Rat astrocytic tumour cells are associated with an anti-inflammatory microglial phenotype in an organotypic model

Aim: Microglia form a high proportion of cells in glial tumours but their role in supporting or inhibiting tumour growth is unclear. Here we describe the establishment of an in vitro model to investigate their role in astrocytomas. Methods: Rat hippocampal slices were prepared and, after 7 days to allow microglia to become quiescent, rat C6 astrocytic tumour cells were added. Over the following 7 days, infiltration and cell death were studied using fluorescent C6 tumour cells and confocal microscopy; immunophenotyping of microglia was performed using CD68 (phagocytosis), MHCII (antigen-presentation) and Iba1 (microglial marker regardless of functional state). Cell proliferation was assessed using Ki67 and qPCR to detect cytokine expression. Sham and control groups were included. Results: Microscopy showed proliferation of C6 tumour cells with both infiltration of tumour cells into the hippocampal tissue and of microglia amongst the tumour cells. Confocal experiments confirmed increasing tumour cell infiltration into the hippocampal slice with time (P Conclusion: This model allows study of the proliferation and infiltration of astrocytic tumour cells in CNS tissue and their interaction with microglia. Our data suggest that microglial function is altered in the presence of tumour cells, putatively facilitating tumour progression. Manipulation of the microglial functional state may have therapeutic value for astrocytic tumours.