FOLLOW-UP-STUDY OF THE REVASCULARIZATION PROCESS OF PURIFIED RAT ISLET BETA-CELL GRAFTS

The revascularization of islets of Langerhans transplanted in heteroto pic sites like the liver by portal vein embolization or the renal subc apsular space is a major process necessary for the viability of grafte d cells. This process has been extensively studied by different techni ques and the results have shown that islet revascularization is an ear ly phenomenon that takes place soon after transplantation. In this rep ort we have analyzed by a double indirect immunofluorescence technique , the revascularization process of purified endocrine islet beta-cells transplanted in the renal subcapsular space of syngeneic rats. Lewis rats were grafted with islets cultured for 24 h, with a suspension of purified beta-cells cultured for 24 h, and with a suspension of purifi ed beta plus nonbeta-cells cultured for 24 h. Rats were killed at diff erent days after implantation and the kidney bearing the grafts were s nap frozen and immunohistochemically stained with a rabbit anti factor VIII antiserum (which labels endothelial cells). Immunocytochemical a nalysis revealed that cultured islets completed revascularization by d ays 3-5 after transplantation, as shown by the detection of capillary endothelial cells within and surrounding the islets. Within purified e ndocrine beta-cell grafts, the presence of numerous endothelial cells was not observed until days 10-14, indicating that revascularization o f beta-cells with host vessels is not such an early phenomenon as it t akes place in whole isolated islets. Conversely, the addition of a pop ulation of endocrine nonbeta-cells to the purified islet cell grafts, partially accelerated the revascularization of pure beta-cell grafts, which showed the presence of abundant capillary endothelial cells alre ady at day 7 after transplantation, indicating that some other unident ified factors besides the absence of endothelial cells may explain the retardation of beta-cell grafts revascularization. (C) 1997 Elsevier Science Inc.