Immune Modulation Effect of Administration of Rice Bran Extract with Increased Solubility Fermented by Lentinus edodes UBC-V88 in Cyclophosphamide-Treated Mice Model

There is a global and increasing demand for natural ingredients that support the human immune response. In this study, the immunomodulatory effect and mechanism of action of rice bran extract fermented by Lentinus edodes was investigated. The potential immunomodulatory effect of fermented rice bran (FRB) and processed rice bran (RB) was evaluated using male BALB/c mice whose immunity was lowered by Cyclophosphamide (CY). The changes in the weight of the thymus and the spleen, immunoglobulins, and cytokine expressions were measured as biomarkers of immunomodulating potential after 14 days of oral administration of FRB and RB (0.5 g/kg-body weight (b.w.), respectively). The FRB and RB groups treated with CY resulted in increased weight of the thymus (1.73 ± 0.40 and 1.45 ± 0.43 mg/g-b.w., respectively) compared to the CY-treated control group (1.05 ± 0.36 mg/g-b.w.). The levels of the immunoglobulin (Ig) G in the group treated with FRB (21.98 ± 2.17, p < 0.01) were significantly increased when compared to the RB group (18.48 ± 1.52 μg/mL, p < 0.01). The expression of serum cytokines, including IL-1α (p < 0.05), IL-2 (p < 0.05), IL-6 (p < 0.001), IL-12 p70 (p < 0.01), IFN-γ (p < 0.01), and TNF-α (p < 0.01) were also significantly increased by the administration of FRB (0.5 g/kg-b.w.). Similarly, the expression of spleen cytokines, including IL-1α (p < 0.05), IL-2 (p < 0.05), IFN-γ (p < 0.01), and TNF-α (p < 0.05), was also significantly increased in the group receiving the FRB (0.5 g/kg-b.w.). The natural killer cell (NK) cell activities at a 1:25 ratio of YAC-1 cells to splenocytes were significantly increased in positive control red ginseng extract 0.5 g/kg (38.64 ± 2.13%, p < 0.05), FRB (34.85 ± 3.45%, p < 0.05), and RB (25.00 ± 4.18%), compared to that of negative control CY group (12.67 ± 3.23%). These results suggest that FRB administration could stimulate the innate immune system by increasing the expression of cytokines in splenocytes and serum, especially IFN-γ, IL-2, and IL-12 (p70), which are associated with TNF-α and NK cell activities. The above results could provide the biochemical rationale to further evaluate the use of FRB for immunomodulatory applications.