1.1 Mechanism of action of -glucan
The immunomodulatory effects of polysaccharides on the body are mainly realized through the following ways: It plays a role by regulating the expression level of related genes. It works through signal transduction in immune cells.
1.1.1 Function through polysaccharide receptors
A large number of studies have shown that - (1,3) -glucan is binding to monocytes, macrophages, neutrophils and NK cells, indicating the role of glucose receptors [9,10]. Complement 3 (CR3) receptor exists on monocytes, macrophages, neutrophils and NK cells. The receptor contains two functional domains, one of which binds to the cleavage fragment (iC3b) of complement 3 and is called as the (iC3b) binding site. After binding to -glucan, the other domain is preactivated by the above immune cells, which bind effector cells and target cells together through iC3b. Mueller et al.  showed that - (1,3) -glucan specific receptors were present in monocytes and macrophages, suggesting that the binding of glucan ligands to monocytes surface receptors could lead to nf-kb activation, il-6 mRNA expression, and glucose endogenation.
1.1.2 Play a role by regulating the expression levels of related genes
Polysaccharides can also promote cytokine secretion by promoting cytokine gene expression. In the immune response, the expression of iNOS and several other genes is often regulated by NF-KB at the transcriptional level. Studies on the molecular mechanism of yeast polysaccharides promoting TNF synthesis in macrophages have reported that yeast polysaccharides can significantly increase the activity of NF-KB, thereby increasing the activity of TNF gene promoter and the expression of TNF. INOS can induce macrophages to produce a large amount of NO, and NO is a cell signaling molecule with extensive biological activity. It can participate in the regulatory effects of nerve and immunity, affect the proliferation of T lymphocytes, regulate the secretion of cytokines of T lymphocytes and macrophages, and enhance the killing of microorganisms by macrophages.
1.1.3 It plays a role through signal transduction of immune cells
Intracellular calcium ions and cAMP with cGMP are important second messenger molecules. Intracellular Ca2 + active protease C (PKC), synergy with the DAG, jointly promote other activation information transmission effect of protein and protein, function and regulation of cellular immune function, its main division of the lymphocyte proliferation, promote the secretion of IL - 2 T lymphocytes release, mediating the phagocytosis of macrophage, and studies have shown that polysaccharide can cause the change of calcium ion concentration in macrophages . As the second messenger of cAMP, the effect of cAMP is opposite to that of cGMP. During cell proliferation, the concentration of intracellular cAMP increases, while when cell proliferation stops, the concentration of cGMP increases. Studies have shown that glucan can regulate the concentration of cAMP and cGMP in lymphocytes and play a regulatory role in the immune function of the body.
1.2 MOS mechanism
The cell wall of yeast is also an important source of oligosaccharide mannose oligosaccharide (MOS). The two main functions of mannose oligosaccharide are to adsorb intestinal pathogens to regulate non-immune regulatory mechanisms and to regulate cellular and humoral immune regulatory mechanisms.
1.2.1 Effect on the adsorption of intestinal pathogens to regulate non-immune regulatory mechanisms
First of all, for the adsorption of pathogens, the digestive tract provides a large surface area for the invasion of pathogenic microorganisms. The most important step for pathogenic microorganisms to infect the body lies in their colonization of intestinal epithelial cells. Therefore, for pathogenic pathogens such as e. coli and salmonella, successfully attached to the animal intestinal mucosa is a critical step in the whole process of infection, the mechanism is: pathogenic bacteria through its appendages, flagella or fluffy exogenous lectin to host epithelial membrane receptor specificity of sugar "recognition, and with the receptor and attached to the intestinal wall, thrive in the gut, secrete toxins, leading to the occurrence of diseases . Sugars and intestinal tract and the dew in the yeast cell wall is very similar to specific receptors, the combination of pathogenic bacteria and intestinal receptor specificity of sugar can be dew oligosaccharides and their analogues is interrupted, at the same time, such as salmonella and e. coli pathogenic microbes with glucose as the main source of energy, such as bifidobacterium and lactobacillus bacteria in sugar as the main energy source, pathogenic bacteria can not use MOS  and the lack of energy, moreover after pathogen exogenous lectin with dew oligosaccharides can lose with the deactivation and host sugars receptor sites in combination with the dew on the intestinal mucosa ability, so the pathogenic bacteria died and in vitro.
1.2.2 Regulation of cellular and humoral immune regulation
The immune defense system of most animals is used to protect the surface of the gastrointestinal tract from pathogenic bacteria. About 75% of the immune cells and intestinal lymphoid tissue of the body exist in the intestinal tract as part of gut-associated lymphoid tissue (GALT). GALT has non-specific immunity and specific immunity. Non-specific immunity is the first line of defense for invading pathogens, and macrophages play an important role in the process of phagocytosis and killing of invading microorganisms in the early stage of non-specific immune response. Phagocytic antigens are the initial stimulation of macrophages, followed by further activation by TH cell cytins and invading microbial cell wall secretions. The cell wall secretions of exogenous microorganisms can activate the complement of the immune system and regulate the activity of macrophages through the bypass pathway, which accelerates the elimination of pathogenic micro-bacteria.
Studies have shown that the dew oligosaccharides to airframe immunity can be act as immune stimulation of cofactors and play a role, Sharon  research is put forward, such as sugars can not only connect the dew on the bacteria, and can be connected to the toxins, viruses, eukaryotes, after combining the dew oligosaccharide additives can be used as the exogenous antigen, alleviate the absorption of antigen, enhance the cellular immunity and humoral immunity. Mannose oligosaccharides can interact with protein receptors on the surface of intestinal villi immune cells or conduct immune regulation by interfering with the signal system existing in lymph nodes and mucosal propria memory cells .
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