Effects of Oral Administration of Phellinus linteus on the Productions of the Th1- and Th2-type Cytokines in Mice

Background: The mushroom Phellinus linteus (PL) has been shown to have the anti-tumor and immunostimulatory effects. We hypothesized that the hot water extract of PL (WEPL) exerts its significant immunostimulatory effect by inducing production of the Th1-derived cytokine interferon-${\gamma}$ (IFN-${\gamma}$) by T lymphocytes. Methods: T lymphocytes were isolated from the mice fed with 200 mg/kg of WEPL once a day for 4 weeks, and then stimulated with the mitogen concanavaline A (Con A). IFN-${\gamma}$ gene and intracellular protein expressions were analyzed by RT-PCR and flow cytometry, respectively. The production of IFN-${\gamma}$ was measured by enzyme-linked immunosorbent assay. Results: WEPL significantly enhanced the transcription of IFN-${\gamma}$ mRNA. The effect of WEPL on IFN-${\gamma}$ expression was further supported by a concomitant increase in the number of cells with intracellular IFN-${\gamma}$ protein as well as the secretion of IFN-${\gamma}$. However, WEPL did not modulate either gene expression or protein secretion of interleukin-4, a Th2-associated cytokine, by Con A-stimulated T lymphocytes. Conclusion: Our results demonstrate that one of the potentially beneficial anti-tumor and immunostimulatory effects of WEPL may be mediated through the enhancement of IFN-${\gamma}$ secretion by T lymphocytes.