Compiled by Initiative Team Member Mary Jo Feeney, MS, RD, FADA
The immune system is comprised of a network of cells, tissues, and organs that work together to defend the body against attacks by “foreign” invaders. These are primarily microbes—tiny organisms such as bacteria, parasites, and fungi that can cause infections. Viruses also cause infections. The human body provides an ideal environment for many microbes. It is the immune system’s job to keep them out or, failing that, to seek out and destroy them.
The immune system is amazingly complex. It can recognize and remember millions of different enemies, and it can produce secretions (release of fluids) and cells to match up with and wipe out nearly all of them. When the immune system hits the wrong target, however, several disorders, including allergic diseases, arthritis, and a form of diabetes may result. If the immune system is crippled, other kinds of diseases result.
The immune system relies on an elaborate and dynamic communications network. Millions and millions of cells, organized into sets and subsets, gather like clouds of bees swarming around a hive and pass information back and forth in response to an infection. Once immune cells receive the alarm, they become activated and begin to produce powerful chemicals. These substances allow the cells to regulate their own growth and behavior, enlist other immune cells, and direct the new recruits to trouble spots.
Further information can be found at the U.S. National Institutes of Health, National Institute of Allergy and Infectious diseases: http://www.niaid.nih.gov/topics/immunesystem/pages/whatisimmunesystem.aspx. . Additional information can be found at http://www.niaid.nih.gov/topics/immunesystem/pages/response.aspx. Various health topics are discussed by the World Health Organization at: http://www.who.int/topics/influenza/en/.
See also the sections in Mushrooms & Health that discuss the anti-microbial and antiviral properties of mushrooms.
From the Executive Summary
Immune Function. Numerous studies have described the effects of mushrooms and mushroom extracts on immune function with implications for inhibitory effects on tumour growth. Some of the more efficacious compounds have been reported to be 1,6-branched 1,3-β-glucans which have been reported to inhibit tumour growth by stimulating of the immune system via effects on natural killer (NK) cells, macrophages and via T cells and their cytokine production. More recent work has implicated polysaccharides with varying sugars and some are α- rather than β-glucans. Furthermore, mushroom proteins, terpenes and furans have also been implicated in immune function. While considerable in vitro data have been generated, in vivo studies are few and the small number of clinical studies that have been carried out have often been poorly controlled and with small numbers of patients.
Studies in humans
A double-blind randomized trial has been undertaken in 56 mildly hypercholesterolemic subjects who consumed a control fruit juice with no added alpha-glucans (200 ml/day) for a 2-week run-in period. For the next 5 weeks, the control group (n=30) continued consumption of the control fruit juice, whereas the intervention group (n=26) consumed the same fruit juice enriched with alpha-glucans from Agaricus bisporus (5 g glucans/day). Consumption of A. bisporus alpha-glucans lowered lipopolysaccharideinduced TNFalpha production by 69% compared to the control group, whereas no effect on IL-1beta and IL-6 was observed. A trend towards a decreased production of IL-12 and IL-10 was also observed. The authors suggested that in vivo, alpha-glucans had lost their efficacy to stimulate the immune response as observed in an in vitro mouse model (Volman et al., 2010).
The synergistic effects of Cordyceps sinensis with the drug cyclosporine A in preventing allograft rejection was recently reported in rats (Ding et al., 2009a) but a retrospectively study by the same group has also evaluated the immunoregulatory effect of a dry powder preparation of Cordyceps sinensis mycelia on humans after renal transplantation (Ding et al., 2009b). While there was no significant difference in graft survival rate or occurrence of reject reaction, treatment did effectively protect liver and kidney, stimulate hemopoietic function, improve hypoproteinemia, as well as reduce the incidence of infection and the dosage of the drugs cyclosporine A and tacrolimus used, and therefore, it may be useful for immunoregulation after organ transplantation.
The effect of Agaricus blazei Murill (AbM) on the release of several cytokines in human whole blood both after stimulation ex vivo and in vivo after oral intake over several days has been studied in healthy volunteers (Johnson et al., 2009). After stimulation of whole blood ex vivo with 0.5-5.0% of a mushroom extract, mainly containing AbM, there was a dose-dependent increase in all the cytokines studied, ranging from two to 399-fold (TNFalpha). However, in vivo in the eight volunteers who completed the daily intake (60 ml) of this AbM extract for 12 days, a significant reduction was observed in levels of IL-1beta (97%), TNF-alpha (84%), IL-17 (50%) and IL-2 (46%). Another nine cytokines were measured but they were unaltered. The discrepant results on cytokine release ex vivo and in vivo may partly be explained by the antioxidant activity of AbM in vivo and limited absorption of its large beta-glucans across the intestinal mucosa to the reticuloendothelial system and blood.
In vitro studies (human cell lines)
Numerous studies have described the effects of mushrooms and mushroom extracts on immune function with implications for inhibitory effects on tumour growth. Some of the more efficacious compounds have been reported to be 1,6-branched 1,3-β-glucans which have been reported to inhibit tumour growth by stimulating of the immune system via effects on NK cells, macrophages and via T cells and their cytokine production. More recent work has implicated polysaccharides with varying sugars and some are α- rather than β-glucans. Furthermore, mushroom proteins, terpenes and furans have also been implicated in immune function. While considerable in vitro data have been generated, in vivo studies are few and thesmall number of clinical studies that have been carried out have often been poorly controlled and with small numbers of patients. The immunobiology of mushrooms has recently been reviewed (Borchers et al., 2008), as have the health effects of beta-glucans in mushrooms (Rop et al., 2009, Rondanelli et al., 2009).
Beta glucan from Grifola frondosa (Maitake) has recently been shown to enhance umbilical cord blood stem cell transplantation (from full-term infants) in the nonobese diabetic/severe combined immunodeficient (NOD/SCID) mouse. The Maitake beta glucan (MBG) enhanced mouse bone marrow (BMC) and human umbilical cord blood (CB) cell granulocyte-monocyte colony forming unit (GM-CFU) activity in vitro and protected GM-CFU forming stem cells from doxorubicin (DOX) toxicity. MBG promoted a greater expansion of CD34+CD33+CD38- human committed hematopoietic progenitor (HPC) cells compared to the conventional stem cell culture medium. Oral administration of MBG to recipient NOS/SCID mice led to enhanced homing at 3 days and engraftment at 6 days in mouse bone marrow compared to control mice. More CD34+ human cord blood cells were also retrieved from mouse spleen in beta glucan treated mice at 6 days after transplantation. The studies suggest that Maitake beta glucan promoted hematopoiesis through effects on CD34+ progenitor cell expansion ex vivo and when given to the transplant recipient could enhance CD34+ precursor cell homing and support engraftment (Lin et al., 2009a).
In whole blood, Ganoderma lucidum mycelia have been reported to stimulate tumour necrosis factor-alpha (TNF-alpha) and IL (interleukin)-6 production after 8h of treatment. Interferon-gamma release from human whole blood was also enhanced after 3 days of culture with Ganoderma lucidum mycelia. However, Ganoderma lucidum mycelia did not potentiate nitric oxide production in RAW264.7 cells (Kuo et al., 2006). The protein extracts of V. volvacea and G. lucidum have been shown to contain immunomodulating activity by acting directly on human peripheral blood mononuclear cells and thereby modulating T cell activation (Jeurink et al., 2008). A protein from Ganoderma lucidum has also been shown to effectively promote the activation and maturation of immature human monocyte-derived dendritic cells, preferring a Th1 response, suggesting that the protein may possess a potential effect in regulating immune responses (Lin et al., 2009b). These immunomodulatory effects were shown to be mediated via NF-kappaB and Mitogen Activated Protein Kinase (MAPK) pathways.
A beta-glucan extracted from the fruiting body of the Maitake mushroom (Grifola frondosa) has been reported to activate cellular immunity and expresses anti-tumour effects, with the anti-tumour effects relating to its control of the balance between T lymphocyte subsets Th-1 and Th-2. The fraction decreased the activation of B cells and potentiated the activation of helper T cells, resulting in enhanced cellular immunity. It also induced the production of interferon (IFN)-gamma, interleukin (IL)-12 p70, and IL18 by whole spleen cells and lymph node cells, but suppressed that of IL-4. These results suggest that this fraction establishes Th-1 dominance which induces cellular immunity in the population that was Th-2 dominant due to carcinoma (Inoue et al., 2002). A polysaccharide purified from Ganoderma lucidum has also been shown to induce gene expression changes in human dendritic cells and promote T helper 1 immune response in BALB/c mice (Lin et al., 2006).
Agaricus blazei Murill has been reported to possess biological effects that include immunomodulatory activities, such as stimulation of serum immunoglobulin G level, delayed-type hypersensitivity, splenocyte proliferation rate, and tumour necrosis factor-alpha secretion by splenocytes (Chan et al., 2007). Agaricus blazei has also been reported to have inhibitory effects on mast cell-mediated anaphylaxis-like reactions (Choi et al., 2006b) and up-regulate genes such as the interleukins IL1B and IL8 (Ellertsen et al., 2006). An extract of Agaricus blazei Murill has also been reported to differentially stimulate production of pro-inflammatory cytokines in human monocytes and human vein endothelial cells in vitro (Bernardshaw et al., 2005a). The effects of Agaricus blazei Murill on immunity, infection and cancer have been reviewed (Hetland et al., 2008).
Ethyl acetate extracts of Ganoderma applanata, Naematoloma sublateritium, Pleurotus eryngii, and P. salmoneostramineus have been shown to have in vitro anti-inflammatory activity via cyclooxygenase-2 inhibitory effects compared to COX-1 inhibition, while ethyl acetate extracts of Agrocybe cylindracea exhibited high inhibition of the COX-2 enzyme (Elgorashi et al., 2008). Ceramide from Agrocybe aegerita has also been reported to inhibit the cyclooxygenase enzymes, COX-1 and -2 (Diyabalanage et al., 2008). In RAW 264.7 macrophage cells, Phellinus linteus butanol fractions (PLBF) inhibit the production of NO and PGE2 through the down-regulation of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) gene expression via reactive oxygen species (ROS)-based NF-kappa B and mitogen-activated protein kinase (MAPK) activation suggesting a potential effect on inflammation-associated disorders (Kim et al. 2007)(Kim et al., 2007).
The immunomodulatory effects of mushrooms appear to be unaffected by food processing procedures. Boiling (100°C, 30 min) and freezing (-80°C, 24 h) treatments did not reduce the effects of Agaricus bisporus lectin (ABL) and the immunomodulatory protein of Auricularia polytricha on macrophage-activating functionalities, determined by the induction of TNF-α and NO production by RAW264.7 cells in vitro, while treatment with pH 2 and pH 13 buffers only resulted in an insignificant decrease of the induced TNF-α and NO production. Furthermore, Agaricus bisporus lectin (ABL) and Auricularia polytricha also withstood vacuum dehydration, with 96.5% and 84.6% of activities being retained, respectively, in their stimulations of TNF-α production. These data show thermal/freezing-resistance, acid/alkali tolerance and dehydration stable properties of the extracts tested with respect to their effects as immune stimulants (Chang et al., 2007).
Possible immuno-modulating effects of Ganoderma lucidum mycelium extract (GL-M) and spore extracts on human immune cells have been studied. Dendritic cells (DCs) are antigen-presenting cells and their role in DC-based tumour vaccines has been well defined. The differential effect of GL-M and GL spore extract (GL-S) on proliferation and Th1/Th2 cytokine mRNA expression of human peripheral blood mononuclear cells (PBMCs) and monocytes has been evaluated. The effects on the phenotypic and functional maturation of human monocyte-derived DCs were also investigated. GL-M induced the proliferation of PBMCs and monocytes, whereas GL-S showed a mild suppressive effect. Both extracts stimulated Th1 and Th2 cytokine mRNA expression, but GL-M was a relatively stronger Th1 stimulator. In contrast to GL-S, GL-M enhanced maturation of DCs in terms of upregulation of CD40, CD80, and CD86, and also reduced fluorescein isothiocyanate-dextran endocytosis. Interestingly, GL-M-treated DCs only modestly enhanced lymphocyte proliferation in allogenic mixed lymphocyte culture with mild enhancement in Th development. The data provide evidence that GL-M has immuno-modulating effects on human immune cells and may be of use as a natural adjuvant for cancer immunotherapy with dendritic cells (Chan et al., 2005). Ganoderma lucidum has also been shown to enhance the expression of CD40 and CD80 molecules on human peripheral blood monocytic cells derived from both sexes in a dose-dependent manner (Ahmadi and Riazipour, 2009).
An immunomodulatory protein (FIP-fve) has been isolated and purified from Flammulina velutipes. The complete amino acid sequence of FIP-fve was determined by protein sequencing techniques. FIP-fve consisted of 114 amino acid residues with an acetylated amino end, and lacked methionine, half-cystine and histidine residues. FIP-fve was able to hemagglutinate human red blood cells. The immunomodulatory activity of FIP-fve was demonstrated by its stimulatory activity toward human peripheral blood lymphocytes, and its suppression of systemic anaphylaxis reactions and local swelling of mouse footpads. FIP-fve was found to enhance the transcriptional expression of interleukin-2 and interferon-gamma (Ko et al., 1995).
Phenolic compounds present in mushroom extracts from A. bisporus, A. brasiliensis, and G. lucidum strongly generated reactive oxygen species (suggesting immunomodulatory effects) in human PBMCs and K 562 cells in vitro (Wei et al., 2008).
Vitamin D is an important factor for immune function. Mushrooms are a good source of vitamin D and studies have reported that sunlight-activated biosynthesis of vitamin D from ergosterols within mushrooms (fresh and dried) can increase vitamin D levels considerably, which has significant implications in the context of health (Stamets, 2005). Vitamin D2 levels can also be significantly increased by irradiation of mushrooms with ultraviolet light (Jasinghe and Perera, 2006) with the effects being proportional to surface area, e.g. a more efficient way of increasing the vitamin D2 content is to irradiate sliced mushrooms (Ko et al., 2008). Ganoderma lucidum can biotransform 20%-30% of inorganic Se from substrate with Se being biotransformed preferentially in forms of Se-containing proteins. The immune-regulatory activities of both Se and proteins from G. lucidum appear to be synergistic (Du et al., 2008).
Animal model (mouse) studies
Alpha-glucan-beta-glucan-protein complex polysaccharide from Agaricus blazei administered intraperitoneally or orally to Sarcoma 180 transplanted mice had no direct cytotoxic action on tumour cells in vitro. However, the polysaccharide showed a strong in vivo tumour growth-inhibitory effect suggesting that the effect of the polysaccharide is due to host-mediated mechanisms (Gonzaga et al., 2009). There is growing evidence that such effects of a variety of mushrooms are mediated via promotion of natural immunity though macrophages, dendritic cells and NK cells. These cells attack cells infected with pathogens such as bacteria and viruses and produce cytokines, such as interferon-gamma (IFN-γ), which can modulate natural and specific immune responses. Gandoderma lucidum extracts have also been shown to promote immune responses in normal BALB/c mice (Chang et al., 2009a) and WEHI-3 leukemic BALB/c mice (Chang et al., 2009b).
It has been demonstrated that dietary supplementation with white button mushrooms (Agaricus bisporus) enhances natural killer (NK) cell activity in C57BL/6 mice, suggesting that increased intake of white button mushrooms may promote innate immunity against tumours and viruses through the enhancement of NK activity (Wu et al., 2007a). Agaricus bisporus has been shown to enhance maturation of bone marrow-derived dendritic cells of C57BL mice. A functional assay for dendritic cell maturation showed that mushroom supplementation decreased cell endocytosis and increased intracellular interleukin (IL)-12 levels suggesting an enhancement of both innate and T cell-mediated immunity leading to a more efficient surveillance and defence mechanism against microbial invasion and tumour development (Ren et al., 2008b).
A polysaccharide extracted from the Maitake mushroom (Grifola frondosa S.F. Gray) has been shown to stimulate natural immunity in normal C3H/Hej mice. This effect was related to the activation of NK cells indirectly through IL-12 produced by macrophages and dendritic cells (Kodama et al., 2003). A subsequent study from this group has suggested that the mechanism by which NK cells are activated is mediated through cytokines produced by antigen-presenting cells (Kodama et al., 2010). In Sarcoma-180bearing mice, proteoglycans from Pleurotus ostreatus mycelia, have been shown to elevate mouse natural killer (NK) cell cytotoxicity and stimulated macrophages to produce nitric oxide (Sarangi et al., 2006).
Polysaccharides from Flammulina velutipes have also been shown to promote the metabolic activity of murine splenocytes and peritoneal exudate cells (PEC) and increase the amounts of TNF-alpha, INF-gamma and IL-2 in the supernatants of splenocyte cultures, and the amount of TNF-alpha in PEC cultures, with the most marked increase on TNF-alpha level. Flammulina velutipes polysaccharides (100, 50, 25 mg/kg) raised the serum levels of TNF-alpha and INF-gamma in Sarcoma-180 tumour-bearing mice. Flammulina velutipes polysaccharides may regulate murine immune function through promoting the production of TNF-alpha, INF-gamma and IL-2 (Chang et al., 2009a). A beta-glucan from Agrocybe chaxingu significantly inhibited lipopolysaccaride (LPS)induced nitric oxide (NO) and cyclooxygenase-2 (COX-2) expression levels in murine macrophage Raw 264.7 cells. Furthermore, topical application of the polysaccharide resulted in marked inhibition of 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced ear edema in mice. These results suggest that this polysaccharide may be useful for the treatment of NO- and COX-2-related disorders such as inflammation (Lee et al., 2009a). Ganoderma lucidum (Leyss: Fr) Karst. has also been shown to trigger immunomodulatory effects and reduce nitric oxide synthesis in Swiss male mice (Rubel et al., 2010)
Oral administration of a protein from Flammulina velutipes has also been shown to possess anti-tumour activity in mice through activation of both innate and adaptive immunity of the host to prime a cytotoxic immune response with interferon-gamma having an effect on the anti-tumour efficacy of the protein (Chang et al., 2010).
A recent study has also suggested that oral administration of a submerged cultivated G. frondosa mixture to normal mice may enhance host innate immunity against foreign pathogens without eliciting an adverse inflammatory response (Wang et al., 2008).
Polysaccharides from Flammulina velutipes have also been shown to promote the metabolic activity of murine splenocytes and peritoneal exudate cells (PEC) and increase the amounts of TNF-alpha, INF-gamma and IL-2 in the supernatants of splenocyte cultures, and the amount of TNF-alpha in PEC cultures, with the most marked increase on TNF-alpha level. Flammulina velutipes polysaccharides (100, 50, 25 mg/kg) raised the serum levels of TNF-alpha and INF-gamma in Sarcoma-180 tumour-bearing mice. Flammulina velutipes polysaccharides may regulate murine immune function through promoting the production of TNF-alpha, INF-gamma and IL-2 (Chang et al., 2009a)
2-Amino-3H-phenoxazin-3-one (APO) from an extract of Agaricus bisporus IMBACH has been shown to inhibit NO production by mouse peritoneal macrophages in response to the pro-inflammatory stimuli lipopolysaccharide (LPS) and interferon (IFN)-gamma (LPS/IFN-gamma) at low concentrations (IC50=1.5 µM) through reduced inducible NO synthase protein expression. APO inhibited both cyclooxygenase (COX)-1 and COX-2 enzyme activities with almost equal selectivity (Kohno et al., 2008).
Mushroom (Shiitake) extracts have been dispersed with lecithin micelles to prepare superfine particles (0.05 to 0.2 microns in diameter) of beta-1,3-glucan (micellary mushroom extracts). When mice were fed with these micelles of beta-glucan (0.75mg/day/mouse, smaller amounts of beta-glucan), the number of lymphocytes yielded by the small intestine increased by up to 40% and tumour cytotoxicity against P815 cells and cytokine production was also augmented, suggesting that smaller amounts of micellary beta-glucan might be useful for the potentiation of intestinal immunity (Shen et al., 2007). The Shiitake mushroom-derived immuno-stimulant lentinan has also been reported to protect against murine malaria blood-stage infection by evoking adaptive immune-responses (Zhou et al., 2009).
Phellinus linteus contains constituents that exhibit potent anti-tumour effects through activation of immune cells. A recent study in mice has reported that boiling water soluble fractions from mycelium of P.linteus contain anti-allergic and immuno-potentiating properties (Inagaki et al., 2005). Cordyceps sinensis has also been shown to possess immuno-potentiating effects in lupus-prone autoimmune (NZB/NZW) mice via action on peripheral mononuclear T lymphocytes. These effects also reportedly attenuated the severity of lupus in these mice (Chen et al., 2009a). A polysaccharide isolated from cultured Cordyceps sinensis (named cordysinocan), has been reported to activate immune responses in cultured T-lymphocytes and macrophages, partly via the induction of cytokines (Cheung et al., 2009). Orally administered glucans from Pleurotus pulmonarius have also been recently reported to reduce acute inflammation in dextran sulfate sodium-induced experimental colitis in mice (Lavi et al., 2010).
Animal model (rat) studies
The effects of pleuran, a beta-glucan isolated from Pleurotus ostreatus, have been studied in a model of acute colitis in rats. Pleuran was given either as a 2% food component or as 0.44% pleuran hydrogel drink over 4 weeks. Colitis was induced by intraluminal instillation of 4% acetic acid and after 48h the extent of colonic damage and several biochemical parameters were examined. Pleuran supplementation both in food and in drinking fluid significantly decreased the disposition to colitis. The enhanced activity of myeloperoxidase in the inflamed colonic segment was reduced by pleuran diets, reflecting decreased neutrophil infiltration. The mechanism of the described protective effect of pleuran is not yet clear, but the authors suggest that the pleuran-enhanced antioxidant defence of the colonic wall against the inflammatory attack maybe a factor (Bobek et al., 2001).
A protein-bound polysaccharide extracted from Coriolus versicolor has been shown to have an immuno-potentiating effect, being effective in restoring cyclophosphamide (CPA)-induced immuno-suppression such as depressed lymphocyte proliferation, natural killer cell function, production of white blood cells and the growth of spleen and thymus in rats as well as in increasing both IgG and IL-2 production on which CPA did not have significant effects. The protein-bound polysaccharide partly restored CPA-induced immuno-suppression. The authors suggested that the protein-bound polysaccharide could be considered as a useful adjuvant, particularly combined with CPA or other chemotherapy in clinical treatment of cancer patients. The mechanism by which the protein-bound polysaccharide restored the immuno-suppression induced by CPA is unclear (Qian et al., 1997).
Summary of Immune Function
Numerous studies have described the effects of mushrooms and mushroom extracts on immune function with implications for inhibitory effects on tumour growth. Some of the more efficacious compounds have been reported to be 1,6-branched 1,3-β-glucans which have been reported to inhibit tumour growth by stimulating of the immune system via effects on natural killer (NK) cells, macrophages and via T cells and their cytokine production. More recent work has implicated polysaccharides with varying sugars and some are α- rather than β-glucans. Furthermore, mushroom proteins, terpenes and furans have also been implicated in immune function. While considerable in vitro data have been generated, in vivo studies are few and the small number of clinical studies that have been carried out have often been poorly controlled and with small numbers of patients.
Mushroom lectins have been reported to be immuno-modulatory proteins. They have been demonstrated to have thermal/freezing resistance, acid/alkali tolerance and dehydration stable properties suggesting that they would be stable during food processing applications and therefore suitable for functional food/health utilization.
Some mushrooms (e.g. Shiitake, Lentinus edodes) possess anti-microbial properties, demonstrated in vitro, which appear to involve the native immune system, via enhancement of the level of cytokines.