IMMORTALIZATION AND CHARACTERIZATION OF RAT MICROGLIAL CELLS

Microglial cell lines from rat brain were established by transfer of a temperature sensitive simian virus 40 large tumour antigen by means o f a retrovirus. Four weeks after infection, colonies were generated in the presence of neomycin and granulocyte-macrophage colony stimulatin g factor (GM-CSF), and subsequently subcloned. Both bulk cell lines an d clones proliferate actively at 33 degrees C, whereas the rate of div ision was significantly decreased at 39 degrees C when the large T ant igen is non-functional. At 39 degrees C, these cells take on the micro glial phenotype as demonstrated by immunoreactivity to ED-1 (an intrac ellular antigen), OX-42 (complement type 3 receptor), W3/25 (CD4 homol ogue), OX-6 (MHC class II antigen) and OX-18 (MHC class I antigen). Th ese cells are capable of active phagocytosis and retain these properti es for 10-15 passages. Long-term culture of these lines and clones, gr eater than 15 passages, displayed a gradual down-regulation of all cel l surface specific antigens that were not rescued by lipopolysaccharid e (LPS), interferon-gamma (gamma-IFN), GM-CSF or colony-stimulating fa ctor-1 (CSF-1). The expression of the SV-40 large T antigen was unaffe cted. These results demonstrate the feasibility of immortalizing short -term cell lines with the SV-40 large T antigen for their use in the c haracterization of microglial properties.