Basidiomycetes present different kinds of glucans and heteropolysaccharides. The common monosaccharide composition of these polymers is glucose, galactose, mannose, xylose, and fucose. Normally (1→3),(1→6)-β-glucans are extracted from these organisms, and also galactomannans, heteroglycans, and fucogalactans [2, 4]. Mushrooms included in the same genera show more similarities in their composition, including the structure of carbohydrates . In the present study, we compared two species from the genus Agaricus, which showed comparable NMR profiles. Both extracts contained mixtures of three main polysaccharides and their composition was comparable to what had been observed for other basidiomycete mushrooms, i.e. presenting glucose, galactose, mannose and fucose . A. brasiliensis showed higher contents of β-glucan while A. bisporus presented mannogalactan as main polysaccharide. The proportion of each polysaccharide observed for both species varied significantly, and this may be an explanation for the differences encountered in the biological effects described by other authors. A. brasiliensis is known to be a medicinal mushroom and it has been widely used in Japan for many years for the treatment of cancer and other diseases . A. bisporus, on the other hand, is mainly consumed as food; however there is quite some evidence concerning possible therapeutic properties as reduction of blood glucose  and cholesterol levels , generation of ROS species by human cells , and NO production stimulation .
In this study we evaluated the capacity of the mushroom extracts to stimulate the production of the pro-inflammatory cytokines TNF-α, IL-1β, and the enzyme COX-2 on THP-1 cells. In this assay, the samples were added to the cells and after different incubation periods they were harvested for analysis. The differences between both species were not significant. However a slight increase of expression was observed for the three transcripts induced by the α-amylase treated polysaccharide (ABSE) of A. bisporus. This treatment increased the content of β-glucan and mannogalactan, since it degrades only α-(1→4)-linkages. Although this glycogen-like molecule showed antitumor properties , there are no reports showing an immunostimulatory activity. Galactomannan from M. esculenta  and a polysaccharide from G. lucidum, containing glucose (58.1%), mannose (15.1%), and galactose (13.5%) had been found to stimulate THP-1 and showed an increase in NF-κB expression or were able to activate the differentiation to DC's, respectively . Therefore, the presence of β-glucan may not be the only agent for the effects observed in the present study.
Macrophages contain specific membrane receptors that might bind polysaccharides and/or glycoproteins as Toll-like receptor 4 (TLR4), CD14, complement receptor 3 (CR3), scavenger receptor, dectin-1, and mannose receptor . The binding to these receptors activates the transcription factor NF-κB, which controls the expression of multiple genes in activated monocytes and macrophages. Some of the genes regulated by NF-κB are the pro-inflammatory cytokines, chemokines, and inflammatory enzymes [13, 39]. This could explain the induction of TNF-α, IL-1β, and COX-2 by THP-1 cells after the treatment with the extracts. It is known that the structure of the polysaccharides, as well as their conformation, molecular weight, and solubility in water may influence the receptor ligand interaction . Moradali et al. (2007)  mentioned that triple-helix conformation of glucans and the presence of hydrophilic groups on the outside surface of the helix are important for their biological effect. Considering that the receptors are not specific for glucose polymers, it may be possible that the mannogalactan present in the extracts also bind the receptors, activating the nuclear transcription factor. Besides, the presence of the mannogalactan can also provide a well-suited conformation for the β-glucans, and facilitate their binding to dectin-1, the well-known receptor for glucans . Further experiments should be performed to elucidate the mechanism of the immunomodulatory effects of these polymers.
A complementary study was performed to evaluate the capacity of ABL extract to reduce the expression of pro-inflammatory cytokines. The treatment reduced the expression of IL-1β, and markedly reduced TNF-α production. The addition of ABL concomitantly with LPS or after 3 h was found to reduce or avoid the expression of TNF-α and IL-1β, while the reduction, by adding ABL before LPS, was not effective. It was shown before that CD14 and Toll-like receptor 4 (TLR4) present in macrophages are essential for LPS recognition and consequently for responsiveness to this bacterial endotoxin . Considering that these receptors are probably bound by polysaccharides, it is possible that there is competition between LPS and glucans/mannogalactans when added concomitantly. These experiments led to the conclusion that the semi-purified polysaccharide extracts of A. bisporus and A. brasiliensis can stimulate the production of pro-inflammatory cytokines and enzymes in THP-1 cells, as well as reduce the response to LPS.
It is well known that TNF-α and IL-1β are pro-inflammatory cytokines; therefore they can induce inflammation, fever and tissue damage. Blocking these chemokines could help relieve symptoms of inflammatory processes as in rheumatoid arthritis inflammatory bowel disease and other autoimmune diseases. Contrarily, as TNF-α and IL-1β play an important role against invasive pathogens, their induction may be relevant to increase e.g. antimicrobial resistance . Eventual optimal application will depend on specifications of specific target groups.
The presence of α-glucan in the A. bisporus extract reduced its activity, showing that the β-glucan and the mannogalactan are the major bioactive agents. In addition A. brasiliensis polysaccharide extract reduced the LPS induced synthesis of TNF-α and IL-1β. Both extracts (ABS and ABL) presented comparable effects even though they showed significant differences in the proportion of β-glucan and mannogalactan in their composition. While A. bisporus presents 55.8% of mannogalactan and only 23.7% of β-glucan, A. brasiliensis is composed of 25.2% of mannogalactan and 49.1% of β-glucan.