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.