Murine macrophage RAW 264.7 cells (ATCC TIB-71) were maintained in RPMI 1640 media (Gibco BRL), supplemented with 2 mM L-glutamine (Gibco BRL), 10% serum supreme (BioWhittaker), 200 µg/ml penicillin, 100 µg/ml streptomycin, 25 mM N-2-hydroxyethylpiperazine-N-2-ethane sulphonic acid (HEPES) and 25 mM sodium bicarbonate, in 5% CO2 and 95% humidified air atmosphere at 37°C. Wild-type (Cebpb+/+) and knockout (Cebpb−/−) mouse embryonic fibroblasts (MEFs) [34] were grown in Dulbecco's modified Eagle's medium (Invitrogen) supplemented with 10% fetal bovine serum and 1% penicillin/streptomycin/glutamate solution (Cellgro).