Murine macrophage cell line J774A.1 (ATCC no. TIB-67) was maintained in phenol red free DMEM supplemented with 10% heat inactivated (45 min at 65°C) foetal bovine serum at 37°C in 5% C02 and 95% air. The cultures were sub-cultured every three days or at the attainment of 80 % confluency.