Effects of cimetidine on various biological activities of human leucocyte interferon and on interferon production in lymphocytes.

In vitro effects of cimetidine on the antiviral, the antiproliferative and the natural killer (NK) cell stimulating activities of human leucocyte interferon (IFN-alpha (Le], and on the Sendai virus induced interferon production in lymphocytes were investigated. The antiviral activity of IFN-alpha (Le) was dosedependently enhanced by cimetidine, which alone did not demonstrate any antiviral action. The observed titer of the same IFN preparation titrated with 60 micrograms/ml of cimetidine was significantly higher (p less than 0.05) than that without cimetidine. Cimetidine slightly but dosedependently inhibited the growth of Daudi or G-361 cells. The combination effects of these two agents were revealed to be statistically additive or synergistic. The NK cell activity of peripheral blood lymphocytes (PBL) was suppressed after a 16 hr pretreatment with cimetidine. Furthermore, the interferon production in normal lymphocyte cultures was suppressed dosedependently by cimetidine. On the other hand, the augmentation of the NK cell activity by interferon was further potentiated by cimetidine.