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). Primary peritoneal macrophages were obtained by injecting C57BL/6 mice with 3% thioglycollate broth followed by peritoneal lavage 3–5 days later, and maintained in 50% DMEM/F12 media (Gibco BRL). Precautions were taken to exclude bacterial lipopolysaccharide contamination from all cell cultures through the use of certified LPS-free serum. Cell viability was determined using the trypan blue (Sigma) dye exclusion method. All cultures were routinely checked to exclude Mycoplasma infection by nuclear staining using Hoechst stain 33258 (Sigma) and the MycoAlert Detection Kit (Lonza). Bacterial lipopolysaccharide (LPS) (Salmonella minnesota Strain Re595) was obtained from Sigma.