Induction of Gene Expression of Immunomodulatory Cytokines in the Mouse by a Polysaccharide from Ganoderma lucidum (Curt.: Fr.) P. Karst. (Aphyllophoromycetideae)

Ganoderma lucidum polysaccharide (GLP), isolated by hot aqueous extraction and ethanol precipitation from fruiting bodies of this medicinal mushroom, significantly suppressed in vivo the growth of Sarcoma 180 solid tumor, and thus exhibited antitumor activity. However, GLP showed no direct antiproliferative effect as evaluated in vitro using several cancer cell lines, such as breast cancer MCF-7, lung cancer SPC-A, and hepatoma SMMC-7721. A host-mediated defense mechanism was proposed as the antitumor effect of G. lucidum. To facilitate the study of its antitumor mechanism of action, GLP was divided-into two portions, GLPO (MW < 12,000) and GLPI (MW > 12,000) by dialysis against distilled water, which was injected intraperitoneally into male inbred BALB/c mice. The immunomodulatory action of GLP was elucidated through analyzing the induced expression profile of cytokines in the mice using primers of specific cytokines, total RNA, and reverse transcription-polymerase chain reaction (RT-PCR). The results show that 7 out of 17 cytokine-mRNAs were detected in the splenocytes and peritoneal exudate cells (macrophages) from the control and treated mice. Among the seven detectable cytoldne genes in the splenocytes, GLP induced a marked increase in the expression levels ofinterleukin (IL)-la (2-fold), IL-lb (3-fold), TNF-a (2-fold), IL-12 p35 (up to 6-fold), and IL-12 p40. In the macrophages, GLP promoted a remarkable increase in the expression levels ofIL-lb (2.5- to 3-fold), TNF-a (up to 6-fold), and macrophage colony-stimulating factor (M-CSF) (up to 2-fold). These results indicated that antitumor GLP was able to induce a cascade of immunomodulatory cytokines, but the potentiadon of their gene expression and interaction seemed quite complicated. The potency of TNF-a induction in macrophage is much more up-regulated after the challenge of GLPO than GLPI, and therefore, it is concluded that molecular size might be one of the factors in determining the structure-function relationship of this polysaccharide.