Mouse fibroblast (L929) was cultured in RPMI1640 medium
supplemented with 10% fetal bovine serum, together with 1.0%
penicillin-streptomycin, and 1.2% glutamine. Culture was maintained
at 37 ◦C in a wet atmosphere containing 5% CO2. When the
cells reached 80% confluence, they were trypsinized with 0.25%
trypsin containing 1 mM ethylenediamine tetraacetic acid (EDTA).