## 4 Discussion
At this point, M2 macrophages would secrete large amounts of IL-10, arginase-1 (Arg1) and other anti-inflammatory factors to inhibit inflammation, promote tissue repair and reconstruction, angiogenesis, and maintain homeostasis [38]. We found that the mRNA expression of the anti-inflammatory factor IL-10 in each experimental group was significantly enhanced compared with the control group (Figure 2c). The experimental results showed that GPP could regulate the immune function of macrophages from multiple perspectives, but overall enhanced the function of M1 macrophages. In the animal experiment, the result of the acute oral toxicity test of GPP showed that the LD50 of GPP in mice was greater than 16.0 g/kg body weight (Figure 3a). According to the classification standard of acute toxicity of health food, the oral acute toxicity of GPP belonged to the non-toxic grade. To investigate the effect of GPP on the regulation of immune function, the ICR mice were given GPP (36, 120, 360 mg/kg) at different concentrations by gavage for 30 days, and there was no significant difference in weight gain among the groups (Figure 3b). The spleen index and thymus index could reflect the level of immune function of the body to some extent [39]. The effect of drugs on the thymus index and spleen index can be used as a preliminary indicator to study the mechanism of animal immunopharmacology [25]. In this paper, both the spleen index and thymus index were not significantly changed compared with the control group, suggesting that the GPP did not affect the size of the spleen and thymus (Figure 4b). The mononuclear macrophage system and NK cells belong to innate immunity. The mononuclear macrophage system is an important part of innate immunity, and is composed of mononuclear cells, macrophages and their precursor cells in bone marrow [40]. Mononuclear cells exist in blood. When mononuclear cells enter tissues through blood vessels, they become macrophages. The NK cell is an important innate immune cell, which has a strong cytolytic function to tumor cells, virus infected cells and other physiological stress cells [41]. NK cell activity is an important indicator of the nonspecific immune system [42]. To investigate their effect on the mouse innate immune function, we tested the phagocytic function of mononuclear macrophages and the activity of NK cells. In the experiment of the peritoneal macrophage phagocytosis of chicken erythrocytes, GPP significantly enhanced the function of mouse peritoneal macrophage phagocytosis of chicken erythrocytes at doses of 120 and 360 mg/kg, suggesting that GPP enhanced the phagocytosis of mouse peritoneal macrophage (Figure 5a,b). In the NK cell viability test, the NK cell activity of mice in the medium-dose (120 mg/kg) group was significantly enhanced compared with that in the control group, suggesting that GPP significantly enhanced the NK cell activity of mice (Figure 5c). The above results showed that GPP could enhance the innate immune function of mice. Our results also showed that GPP could affect the function of macrophages directly or indirectly, which indicated that GPP could affect some signal pathways of macrophages directly or affect the function of macrophages in another way. However, the mechanism of GPP is not yet clear, and needs to be further explored. Some studies have been reported that mushroom polysaccharides could affect immune function by interaction with gut microbiota [4; 43; 44]; therefore, we will explore the mechanism of GPP by studying the relation between GPP, gut microbiota, and the innate immune system.