## 4 Discussion  
Mushrooms are a food resource which are distributed across the globe and consumed for their nutritional value [26; 27]. In addition, mushrooms contain a variety of nutrients, such as carbohydrates, protein, minerals and terpenoids, which are beneficial for human health [28; 29; 30]. Many bioactive compounds of medicinal mushrooms have been extensively studied including polysaccharides, lectins, lactones, terpenoids and alkaloids [31]. Among them, polysaccharides with multiple activities are the main components of some mushrooms [26]. In recent years, more and more attention has been paid to the immunomodulatory function of mushroom polysaccharides. The phagocytosis of macrophages is one of the main mechanisms of body defense against foreign body invasion [32]. NO is one of the main effector molecules produced by macrophages. NO not only enhances the activity of macrophages, but also plays an important regulatory role in innate immunity and adaptive immunity as an important signaling molecule [33]. In this study, we firstly explored whether GPP regulated macrophage function in vitro. The results showed that GPP has the tendency to increase the ability of phagocytic neutral red and release of NO compared with the GLP group (Figure 1). Moreover, GPP significantly enhanced the ability of phagocytosis at the concentrations of 100 and 200 mg/mL (\(p<0.01\), \(p<0.05\)), and significantly enhanced the ability of macrophages to release NO at the concentrations of 50 and 100 mg/mL (\(p<0.05\)), when compared with the PUP group (Figure 1). Figure 5: GPP increased peripheral phagocytes and NK cell activity in mice. The uptaking capacity of peripheral phagocytes was detected by mouse peritoneal macrophage phagocyte chicken erythrocytes test, and the (**a**) phagocytic rate and (**b**) phagocytic index represented the phagocytosis of macrophages. (**c**) An LDH releasing assay was used to detect the NK cell activity of the spleen. Data were expressed as mean \(\pm\) SEM (N = 12). \({}^{**}p<0.01\) vs. control group. The results indicated that GPP enhanced the phagocytic ability and NO production of macrophages compared with GLP or PUP to some extent. According to the above experimental results, the mRNA expression of iNOS, which was closely related to the production of NO, was detected by RT-qPCR. The result (Figure 2a) showed that the expression mRNA of iNOS was significantly increased in each experimental group compared with the control group at the concentration of 100 \(\mathrm{\SIUnitSymbolMicro g}\)/mL. Moreover, the mRNA expression of iNOS was the highest in the GPP group, indicating that GPP could significantly enhance the mRNA expression of iNOS. Macrophages have the characteristic of being heterogeneous, and their phenotypes and functions are regulated by the surrounding microenvironment [34; 35]. In response to exogenous stimuli, macrophages polarized into different phenotypes in different stages of inflammatory response [36]. There are mainly two subtypes, namely classical polarization (M1 type) or alternating polarization (M2 type) [36; 37]. The equilibrium polarization of macrophages M1/M2 controls the fate of inflammatory or damaged organs. The function of M1 macrophages are involved in the inflammatory response, pathogen clearance, antitumor immunity [38], and enhancing phagocytosis and releasing TNF-\(\alpha\), IL-6 and other pro-inflammatory factors [21; 38]. In this study, there was no significant change in IL-6 mRNA expression in each experimental group compared with the control group (Figure 2d). However, the mRNA expression of TNF-\(\alpha\) was significantly increased (Figure 2b), and the mRNA expression of TNF-\(\alpha\) in the GPP group was higher than that in the GLP group and PUP group, although without statistical significance, indicating that GPP could enhance the mRNA expression of TNF-\(\alpha\). If M1 macrophages are continuously enhanced, they will lead to tissue damage.