ENHANCEMENT OF HUMAN NATURAL-KILLER-CELL ACTIVITY BY MODIFIED ARABINOXYLANE FROM RICE BRAN (MGN-3)

Arabinoxylane from rice bran (MGN-3) was examined for its augmentory e ffect on human NK (NK) cell activity in vivo and in vitro. Twenty-four individuals were given MGN-3 orally at three different concentrations : 15, 30 and 45 mg/kg/day for 2 months. Peripheral blood lymphocyte-NK cell activity was tested by Cr-51 release assay against K562 and Raji tumor cells at I week, I month and 2 months posttreatment and results were compared with baseline NK activity Treatment with MGN-3 enhanced NK activity against K562 tumor cells at all concentrations used. In a dose-dependent manner, MGN-3 at 15 mg/kg/day increased NK activity af ter 1 month posttreatment (twofold over control value), while signific ant induction of NK activity at 30 mg/kg/day was detected as early as I week posttreatment (three times control value). NK cell activity con tinued to increase with continuation of treatment and peaked (fivefold ) at 2 months (end of treatment period). Increasing the concentration to 45 mg/kg/day showed similar trends in NK activity, however the magn itude in values was higher than for 30 mg/kg/day After discontinuation of treatment, NK activity declined and returned to baseline Value (14 lytic units) at I month. Enhanced NK activity was associated with an increase in the cytotoxic reactivity against the resistant Raji cell l ine. MGN-3 at 45 mg/kg/day showed a significant increase in NK activit y after I week (eightfold) and peaked at 2 months posttreatment (27 ti mes that of baseline). Culture of peripheral blood lymphocytes (PBL) w ith MGN-3 for 16 h demonstrated a 1.3 to 1.5 times increase in NK acti vity over control value. The mechanism by which MGN-3 increases NK act ivity was examined and showed no change in cluster of differentiation (CD)16(+) and CD56(+) CD3(-) of MGN-5-activated NK cells as compared w ith baseline value; a fourfold increase in the binding capacity of NK to tumor cell targets as compared with baseline value; and a significa nt increase in the production of interferon-gamma (340-580 pg/ml) post culture of PBL with MGN-3 at concentrations of 25-100 mu g/ml. Thus, M GN-3 seems to act as a potent immunomodulator causing augmentation of NK cell activity, and with the absence of notable side-effects, MGN-3 could be used as a new biological response modifier (BRM) having possi ble therapeutic effects against cancer.