Solutions were sterilized by filtration through 0.2 m pore-size filters (Machery-Nagel, D en, Germany). Stock solutions of 100 g/ml recombinant murine IFN- (HyCult biotechnology, Uden, The Netherlands) and 1 mg/ml recombinant murine IFN- (PeproTech, Rocky Hill, NJ, USA) were made in medium. Neutralizing mAb, originally obtained from Dr. Brahic (Institut Pasteur, Paris, France), was diluted in medi