Interferon production by mitogen-stimulated human lymphocytes requires differentiation but not DNA synthesis

Mitogens such as phytohemagglutinin (PHA) stimulate T lymphocytes to differentiate, proliferate, and produce lymphokines: e.g., interferon gamma (IFN gamma) and interleukin-2 (IL-2). Induction of IFN gamma is an early event in mitogenesis, accompanied by an increase in RNA and protein synthesis, and later followed by DNA synthesis. Although, in general, good IFN gamma inducers are good mitogens, we show here that DNA synthesis is not an obligatory requirement for the production of IFN gamma. Aphidicolin and hydroxyurea, which completely inhibit DNA synthesis, do not significantly affect IFN production, whether added before, with, or after mitogen stimulation. Inhibitors of differentiation, however, affect DNA and IFN synthesis depending on their time of addition in relation to PHA. The inhibitors, 3-methoxybenzamide (3MB) and a group of compounds that affect cyclic nucleotide metabolism (theophylline, aminophylline, and dibutyryl cyclic AMP), had profound inhibitory effects on IFN production. However, bromodeoxyuridine (BUdR), also an inhibitor of differentiation in some systems, had very little effect on IFN production.