Follow-up study of the revascularization process of purified rat islet beta-cell grafts

The revascularization of islets of Langerhans transplanted in heterotopic sites like the liver by portal vein embolization or the renal subcapsular space is a major process necessary for the viability of grafted cells. This process has been extensively studied by different techniques and the results have shown that islet revascularization is an early phenomenon that takes place soon after transplantation. In this report 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 purified beta plus nonbeta-cells cultured for 24 h. Rats were killed at different days after implantation and the kidney bearing the grafts were snap frozen and immunohistochemically stained with a rabbit anti factor VIII antiserum (which labels endothelial cells). Immunocytochemical analysis revealed that cultured islets completed revascularization by days 3-5 after transplantation, as shown by the detection of capillary endothelial cells within and surrounding the islets. Within purified endocrine beta-cell grafts, the presence of numerous endothelial cells was not observed until days 10-14, indicating that revascularization of beta-cells with host vessels is not such an early phenomenon as it takes place in whole isolated islets. Conversely, the addition of a population 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 already at day 7 after transplantation, indicating that some other unidentified factors besides the absence of endothelial cells may explain the retardation of beta-cell grafts revascularization.