Aim:To investigate the immunoregulatory functions of water extracts of Hericiumerinaceum (WEHE) focusing on natural killer (NK) cell-based anticancer activities.Methods:Mouse splenocytes or purely isolated NK ceils were stimulated with1-100 mg/L WEHE for 24 h followed by co-culture with ~(51)Cr-labled Yac-1 cells for4 h,then NK cell-derived cytolytic activity was measured using a radio-releaseassay.Neutralizing antibodies against mouse interleukin-12 (IL-12) were addedinto the WEHE-stimulated splenocytes,thereafter,cytotoxicity was measured toexamine the involvement of IL-12.RT-PCR and ELISA analyses were performed toconfirm the induction of transcription and the translation of IL-12 and interferon-gamma (IFN-gamma) in the WEHE-treated splenocytes.Results:WEHE enhancedthe cytolytic activity of total splenocytes towards Yac-1 ceils in a dose-dependentmanner.However,this activation was not observed when the NK cells isolatedfrom the splenocytes were treated with WEHE.Furthermore,the treatment withantibodies against IL-12 abolished the effect of WEHE on splenocyte-derivedcytolytic activity.RT-PCR and ELISA analyses showed the induction of IL-12 andIFN-gamma in the WEHE-treated splenocytes.Conclusion:WEHE indirectlyactivates the cytolytic ability of NK cells via the induction of IL-12 in totalsplenocytes,and possibly via other immuno-mediators or cellular components. Aim: To investigate the immunoregulatory functions of water extracts of Hericiumerinaceum (WEHE) focusing on natural killer (NK) cell-based anticancer activities. Methods: Mouse splenocytes or purely isolated NK ceils were stimulated with 1 to 100 mg / L WEHE for 24 h followed by co-culture with ~ (51) Cr-labled Yac-1 cells for 4 h, then NK cell-derived cytolytic activity was measured using a radio-releaseassay. Neutralizing antibodies against mouse interleukin-12 -stimulated splenocytes, thereafter, cytotoxicity was measured toexamine the involvement of IL-12.RT-PCR and ELISA analyzes were performed toconfirm the induction of transcription and the translation of IL-12 and interferon-gamma (IFN-gamma) in the WEHE- treated splenocytes. Results: WEHE enhanced the cytolytic activity of total splenocytes towards Yac-1 ceils in a dose-dependentmanner. Host, this activation was not observed when the NK cells isolated from the splenocytes were treated with WEHE. Futurerther, the trea tment withantibodies against IL-12 abolished the effect of WEHE on splenocyte-derived cytolytic activity. RT-PCR and ELISA analyzes showed the induction of IL-12 and IFN-gamma in the WEHE-treated splenocytes. Confluence: WEHE-indirectly activated the cytolytic ability of NK cells via the induction of IL-12 in totalsplenocytes, and possibly via other immuno-mediators or cellular components.