EVALUATION OF THE IMMUNOMODULATORY ACTIVITIES OF THE AQUEOUS EXTRACT AND THE BETA–D-GLUCAN-RICH POLYSACCHARIDE FRACTION OF PLEUROTUSTUBERREGIUM (PLEUROTACEAE)

ABSTRACT

Mushroom cuisines are global delicacies and have been used for decades, not only as food, but mostly for the health benefits which are claimed or scientifically proven. The present study explored the immunomodulatoryactivites of the hot aqueous extract of a local oyster mushroom, Pleurotustuberregium (Fr.) Singer (Pleurotaceae) (PT) and its β–D-Glucan-Rich Polysaccharide fraction (BGP).The effects of the aqueous extract (PT) and the β–D-Glucan-Rich Polysaccharide fraction (BGP) were tested on some specific and non-specific immune responses in immune-competent mice and in culture of RAW 264.7 macrophage cells. The effect of the PT and BGP on specific cell mediated immune response was investigated by the delayed type hypersensitivity response (DTHR) whilethe effect of the extract on specific humoral immune responses of treated mice was determined by prime-boost immunization protocol using ovalbumin as antigen and followed by the determination of antibody titers in the sera using the enzyme-linked immunosorbent assay (ELISA).Their effect on non–specific immune responses was determined by the colloidal carbon-clearance assay in mice. The effect of BGP on functional maturation and activation of the monocytic cells was also determined by measuring the level of tumour necrosis factor (TNF)-α and inducible oxygen (iNO) expressed into culture supernatant using cytokine capture ELISA and Griess reagent respectively.Short-term oral administration of PT (100, 200 and 400mg/kg) or BGP (100 and 200mg/kg) elicited a dose-related increase in DTHR and increased the mean phagocytic clearance of colloidal carbon in mice as much as 7 – 10 fold when compared to the clearance in the untreated group of mice. In a homologous prime-boost immunization schedule, oral supplementation with PT (100, 200 and 400mg/kg) or BGP (100 and 200mg/kg) significantly (P<0.05) increased primary and secondary ovalbumin (OVA) – specific total IgG, IgG1 and IgG2a titres in treated mice as much as 2 – 4 folds compared to the untreated control. In cell culture, stimulation of RAW 264.7 macrophages with BGP (5-1000 µg/ml) induced a remarkable and significant (P<0.05) proliferation of total spleenocytes in a concentration-related manner. Stimulation of RAW 264.7 cells with BGP (5-100 µg/ml) significantly (P<0.05) increased the levels of expressed TNF-α and iNO in culture. Similarly, prestimulation of RAW 264.7 cells significantly (P<0.05) increased the phagocytic capacity of the macrophages in a neutral dye uptake assay. Acute toxicity tests revealed that even at doses of PT up to 5000mg/kg body weight (per os), there was no lethality or any sign of acute intoxication in the mice after 24 h. Put together, the result of these investigations suggest that hot aqueous extract of P tuberegium (PT) and its β–D-Glucan-rich polysaccharide fraction (BGP) possess some immunomodulatory activities in mice and could be further investigated and harnessed for therapeutic purposes in immunodeficiency conditions.