COLONIZATION OF NEURAL ALLOGRAFTS BY HOST MICROGLIAL CELLS - RELATIONSHIP TO GRAFT NEOVASCULARIZATION

In order to illuminate functional roles of microglial cells within neu ral allografts, we have transplanted both whole and microglial and end othelial cell-depleted E14 neural cell suspensions into the intact str iatum of Sprague-Dawley rats, Following posttransplantation times of u p to 30 days, the intrastrial allografts were analyzed histochemically using the Griffoilia simplicifolia B-4 isolectin, a marker for both m icroglia and blood vessels, Our results indicate that both whole and d epleted suspension grafts develop identically in terms of neovasculari zation and microglial colonization, In both types of transplants micro glial cells appeared before any blood vessels were apparent, The main phase of graft vascularization occurred between days 7 and 10 posttran splantation and neovascularization was complete by day 21, as revealed by quantitative image analysis, Microglial cells, which were present as ameboid cells during early posttransplantation times, underwent con tinuing cell differentiation with time that paralleled graft vascular development, By 30 days posttransplantation microglia within the graft s had assumed the fully ramified phenotype characteristic of resting a dult microglia, During graft development and vascularization, microgli a were often seen in close proximity to ingrowing blood vessels and va scular sprouts, In conclusion, our study has shown that microglial col onization of grafts and graft vascularization occurs independent of do nor-derived microglial and endothelial cells, and suggests that the gr eat majority of microglia and vessels within the graft are host derive d, We hypothesize that the host microglia invading the allografts play an active role in promoting graft neovascularization. (C) 1997 Elsevi er Science Inc.