Modulation of natural killer cell activity in mice after interferon induction: depression of activity and depression of in vitro enhancement by interferon.

Splenic natural killer (NK) cell activity of BALB/c and C3H mice was assayed after administration of the interferon inducers Escherichia coli endotoxin or Newcastle disease virus (NDV). As expected, the NK cell activity rose early in response to the interferon inducers. At 1 to 3 days after an injection of endotoxin, NK activity was hyperesponsive to interferon stimulation. At 5 to 9 days after injection of either endotoxin or NDV, splenic NK activity was depressed, and the spleen cells showed a relative refractoriness to in vitro interferon stimulation. It is postulated that this phenomenon may be related to hyporeactivity, the inability to reinduce interferon after an initial period of interferon production.