Augmentation of natural killer cell activity by ImuVert: a biological response modifier derived from Serratia marcescens.

The natural killer (NK) cell activity of peripheral blood mononuclear cells (PBMC) from healthy human volunteers was studied following in vitro incubation with ImuVert, a biological response modifier derived from the bacterium Serratia marcescens. Exposure of these cells to ImuVert for as little as 10 minutes followed by an additional incubation in vitro of at least 12 hours and optimally 18 hours resulted in a substantial, consistent, and dose-dependent augmentation of NK cell activity against K562 tumor cells. Additional studies indicate that the augmented cell expressed the leu 11 cell surface marker and that peripheral blood monocytes were essential in the induction of augmented NK cell activity but were not the effector cell of NK activity.