A comparison of heterotopic and orthotopic intestinal transplantation in rats

Two surgical techniques are commonly used for small intestinal transplantation: heterotopic (accessory) intestinal grafting (HIT), where the small bowel is initially defunctioned with restoration of intestinal continuity at a later date, and orthotopic (in continuity) intestinal grafting (OIT), where the small bowel is immediately anastomosed to the native intestine. The present experiments were undertaken to compare the advantages and disadvantages of these two surgical models. Graft barrier function (intestinal permeability), intestinal histology, and graft survival were evaluated after heterotopic and orthotopic intestinal transplantation in the following groups of rats: group 1: isografts, group 2: untreated allografts, group 3: low-dose cyclosporine-treated allografts (subcutaneous CsA 2 mg/kg/day), and group 4: high-dose CsA-treated allografts (subcutaneous CsA 4 mg/kg/day). Intestinal permeability was consistently higher after HIT than OIT in all of the groups (ANOVA; P less than 0.01). Histological evidence of rejection appeared earlier after HIT than OIT (HIT 5th postoperative day (POD); OIT 7th POD; P less than 0.05). The mean survival of untreated allografts was longer after HIT than OIT (HIT 15.7 +/- 6 days, OIT 9.2 +/- 1 days, P less than 0.05). The rats treated with low-dose CsA after OIT lost weight and died of rejection after a mean survival time of 17.7 +/- 2 days, while the rats treated with low-dose CsA after HIT remained well until sacrifice on POD 28 (P less than 0.01). The rats with isografts and rats with allografts treated with high-dose CsA remained well after HIT and OIT until sacrifice on the 28th POD. These data suggest that nutrients and other factors in the succus entericus may improve gut barrier function and delay the onset of rejection after OIT. However, rejection of the orthotopic intestinal graft is usually fatal, while rejection of the heterotopic graft is often surprisingly well tolerated. These factors must be taken into consideration when choosing a surgical technique for intestinal transplantation in humans.     

肝细胞生长因子对移植小肠通透性及细菌易位的作用

目的探讨肝细胞生长因子（hepatocyte growth factor,HGF）对移植小肠通透性及细菌易位的作用。方法以Wistar大鼠20只为受体,SD大鼠20只为供体行异位全小肠移植,并以环孢素A（6mg/kg.d）肌注抑制排斥反应。HGF组（n=10）用微量输液泵持续均匀输入HGF（150μg/kg.d）,对照组（n=10）输入等量生理盐水,随机选取同批正常Wistar大鼠作为正常基准（n=10）。第7天两组实验动物均分别以乳果糖/甘露醇液2ml（含乳果糖100mg、甘露醇50mg）行移植小肠灌注,采集24h尿液检测乳果糖、甘露醇含量及乳果糖/甘露醇比值;第8天采集移植小肠肠系膜淋巴结及门静脉血行细菌培养,小肠组织学观察。结果对照组尿液中乳果糖含量为0.0931%±0.0085%,乳果糖/甘露醇比值为0.132±0.021,与正常基准0.0150%±0.0020%和0.020±0.005比较,差异均有统计学意义（P〈0.05）;HGF组乳果糖含量为0.0396%±0.0090%,乳果糖/甘露醇比值为0.056±0.013,与正常基准比较差异均有统计学意义（P〈0.05）,且低于对照组（P〈0.05）。HGF组移植小肠肠系膜淋巴结细菌阳性率为10%,对照组为60%,差异有统计学意义（P〈0.05）。HGF组门静脉血细菌阳性率为10%,对照组为20%,差异无统计学意义（P〉0.05）。两组移植小肠组织学观察仅见少量炎性细胞浸润。结论HGF能够降低同种移植小肠的通透性及细菌易位率,改善小肠黏膜屏障功能。     

The immunomodulatory effect of cryopreservation in rat tracheal allotransplantation.

BACKGROUND: Cryopreservation is one solution to the problem of donor organ deficit. To investigate the effect of cryopreservation on tracheal allografts, we performed 2 experiments in rats. METHODS: In Experiment 1, we assessed second-set graft rejection. Two weeks after primary heterotopic transplantation (Group 1, fresh isografts; Group 2, fresh allografts from Lewis rats; and Group 3, cryopreserved allografts from Lewis rats; n = 5, respectively), each animal underwent secondary heterotopic grafting with isografts and allografts from Lewis and Wistar Furth rats (n = 5, respectively). Four weeks after the secondary transplantation, all grafts were retrieved for histologic analysis. In Experiment 2, we assessed the long-term results of allograft cryopreservation, without immunosuppression therapy. Six months after transplantation of fresh (Group 4) and cryopreserved (Group 5) allografts, the tracheal segments (each group, n = 5) were histologically evaluated. RESULTS: In Experiment 1, only the secondary allografts from Lewis rats in Group 2 did not maintain lumen structure and often showed dislocated or destroyed cartilage. Second-set graft rejection was specifically recognized in Group 2, but not in Group 1 or 3. In Experiment 2, the cryopreserved allografts appeared almost normal and lumen rigidity was preserved 6 months after transplantation. These allografts were superior to the fresh allografts in patency and in cartilage dislocation and mononuclear cell infiltration scores, but not in the viable chondrocyte ratio. CONCLUSIONS: We conclude that cryopreservation may produce successful long-term results because of its immunomodulatory effect on tracheal allografts.     

The level of FC receptor leukocytes in primary and secondary skin allograft recipients.

DA (Ag-B4) rats were grafted with allogeneic Lewis (Ag-B1) skin on the region of the thorax drained by the left brachial and axillary lymph nodes. A DA isograft was placed on the right side of the thorax. From 1 to 14 days after grafting the rats were either given injections of colloidal carbon, killed, and spleen and lymph nodes were assayed for noncarbon-containing Fc rosette-forming leukocytes (RFL), or allowed to complete rejection of the graft. In order to assess secondary allograft rejection within the latter animals after the grafted areas was healed, a second Lewis allograft was placed in the same region as the first and another DA isograft on the right side. Compartmental Fc RFL were enumerated 2 to 16 days thereafter by rosette formation with erythrocyte-antibody. The regional lymph nodes of animals rejecting a primary allograft exhibited a significantly (P less than 0.05) higher level of Fc RFL compared with their contralateral controls. These higher levels were evident on days 6 to 8 and disappear by day 10. However, animals undergoing a secondary allograft response exhibited significant differences by day 4. A greater density of Fc RFL were also evident in cryostat sections of the graft bed of allografts as opposed to isografts.     

51Cr-EDTA: a marker of early intestinal rejection in the rat

Intestinal permeability was studied after accessory intestinal transplantation in Lewis rats. Five groups were evaluated: Group 1--isografts (N = 6); Group 2--Lewis X Brown Norway F1 (LBN-F1) allografts (N = 6); Group 3--isografts treated with CsA 2 mg/kg/day X 10 days (N = 6); Group 4--LBN-F1 allografts treated with CsA 2 mg/kg/day X 10 days (N = 6); Group 5--LBN-F1 allografts treated with CsA 4 mg/kg/day X 28 days (N = 6). Chromium-labeled ethylenedimianetetraacetate (51Cr-EDTA) was given through the proximal stoma of the graft. Renal clearance of 51Cr-EDTA and mucosal biopsies were followed post-transplant. The biopsies of the intestinal graft showed no rejection in Groups 1, 3, and 5; fulminant rejection in Group 2; and mild atypical rejection in Group 4. 51Cr-EDTA clearance was elevated in all groups during the first 7 days post-transplant. Thereafter, 51Cr-EDTA excretion fell to lower levels in the animals with histologically normal grafts (Groups 1, 3, and 5). 51Cr-EDTA excretion in Group 4 was increased with the first histological evidence of rejection on Day 14 and remained elevated until sacrifice (P less than 0.02 compared to Groups 3 and 5). A transient permeability defect occurs after intestinal grafting. Once the graft has recovered from this injury, 51Cr-EDTA is a sensitive marker for intestinal rejection.     

Small bowel transplantation promotes bacterial overgrowth and translocation

Alterations in the symbiotic relationship between immunocompromised hosts and their resident gut microflora may lead to serious complications following small bowel transplantation (SBT). This study examined the effects of SBT and cyclosporine (CsA) immunosuppression on gut bacterial populations and translocation to the mesenteric lymph nodes. Sixty adult male meat-fed Lewis rats were divided into six groups: normal controls, CsA alone (24 mg/kg im qod), CsA carrier vehicle alone, isografts, isografts given CsA, and allografts given CsA. Rats were killed after 3 weeks and segments of small bowel and colon were harvested for quantitative tissue culture. Mesenteric lymph nodes and blood were cultured to identify translocation. Transplantation alone led to an increase in gram-negative aerobes from 2.6 to 4.6 colony forming units/100 mg tissue (P less than 0.05) in the distal ileum (transplanted segment). Eighty-four percent of transplanted animals receiving CsA had bacteria recovered from their mesenteric lymph nodes compared to none in controls (P less than 0.001) and 20% in isografts not receiving CsA (P less than 0.02). Intestinal transplantation alone appears to promote gram-negative overgrowth while the addition of CsA therapy facilitates translocation to the mesenteric lymph nodes and may predispose to gut-associated sepsis following SBT.     

Endotoxin in the peripheral blood during acute intestinal allograft rejection

Intestinal rejection is associated with increased gut permeability and bacterial translocation. The present study examined endotoxin and proinflammatory cytokines in the peripheral circulation during acute intestinal rejection. Heterotopic intestinal transplants were performed using Lewis rats (RT1¹) as donors and DA rats (RT1^a) as recipients. DA rats with intestinal isografts were used as controls. Serum samples were obtained at sacrifice on postoperative days (POD) 7 and 14. Lipopolysaccharide (LPS) was measured using the limulus amoebocyte lysate assay. Interleukin-1 (IL-1) and 6 (IL-6) and tumor necrosis factor- (TNF-) were measured using bioassays. Large amounts of LPS were detected in the serum of intestinal allograft recipients concurrent with the development of graft rejection. Serum IL-6 and TNF- levels were significantly elevated in the allograft recipients on both POD 7 and 14 when compared to DA isografts (P<0.05). Serum IL-1 activity was not detected in the allograft or isograft recipients at either of the two time points. Further studies are warranted to determine the role of intraluminal bacteria and their products in the pathophysiology of intestinal allograft rejection.     

Structure and function of orthotopic small bowel allografts in rats treated with cyclosporine

Previous studies of small bowel transplantation using a variety of animal models and immunosuppressive regimens have failed to demonstrate consistently prolonged survival of bowel allografts capable of maintaining a normal nutritional state. In the present study, total orthotopic small bowel transplantation was performed in inbred rat strains to determine the structure and function of intestinal allografts using cyclosporine for immunosuppression. Without cyclosporine, Lewis-Brown Norway and Brown Norway allografts were quickly rejected by Lewis recipients, resulting in host death. A 15 mg/kg dose of cyclosporine given intramuscularly immediately after operation and for 6 successive days thereafter achieved prolonged but not uniformly indefinite animal and graft survival with clinical courses and pathologic findings consistent with chronic rejection. With continuation of cyclosporine every other day until day 28, all Lewis recipients of Brown Norway allografts were alive and well 8 months after transplantation. Weight gain, maltose absorption, and multiple nutritional indices in these animals were not significantly different from those of either age-matched normal Lewis rats or recipients of Lewis isografts. Full-thickness biopsy specimens of these allografts showed no evidence of graft rejection. These results demonstrate that indefinite survival of intestinal allografts with preservation of their structure and function sufficient to allow normal growth and weight gain can be achieved with cyclosporine therapy. This success in the rat model of orthotopic small bowel transplantation suggests that clinical small-bowel transplantation may become possible using cyclosporine.     

The effect of E coli virulence on bacterial translocation and systemic sepsis in the neonatal rabbit model

In the surgical neonate, three factors that promote bacterial translocation and systemic infection are: (1) intestinal bacterial colonization and overgrowth; (2) compromised host defenses; and (3) disruption of the mucosal epithelial barrier. The newborn rabbit provides an excellent model to study these factors. Like the human, there is early closure of the gut mucosa to macromolecules, and nutrition can be maintained by breast or formula feeding. This study examines translocation and systemic sepsis after colonization with virulent K1 and avirulent K100 strains of Escherichia coli. New Zealand white rabbit pups (2 to 5 days old) were studied. The gastrointestinal tracts of 12 were colonized with K1 E coli; 14 were colonized with K100 E coli; 12 control animals were not inoculated. Mesenteric lymph node (MLN), liver, spleen, and colon homogenate were cultured 72 hours postinoculation. No bacteria were isolated from the colons of all but one control animal. Translocation or systemic sepsis did not occur. Translocation to the MLN was significantly increased (P less than .03) in K1 (50%) and K100 (36%) groups compared with controls (0%). Translocation to liver and spleen (systemic sepsis) was significantly increased (P less than .03) in K1 animals (67%) compared with K100 (0%) or controls (0%). Colonization by both strains of E coli led to translocation to the MLN, but only K1 E coli caused systemic sepsis. This suggests that although colonization by E coli in the newborn leads to translocation to the MLN, progression to systemic sepsis is the result of characteristics of the bacteria and/or neonatal host responses.     

Effect of sarpogrelate hydrochloride,a 5-hydroxytryptamine2 receptor antagonist,on allograft arteriosclerosis after aortic transplantation in rats

BackgroundSarpogrelate hydrochloride, a 5-hydroxytryptamine₂ receptor antagonist, is known to prevent serotonin-induced neointimal hyperplasia. We examined the effect of this agent on allograft arteriosclerosis in a rat model of aortic transplantation.MethodsRats were given an aortic isograft or allograft and oral administration of either saline vehicle alone or 20 mg/kg daily of sarpogrelate for 8 weeks. The grafts were then harvested, and the lumen diameter and the thickness of the intima and media were measured. Comparisons were made between measurement results in isografts and allografts from rats treated and not treated with sarpogrelate. Immunohistochemistry assessments were used to detect expression of serotonin in graft specimens.ResultsFor both allografts and isografts, significantly less intimal thickening was observed in specimens from rats given sarpogrelate compared with rats given saline. Sarpogrelate had no effect on medial thickening in either graft type. Serotonin was detected in allografts from rats given saline alone but not in allografts from rats given sarpogrelate or in isografts.ConclusionsSarpogrelate hydrochloride may mitigate arteriosclerosis in allografts. Platelet aggregation and serotonin may be correlated with intimal thickening associated with chronic rejection.     

Beneficial effects of lexipafant, a PAF antagonist on gut barrier dysfunction caused by intestinal ischemia and reperfusion in rats

BACKGROUND: Platelet-activating factor (PAF) may play a pivotal role in the pathogenesis of intestinal ischemic injury. METHODS: The potential role of PAF in intestinal ischemia and reperfusion (I/R) and the development of gut endothelial and epithelial barrier dysfunction and distant organ injury were investigated by pretreatment with a PAF antagonist, lexipafant. Bidirectional permeability of the intestinal barrier, enteric bacterial translocation, protease-antiprotease balance and mucosal histology, and also changes in pulmonary and liver endothelial barrier permeability were measured following intestinal ischemia for 40 min with 6 h of reperfusion in rats. RESULTS: Intestinal mucosal endothelial and epithelial permeabilities significantly increased in animals with I/R. Lexipafant prevented the increase in albumin leakage from blood to the mucosal interstitium and the intestinal lumen during reperfusion, and the mucosal albumin leakage from the gut lumen to blood during I/R. Bacterial translocation was frequently noted in animals with I/R, while only a few positive cultures were obtained in animals with I/R administered lexipafant. Less leakage of fluorescein isothiocyanate dextran 70,000 into the interstitial space and gut lumen in I/R animals with lexipafant pretreatment was found under fluorescein microscopy. Lexipafant also partly prevented C1 inhibitor, prekallikrein, and factor X consumption in I/R animals and partly prevented changes in pulmonary and liver albumin leakage. CONCLUSIONS: PAF seems to play an important role in I/R-associated intestinal dysfunction and the development of distant organ dysfunction, probably by triggering endothelial and epithelial barrier dysfunction. Furthermore, PAF seems to be partly involved in activation of the protease-antiprotease system. The use of PAF antagonists may provide a mode of treatment against I/R-associated organ dysfunction.     

The course of pancreas allografts in rats conditioned by spleen allografts.

A new technique for transplanting duct-ligated rat pancreas grafts, rather similar to the technique for spleen grafting in rats, is presented. Inbred AGUS and WAG rats with a strong Ag-B incompatibility were used. Duct-ligated pancreas AGUS to AGUS isografts survived indefinitely in streptozotocin-induced diabetic hosts while WAG to AGUS allografts were quickly rejected. However, when WAG spleen and pancreas were transplanted en bloc to AGUS rats, endocrine pancreas graft function persisted for up to 6 weeks. This finding of a transient protection of pancreas allografts by donor-strain spleen allografts led to further experiments. AGUS recipients first received WAG spleen allografts which then were removed after 3 to 5 months, at which time WAG pancreas allografts were inserted. Sixty-eight per cent of these grafts survived and cured their hosts of streptozotocin-induced diabetes.     

31P nuclear magnetic resonance of rat pancreatic grafts

This study investigates whether phosphate metabolite concentrations and intracellular pH alter in early acute rejection of rat pancreatic allografts. In vitro biochemical assays, in vitro 31P nuclear magnetic resonance spectroscopy, and in vivo 31P NMR spectroscopy of the grafts were compared. Duct-ligated, vascularized rat pancreatic isografts and allografts were transplanted onto the infrarenal aorta of the recipients with inferior vena cava venous drainage. In order to obtain reproducible acute rejection, allografting was performed across a major histocompatibility barrier. For the in vitro experiments freeze-clamped graft extracts were prepared and analyzed for adenosine triphosphate concentration by fluorimetry, then placed in an 8.5 Tesla vertical bore magnet. 31P NMR spectra were recorded using a Bruker AM 360 spectrometer operating at 145.7 MHz for 31P. Spectra were acquired from nontransplanted controls; 3-day, 5-day, and 1-month posttransplant isografts, and 3-day and 5-day posttransplant allografts. All grafts examined were functioning satisfactorily. The ATP content of the extracts was significantly lower in the 3- and 5-day allografts than the respective isografts. Invasive in vivo 31P NMR spectra were recorded using surface coils adjacent to the grafts from functioning 5-day posttransplant isografts and allografts (i.e., 3 days prior to an expected elevation in blood sugar from acute rejection in the allografts). The ATP/inorganic phosphate ratios and pH from the in vivo spectra were significantly lower in the allografts than in the isografts. It is concluded that changes in intracellular metabolism occur early in the process of acute rejection and that 31P NMR spectroscopy may provide a means of diagnosing this before current methods.     

Increased risk of antibody-mediated rejection of reduced-size liver allografts

Because of the shortage of liver allografts in children, transplantation of reduced-size liver allografts from adult cadaveric donors or living, related donors is being done more frequently. Reduced-size liver allografts may be used in cases of ABO incompatibility and T-cell warm cross-match positivity. This experimental study in inbred rats was undertaken to determine if reduced-size liver allografts are more sensitive to antibody-mediated rejection than full-size liver allografts. Brown-Norway (BN) (RT1(n)) rats were sensitized by three successive skin grafts at 10-day intervals. Then orthotopic Lewis (LEW) (RT1(1)) liver grafts were transplanted into these BN rats. Full-size liver allografts were compared with reduced-size liver allografts (70% of donor liver). Control groups were composed of full-size and/or reduced-size isografts. Titers of specific antibodies were assayed using a complement-dependent assay before and after orthotopic liver transplantation. Histological and immunofluorescence studies (IgG, IgM, C(3), and fibrinogen deposits) were assessed. Recipients of reduced-size liver allografts died of hyperacute rejection at 36.6 +/- 4.1 h, significantly earlier than recipients receiving full-size liver allografts, which died of accelerated acute rejection at 259.2 +/- 25.2 h (P < 0.001). Either full-size or reduced-size isograft recipients survived indefinitely. A decrease in the titers of donor-specific antibodies was observed in both groups of animals. Slight deposits of IgG, IgM, C(3), and fibrinogen were observed in recipients of reduced-size liver allografts, whereas larger deposits were observed in recipients of full-size liver allografts. Our data demonstrate that there is an increased risk of antibody-mediated rejection of reduced-size liver allografts in sensitized recipients. This may have important clinical implications for partial liver grafting in cases of ABO incompatibility and T-cell warm cross-match positivity.     

Changes in myocardial beta-adrenergic receptors during acute rejection of heterotopically transplanted rat hearts.

To evaluate changes of the myocardial beta-adrenergic receptors in acute cardiac graft rejection, the density and binding affinity value of the myocardial beta-adrenergic receptors in heterotopically transplanted rat isografts and allografts were analyzed. Hearts from Fisher rat donors were transplanted either to the Fisher rats (isografts) or to Lewis rats (allografts). Histologic examination of the allografts showed mild to moderate rejection on the seventh and fourteenth days and showed severe rejection on the twenty-first day after transplantation. The density values in the allografts and isografts similarly increased significantly (p < 0.05) above the normal level on the seventh and fourteenth days after transplantation. The density in allografts on the twenty-first day decreased significantly (p < 0.05) below the normal level, while that in isografts remained at the normal level. In contrast, the binding affinity value of myocardial beta-adrenergic receptors in both isografts and allografts did not change after transplantation. These results demonstrated that myocardial beta-adrenergic receptors presented upregulation in mild to moderate rejection, whereas these receptors presented downregulation in severe rejection. The data suggested that downregulation of myocardial beta-adrenergic receptors plays a major role in decreased cardiac contractility during severe rejection, but not during mild and moderate rejection.     

A novel model of portal vein transplantation in mice using two-cuff technique

Allogeneic portal vein (PV) grafts have been widely used for vascular reconstruction in the aggressive biliary-pancreatic surgery and partial liver transplantation. We developed a novel PV transplantation model aimed at studying the pathologic alteration of the grafts and further managements. The PV graft was implanted orthotopically into the recipient using two-cuff technique. A total of 80 PV transplants have been performed, and the overall survival rate for the recipients was 91.3% (73/80). Mice were randomly separated into isografts group, allografts group, and allografts group treated with CTLA4-Ig. PV grafts were harvested on the 1st, 2nd, 4th, and 8th postoperative week. The isografts remained intact vascular structure, and the allografts developed marked rejection with significant increase in wall thickness (95 +/- 19 microm vs. 49 +/- 7 microm; P < 0.01) and decrease in lumen area (1.9 +/- 1.1 x 10(4) microm(2) vs. 7.7 +/- 3.1 x 10(4) microm(2); P < 0.01) on the 4th week. In the CTLA4-Ig treated group, the vascular thickness and lumen area were significantly improved when compared with the untreated allografts (wall-thickness: 53 +/- 3 microm vs. 95 +/- 19 microm, P < 0.01; lumen area: 8.8 +/- 2.4 x 10(4) microm(2) vs. 1.9 +/- 1.1 x 10(4) microm(2), P < 0.01) on the 4th week. In conclusion, the PV transplantation model in mice using two-cuff technique is a feasible procedure with a high survival rate. The PV allografts responded well to the CTLA4-Ig therapy in our preliminary research by the model.     

Role of bacterial adherence and the mucus barrier on bacterial translocation: effects of protein malnutrition and endotoxin in rats.

OBJECTIVE: The purpose of the study was to investigate the potential relations between mucosal bacterial adherence, intestinal mucus and mucin content, and bacterial translocation. SUMMARY BACKGROUND DATA: The attachment of bacteria to mucosal surfaces is the initial event in the pathogenesis of most bacterial infections that originate at mucosal surfaces, such as the gut. The intestinal mucus layer appears to function as a defensive barrier limiting micro-organisms present in the intestinal lumen from colonizing enterocytes. Consequently, studies focusing on the biology of bacterial adherence to the intestinal mucosa likely are to be important in clarifying the pathogenesis of gut origin sepsis. METHODS: To explore the relations between intestinal bacterial adherence, mucus bacterial binding, and bacterial translocation, two models were used. One (protein malnutrition) in which profound alterations in intestinal morphology occurs in the absence of significant translocation and one (endotoxin challenge) in which bacterial translocation occurs and intestinal morphology is relatively normal. RESULTS: Protein malnutrition was not associated with bacterial translocation and measurement of enteroadherent, mucosally associated bacterial population levels documented that the total number of gram-negative enteric bacilli adherent to the ileum and cecum was less in the protein-malnourished rats than in the normally nourished animals (p < 0.01). Furthermore, there was an inverse relation between the duration of protein malnutrition and bacterial adherence to the intestinal mucosa (r = 0.62, p < 0.002). In contrast, after endotoxin challenge, the level of enteroadherent bacteria was increased and bacterial translocation was observed. The binding of Escherichia coli to immobilized ileal mucus in vitro was decreased significantly in protein-malnourished rats, whereas E. coli binding to insoluble ileal mucus was increased in the rats receiving endotoxin. CONCLUSIONS: This study indicates that the adherence of bacteria to the intestinal mucosal surface is an important factor in bacterial translocation, that intestinal mucus modulates bacterial adherence, and that increased levels of mucosally associated bacteria are associated with a loss intestinal barrier function to bacteria.     

银杏叶提取物预处理对胰腺移植受体大鼠 小肠肠黏膜屏障的影响

目的 ：探讨银杏叶提取物（EGb）对胰腺移植受体大鼠肠黏膜屏障的保护作用及其机制。方法 ：12只正常SD大鼠为对照组;糖尿病大鼠随机分为胰腺移植组（PT组， n =12）及银杏叶提取物预处理胰腺移植组（EGb组， n =12），大鼠均接受同系胰腺移植。EGb组于移植前1d和30min予受体静脉注射EGb （1.5mL/kg）。移植术后5 d测定小肠通透性和吸收功能，检测血清TNF-α，NO，SOD和淀粉酶活性。取受体回肠黏膜组织测定小肠黏膜湿重、微绒毛厚度及宽度、MDA含量及MPO活性。同时取肠系膜静脉血、肠系膜淋巴结、肝及脾组织行细菌培养，观察细菌易位情况。结果 ：EGb组血清TNF-α含量（ P <0.01）、淀粉酶活性（ P <0.01）、MDA含量（ P <0.05）、MPO活性（ P <0.05）、小肠通透性（ P <0.01）、细菌易位率（ P <0.01）和小肠黏膜损伤程度均低于PT组;血清NO和SOD含量、小肠吸收功能均高于PT组( P <0.01)。结论 ：EGb预处理可保护胰腺移植受体大鼠小肠肠黏膜屏障，降低细菌易位率，机制可能与抗氧化、清除自由基、减少TNF-α生成、减轻嗜中性粒细胞黏附与聚集、增加内源性NO的生成有关。     

Experimental vascularized bone allografting

Presented here is a compendium of studies investigating the fate of vascularized bone allografts. The first set of experiments employ the posterior rib graft in two canine models. The rib-to-mandible model was used to evaluate the rejection phenomena of vascularized bone allografts in an outbred dog model. This ascertained the time course of rejection and histological characteristics of the grafts. Immunosuppression of the graft recipients was attempted with azathioprine and cyclosporine. The results demonstrated that azathioprine was not an effective immunosuppressant, whereas cyclosporine resulted in survival of cortical osteons. The use of the vascularized rib allograft, with and without azathioprine, to bridge the defect in the dog femur was met with failure. Further studies employed a genetically defined rat model to determine the effect of different histocompatibilities on the survival of vascularized knee allografts. Grafts were transplanted from Lewis rats to syngeneic Lewis rats as isografts and to Fischer-344 rats (F-344) and Brown-Norway rats (BN) as allografts. Grafts across a major histocompatibility barrier to BN were rejected by 7 days, whereas grafts across a weak histocompatibility barrier to F-344 were rejected more slowly. The use of cyclosporine in this model abrogated the rejection response when administered to both groups continuously. However, a short course of cyclosporine was effective in preventing rejection in the F-344 animals. Efforts to induce tolerance by blood transfusions, from the donor strain or from a third-party donor, were not effective in preventing rejection.     

Characterization of allograft rejection in an experimental model of small intestinal transplantation

Graft rejection continues to be a major barrier to the success of clinical small intestinal transplantation. The objective of this study was to characterize histopathologic and immune parameters of allograft rejection in an experimental model of small intestinal transplantation. Heterotopic intestinal transplants were performed in allogeneic and isogeneic rat strain combinations. An additional group of allogeneic recipients was treated with tacrolimus (1 mg/kg/day) for 7 days beginning on posttransplant day 1. Recipients of allografts and isografts were killed on days 1 to 7 following transplantation, and tacrolimustreated allograft recipients were killed on days 4 and 7. Grafts and native intestines were examined for histopathology and cytokine gene expression. Very early rejection was observed on posttransplant day 3 and severe rejection was apparent by day 7. The key histopathologic features of acute graft rejection including apoptosis, crypt epithelial cell injury, and an inflammatory infiltrate were uniformly identifiable on day 4 and progressed in severity through day 7. Interleukin (IL)-2, IL-4, IL-5, IL-6, interferon-γ (IFN-γ), and tumor necrosis factor-γ mRNA were readily detectable in allografts on days 1 to 7. However, only IFN-γmRNA showed a significant early and sustained increase in allografts as compared to isografts and native intestine. Treatment of allograft recipients with tacrolimus abrogated the major histopathologic features of rejection and markedly inhibited IFN-γgene expression. These results indicate that graft rejection in small intestinal transplantation is characterized by a local and specific immune response marked by WN-γproduction that results in crypt epithelial cell injury and apoptosis. Tacrolimus abrogates the histopathologic features of rejection in association with a marked inhibition of IFN-γgene expression. Supported by grants from the Lucile Packard Foundation and the Office of Technology and Licensing, Stanford University