The antiproliferative and differentiating effects of human leukemic U937 cells are mediated by cytokines from activated mononuclear cells by dietary mushrooms.

Proliferation of human leukemic U937 cells was remarkably inhibited by conditioned medium (CM) of human peripheral blood mononuclear cells (MNC-CM) stimulated with cold-water extracts (CWE) (10-800 microg/mL of medium) of dietary mushrooms, Hypsizigus mamoreus (HM), Agrocybe aegerita (AA), Flammulina velutipes (FV), whereas insignificant results were observed when cells were cultured in the presence of CWE at the corresponding level. Water extracts from mushrooms were fractionated by Sephadex G-50 chromatography, and the pooled high molecular weight fraction (F1) (200 microg/mL) of HM (HM1) and AA (AA1) exhibited growth inhibitions >80% on U937 cells. Interestingly, the thus-cultured U937 cells showed high nitroblue tetrazolium (NBT) positive (>68%) and nonspecific esterase (NSE) positive (>47%) percentages, revealing the remarkable differentiation into monocytes/macrophages upon incubation with HM1- and AA1-stimulated MNC-CM. In addition, assays for the expressions of monocyte-associated antigens, CD11b, CD14, and CD68, also evidenced the remarkable differentiation of U937 cells into monocytes/macrophages by presenting high CD maker positive percentages (>50%). Tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta in CM of HM1-stimulated MNC for 1 day (MNC-CM-1) were 1350 and 1374 pg/mL, respectively, revealing the potent antitumor and differentiation-inducing activities of HM. Of note, MNC-CM-1 appeared to be more effective than day 5 MNC-CM (MNC-CM-5) in both antitumor and differentiation-inducing activities.