INTERNATIONAL JOURNAL OF IMMUNOTHERAPY XIV(i)
Summary: Arabinoxylane, from rice bran (MGN-3) was examined for its augmentory effect on human natural killer 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-natural killer cell activity was tested by 51CR-release assay against K562 and Raji tumor cells at 1 week, 1 month and 2 months post-treatment and results were compared with baseline natural killer activity. Treatment with MGN-3 enhanced natural killer activity against K562 tumor cells at all concentrations used. In a dose-dependent manner, MGN-3 at 15 mg/kg/day increased natural killer activity after 1 month post-treatment (two-fold over control value), while significant induction of natural killer activity at 30 mg/kg/day was detected as early as 1 week post-treatment (2 1/2 times control value). Natural killer cell activity continued to increase with continuation of treatment and peaked (five-fold) at 2 months (end of treatment period). Increasing the concentration to 45 mg/kg/day showed similar trends in natural killer activity. However the magnitude in values was higher than for 30 mg/kg/day. After discontinuation of treatment, natural killer activity declined and returned to baseline value (14 lytic units) at 1 month. Enhanced natural killer activity was associated with an increase in the cytotoxic reactivity against the resistant Raji cell line. MGN-3 at 45 mg/kg/day showed a significant increase in natural killer activity after 1 week (eight-fold) and peaked at 2 months post-treatment (27 times that of baseline). Culture of peripheral blood lymphocytes with MGN-3 for 16 hours demonstrated to a 1.3 to 1.5 times increase in natural killer activity over the control value. The mechanism by which MGN-3 increases natural killer activity was examined and showed no change in cluster of differentiation (CD) 16+ and CD56+ CD3+ of MGN-3 activated natural killer cells as compared with baseline value; a four-fold increase in the binding capacity of natural killer to tumor cell targets as compared with baseline value; and a significant increase in the production of lnterferon-y (340-580 pg/mL). Postculture of peripheral blood lymphocytes with MGN-3 at concentrations of 25-100 pg/mL. Thus, MGN-3 seems to act as a potent immunomodulator causing augmentation of natural killer cell activity, and with the absence of notable side-effects, MGN-3 could be used as a new biological response modifier having possible therapeutic effects against cancer.