Quantitative analysis of the cooperative effect between inducers of Epstein-Barr virus antigen synthesis.

Induction of Epstein-Barr virus antigens in Raji cells by 12-O-tetradecanoylphorbol 13-acetate (TPA), 5'-iodo-2'-deoxyuridine (IUdR), n-butyric acid (n-BA) antibody to IgM (anti-IgM) and a recently described serum factor was studied after single applications of individual inducers or of their combinations. Whereas individual inducers led to activation only in a limited number of cells, certain combinations of inducers greatly enlarged the reactive cell population. In synergistically acting combinations of drugs, the dose necessary for half-maximal induction of the first inducer was shifted to a much lower value by the second inducer. The serum factor cooperated with any of the four inducers TPA, IUdR, anti-IgM and n-butyric acid, whereas TPA only interacted with IUdR and n-butyric acid. The effects of the serum factor and of TPA showed some similarities but were not identical, whereas IUdR and n-BA showed identical effects.