rats via the portal vein 14 days before skin transplantation. Skin allografts from August Copenhagen Irish (ACI, RT1(a)) or Wistar King A (WKA, RT1(k), third-party) donors were transplanted to LEW (RT1(l)) recipients. Transportal pulse of residues 58-65 and 70-77 prolonged graft survival significantly in ACI-to-LEW skin transplantation (17.6+/-0.40 and 18.0+/-0.45 days) compared with control (14.2+/-0.37 days). However, pulse of residues 106-113, a non-donor-specific control, did not prolong graft survival time (14.6+/-0.40 days) in the same combination. Regarding the third-party donor, residues 58-65 injected into LEW recipients had no effect on survival time of skin grafts (19.0+/-0.84 days) derived from WKA donors compared with the untreated WKA-to-LEW control (19.4+/-0.93 days). Transportal pulse of RT1.A(a) peptides induced donor-specific hyporesponsiveness even in a high-responder rat skin transplantation model. Our results suggest that graft enhancement by transportal exposure to donor cells may not be induced by a chimeric process but, instead, by an indirect mechanism not involving intervention of viable donor cells.     

Sex-associated differences in the survival of skin grafts in rats. Enhancement of cyclosporine immunosuppression in male compared with female recipients

Focusing on sex-difference in prolongation of allograft survival time, we have performed skin grafts between fully allogeneic rat strains, AO (RT1u) and DA (RT1a) with an immunosuppressant, cyclosporine. Isografted skins survived indefinitely, whereas allografts were severely rejected at days 7-9 without immunosuppressive treatment. When adult male DA rats received CsA (15 mg/kg/day, i.m., for 14 days postoperatively), allogeneic skin was accepted from either male or female AO rats for 38.8 +/- 20.5 days (mean survival time [MST] +/- SD) and for 44.7 +/- 43.3 days (MST +/- SD), respectively, with normal hair growth at around day 17. Additional CsA administration every 5 days after the initial short course treatment was also effective in preventing chronic rejection. Male AO rat skin grafted onto adult male DA rats survived for over 50 days as long as the treatment was carried out. In contrast, when adult female DA rats were used as recipients, only a few days' prolongation was observed in comparison with a non-treated group. The rejection always occurred, even during the initial course of treatment (MST +/- SD): 10.9 +/- 1.6 days). Younger male DA recipients, 5 and 10 weeks old, rejected AO skin within a shorter time, depending on the age. The maximal graft survival was observed when male adult rats more than 14 weeks old were used as recipients. On the other hand, the CsA serum level of female recipients at day 14 was considerably lower than that of males. However, even when the level of females was adjusted to that of males by the administration of a double dosage (30 mg/kg/day), the female recipients consistently rejected the skins (MST +/- SD: 14.5 +/- 1.9 days). Therefore, these results clearly indicate that this male-associated immunosuppressive effect depends upon the sex and age of the recipient animals.     

Experimental small bowel transplantation using newborn intestine in rats: III. Long-term cryopreservation of rat newborn intestine

BACKGROUND: If long-term organ cryopreservation can be attained, a significant achievement will have been made to address the problem for donor shortage. Fetal intestine has been known to revascularize naturally without vascular anastmosis. The authors have confirmed previously that the newborn intestine also could develop to maturity in the host omentum. Here, the authors examined whether the cryopreserved newborn intestine could revascularize in the syngeneic combination using the 2 different solutions and whether cryopreservation affect their antigenicity in the allogeneic combination. METHODS: Inbred rat strains of LEW (MHC haplotype; RT1(l)) and BN (RT1(n)) were used. LEW newborn intestinal grafts were stored in RPMI-1640 or University of Wisconsin solution with 10% DEMSO (n = 10 in each group). The grafts were placed into a cold (4 degrees C) preservation solution for 30 minutes and then placed into a freezing chamber and cooled to -80 degrees C at -1 degrees C/min after 12 hours quenched to -180 degrees C in liquid nitrogen for longer than 30 days. Then, the cryopreserved grafts under the 2 different solutions were transplanted syngenicaly (LEW to LEW). The cryopreserved BN grafts also were implanted into the LEW omentum pouch. The allotransplantation was received with a 14-day high-dose course of tacrolimus (0.64 mg/kg, intramuscularly). The grafts were evaluated histologically at 4 weeks after transplantation. Fresh newborn intestines implanted in this syngeneic and allogeneic combination were evaluated as each control group. RESULT: In the syngeneic combination, more than 90% of the mature intestine were obtained. There was no significant difference among the different solution and the fresh group. However, in the allogeneic combination, both fresh and cryopreserved grafts were histologically poor. CONCLUSIONS: This is the first report showing that long-term cryopreservation was not harmful for neovascularization of newborn intestine. Long-term cryopreservation did not reduce the antigenicity of the newborn intestine. J Pediatr Surg 36:602-604.     

Lung allograft rejection in the rat. II. Specific immunological properties of lung grafts

The immunological mechanism of lung allograft rejection was studied in inbred rats, in order to explain the rapid progress of the rejection response against RT1-incompatible lung grafts. Histological appearances of the graft and of the recipient's spleen were studied, migration patterns of graft and recipient lymphocytes were assessed, and titers of circulating alloantibodies were determined. Histologically, we discriminated four phases of the rejection response in lung grafts: sequentially the latent, vascular, alveolar, and destruction phases. Early in the vascular phase, recipient lymphocytes primarily infiltrated the bronchus-associated lymphoid tissue (BALT) of the graft, causing a local immune response. Concurrent with these local rejection phenomena in the graft, a strong systemic immune response developed in the recipient's spleen, presumably induced by the great number of lymphocytes that migrated from the graft's BALT into the recipient's lymphoid tissues. We conclude that BALT facilitates a fast and intensive interaction between lung graft and recipient that is likely to accelerate the induction of the rejection response both locally in the graft and systemically in the recipient's lymphoid organs.     

Acceptance of allogeneic fibroblasts in skin equivalent transplants

Living skin equivalents (SE) were prepared by combining cultured fibroblasts with a collagen matrix and overlaying this lattice with keratinocytes. SEs prepared using allogeneic female rat fibroblasts or xenogeneic rabbit or human fibroblasts and keratinocytes isogeneic to the graft recipient were transplanted to recipient male rats. Biopsies of some of these SE grafts were examined histologically at intervals ranging from 5 days to 2 months. Biopsies of other grafts were done, and fibroblasts grown from them were karyotyped to determine the percentage of donor fibroblasts remaining in the graft. SEs containing xenogeneic fibroblasts were rejected. Allografted fibroblasts in SEs were accepted by recipient rats after a transient mononuclear cell response. A second SE allograft from the same donor strain did not provoke rejection either in the original allograft or in the challenge allograft. A secondary graft of allogeneic skin did not provoke rejection in the original SE graft, although the skin graft was rejected. Grafting the recipient first with allogeneic skin and then with the SE allograft led to rejection of the skin but not of the SE graft, ruling out the possibility that suppressor T cells were responsible for SE allograft acceptance. Allografted fibroblasts in SEs do not provoke a rejection response, even in presensitized animals, do not render the recipient tolerant to allogeneic skin, and do not act as targets when active rejection is taking place. We propose that cells bearing class I antigens may be acceptable graft constitutents if incorporated in a tissue equivalent excluding cells with class II antigens.     

Histological and immunohistological study of cryopreserved aortic valve grafts: the possibility of a clinical application for cryopreserved aortic valve xenograft

The influence of preservation techniques on xenogeneic immune responses was examined to investigate the possibility of their clinical use. Mongrel dogs and pigs were used as allogeneic and discordant xenogeneic donors of aortic valve grafts, respectively. The allografts and xenografts were implanted in the abdominal aorta of mongrel dogs after cryopreservation or after fresh preservation. Allografts and xenografts were explanted at Days 7 and 42 for histological and immunohistochemical examination. In the fresh preserved allografts and the fresh preserved xenografts, the media of aortic wall grafts were significantly acellular at 7 days. Significant aortic medial destruction and neointimal proliferation with significant destruction of the valve leaflets was observed at 42 days. However, no differences were found among the preservation techniques in the xenogeneic grafts. To alleviate the lack of homografts, approaches such as the tissue-engineered graft may become an alternative in patients who are acceptable candidates.     

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.