Although the involvement of complement in hyperacute rejection of xenotransplants is well recognized, its role in rejection of devascularized xenografts, such as pancreatic islets, is not completely understood. In this study, we investigated whether complement participates in the immunopathology of xeno-islet transplantation in a concordant rat to mouse model. Rat pancreatic islets were implanted under the kidney capsule of normal and cobra venom factor (CVF) decomplementized diabetic C57BL/6 mice. Graft survival was monitored by blood glucose levels. Deposition of IgM and C3 on grafted islets in vivo or on isolated islets in vitro (after incubation with normal and decomplementized mouse serum), as well as CD4-and CD8-positive leucocyte infiltration of grafts, was checked by immunohistochemistry. In addition, complement-mediated cytotoxicity on rat islet cells was evaluated by a 3-(4, 5-dimethythiazolyl)-2. 5-diphenyl-2Htetrazolium bromide (MTT) assay. A significant C3 deposition was found on grafted islets from the first day after transplantation in vivo, as well as on isolated islets after incubation with mouse serum in vitro. By MTT assay, complement-mediated cytotoxicity for islet cells was found. Decomplementation by CVF decreased C3 deposition on either isolated or grafted islets, delayed CD4-and CD8-positive leucocyte infiltration, led to significant inhibition of complement-mediated cytotoxicity for islet cells, and prolonged graft survival (mean survival time 21•3 versus 8•5 days; P<0•01). Our results indicate that decomplementation can prolong the survival time of devascularized xenografts across concordant species. The deposition of complement on transplanted islets may contribute to xenograft rejection by direct cytotoxicity and by promoting leucocyte infiltration.

There is a microcirculation system within the islets of Langerhans. However, little is known about the phenotypicand functional characterization of islet microvascular endothelial cells (MVEC). In this study, we purified MVEC from human pancreatic islets by using Ulex europaeus(Sigma, St. Louis, MO)agglutinin-1(UEA-1)-coated dynabeads(Dynal A. S., Oslo, Norway). These purified human islet MVEC (HI-MVEC) express von Willebrand factor, take up high levels of acetylated LDL, and upregulate endothelial cell leukocyte adhesion molecule 1 in response to tumor necrosis factor-a. Ultrastructure examination shows the presence of microvilli and fenestrations on the cell surface, Weibel-Palade bodies in the cytoplasm, and tight junctions between cells. Furthermore, we show that vascular endothelial cell growth factor contributes to the formation of surface fenestrations on cultured HI-MVEC. After purification, HI-MVEC exhibit a very low proliferation capacity and are strongly resistant to trypsin, compared with other original MVEC. We also demonstrate that a-1 proteinase inhibitor(Api)is expressed on HI-MVEC and specifically located at the area of cell-cell junctions. By reverse transcription-polymerase chain reaction, a significant messenger RNA band of Api was found only in HI-MVEC, but not in other organ-derived MVEC, indicating that expression of Api is islet MVEC specific. Antibodies to Api significantly reversed the resistance to trypsin and promoted proliferation of HI-MVEC, suggesting that these specific functional characteristics of HI-MVEC are related to the expression of Api. These results indicate that HI-MVEC exhibit some specific morphological and functional characteristics that differ from MVEC derived from other organs. Diabetes 48: 1773-1778, 1999

Xenogeneic islets could provide an unlimited source of tissue for the treatment of diabetes, and could in theory be transplanted repeatedly in a recipient. However, little is known on the consequences of islet re-transplantation in a recipient who has rejected a

采用腹腔内1次注射60mg/kg体重STZ方法，建立了速发型链脲佐菌素Wistar大鼠糖尿病模型。采用每周1次连续3周腹腔内注射CFA 0.5ml和STZ（25mg/kg）方法，建立了迟发型Wistar大鼠糖尿病模型。结果提示：速发型模型建立的机制与STZ直接损伤胰岛B细胞有关，迟发型大鼠糖尿病模型胰岛B细胞损伤可能与T淋巴细胞介导的免疫机制有关。

采用经胰导管连续灌注胶原酶技术，从每个胰腺中获得平均469100±208300个胰岛（7693个胰岛/g胰腺），纯化后平均152000±109000个胰岛/胰腺（2486个胰岛/g胰腺）。平均回收率32.49%，纯度80%。在培养第1、第3和第7天间，胰岛细胞对高糖和茶碱刺激有明显反应，胰岛素释放量，分别为低糖的1.39～3.67（P<0.05），提示分离纯化后及培养期间的胰岛功能良好。胰岛形态学观察表明，双硫腙特异性的与胰岛B细胞胰岛素颗粒内的锌螯合使其着色，台盼兰染色证实胰岛活率在90%以上。本文将分离纯化后及培养的经双硫腙染色的阳性细胞团进行电镜检查，证实为形态结构完整的胰岛。