RESUMO
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.