It has been demonstrated that patients with asthma have a large number of NK cells and show a stronger NK activity. These results indicate that NK cell activity may be related to total IgE level in serum in healthy subjects. Previously,we have found that sodium butyrate (NaBu) markedly enhanced the IL- 4- induced IgE production in the LPS- stimulated murine splenocytes in vitro, and inductive rat IgE production in vivo, and enhanced the NK cell activity ex vivo .We hypothesized that the IgE production might be involved in butyrate- enhanced NK cell activity in vivo. Mice were intraperitoneally treated/immunized with NaBu or/and Ascaris suum extract (ASC),and the spleen NK cell activity was evaluated. Furthermore, the effect of serum (NAS) on IL- 2- or IFN-γ- induced spleen NK cell activity was determined. The spleen NK cell activity and IL- 2- or IFN-γ- induced spleen NK cell activity of mice treated/immunized with NaBu or/and ASC were stronger than those of untreated/unimmunized mice. Although IL- 4 blocked IL- 2 (100 U/ml)- or IFN-γ (100 U/ml)- induced increase in NK cell activity,these NK cell activities in mice treated/immunized with NaBu/ASC were not inhibited. IgE production showed a tendency to rise in NaBu- treated mice serum, and a synergistic effect was observed with treatment of NaBu and ASC. Moreover, the NAS significantly increased IL- 2(25 U/ml)- or IFN-γ (25 U/ml)- induced NK cell activity, and its effect was inhibited by anti- mouse IgE mAb. These data show that IgE plays an important role in NAS- enhanced IL- 2/IFN-γ- induced NK cell activity, and IL- 4 does not inhibit IgE and IL- 2/IFN-γ- induced NK cell activity in mice. It has been demonstrated that patients with asthma have a large number of NK cells and show a stronger NK activity. These results indicate that NK cell activity may be related to total IgE level in serum in healthy subjects. Previously, we have found that sodium butyrate (NaBu) markedly enhanced the IL-4-induced IgE production in the LPS-stimulated murine splenocytes in vitro, and inductive rat IgE production in vivo, and enhanced the NK cell activity ex vivo. We hypothesized that the IgE production might be involved in butyrate-enhanced NK cell activity in vivo. Mice were intraperitoneally treated / immunized with NaBu and / and Ascaris suum extract (ASC), and the spleen NK cell activity was evaluated. Furthermore, the effect of serum (NAS) on IL- 2- or IFN-γ-induced spleen NK cell activity was determined. The spleen NK cell activity and IL-2- or IFN-γ-induced spleen NK cell activity of mice treated / immunized with NaBu or / and ASC were stronger than those of untreated / unimmunized These NK cell activities in mice treated / immunized with NaBu / ASC were not induced by IL-4 blocked IL-2 (100 U / ml) - or IFN- γ inhibited. IgE production showed a tendency to rise in NaBu-treated mice serum, and a synergistic effect was observed with treatment of NaBu and ASC. Moreover, the NAS significantly increased IL-2 (25 U / ml) 25 U / ml) - induced NK cell activity, and its effect was inhibited by anti-mouse IgE mAb. These data show that IgE plays an important role in NAS-enhanced IL- 2 / IFN- γ-induced NK cell activity, and IL-4 does not inhibit IgE and IL-2 / IFN-γ-induced NK cell activity in mice.