# Research Progress of Polysaccharide-Gold Nanocomplexes in Drug Delivery
## 2 Biological Activity of Polysaccharides  
Polysaccharides, which can be found in abundance in plants, animals, bacteria, and microorganisms, are a prominent type of natural polymers. They possess remarkable immune enhancement properties, promoting improvements in humoral, cellular, and mucosal immune responses. Moreover, these complex molecules have exhibited therapeutic potential in treating diverse diseases, including tumors, infections, and autoimmune disorders [36]. Numerous studies have extensively investigated the various biological activities of polysaccharides, with the primary emphasis placed on immune regulation [37], antitumor [38], antivirus [39], anti-coagulation [40], and antioxidation [32]. The biological activity of polysaccharides is intricately linked to several factors, including monosaccharide composition, glycoside bond type, spatial structure, molecular weight, and branched chain structure [41]. Various factors affecting polysaccharide activity of polysaccharides have been investigated in recent years (Figure 2). Numerous studies have shown that polysaccharides can interact directly or indirectly with immune cells, which in turn prompts various cellular or molecular reactions. These reactions activate the immune system and ultimately result in immunomodulatory effects. Furthermore, the immune system can recognize and target a wide range of antigens and harmful substances produced by tumor cells in the body. This recognition leads to the elimination of these malignant cells. Therefore, it is highly likely that polysaccharides with immunomodulatory properties may be promising and potent antitumor drugs [42]. [PERSON] et al. isolated SPPs with antitumor and immune-enhancing activities from Sargassum, which could enhance the proliferation of immune cells and increase the expression of serum cytokines, and further analysis showed that it could significantly induce apoptosis while inhibiting the normal physiological process of cancer cells, suggesting that SPPs, polysaccharides isolated from the natural polysaccharide Sargassum, are involved in immune-regulatory effects in various ways and can be used as potential bioactive components of antitumor drugs with immune-enhancing activities [43]. Further research and analysis of the antitumor and immune-enhancing activities and structural features of SPPs are still needed, and secondly, according to the antitumor mechanism of the SPP-0.7 fraction pointed out by the authors in the article, more experiments need to be conducted in the future for validation. This is the first study of the antitumor and immune-enhancing activity of SPPs, which could contribute to the further development of this traditional Chinese herb and seaweed, but in the meantime, further analysis of its structure is still needed. Polysaccharides from Chinese herbs have been found to induce apoptosis in various tumor cells, both in vivo and in vitro. For example, Dendrobium polysaccharides, Astragalus polysaccharides, Lycium barbarum polysaccharides, and panax notoginseng polysaccharides have shown this effect [44; 45; 46; 47]. Polysaccharides from food sources, such as coriander polysaccharides, pomegranate polysaccharides, chestnut polysaccharides, and papaya polysaccharides, also demonstrate antitumor effects [48; 49; 50; 51]. The relative molecular mass distribution of polysaccharides, the composition of sugar groups, the type of glycosidic bonding and the way adjacent glycosidic bonds are connected, the presence or absence of branched chains as well as their position and length, and the non-sugar modifications may have a significant effect on their activity, as shown in Figure 2. Astragalus polysaccharides (APSs) with different Mw values stimulate the proliferation of macrophage-absorbing neutrophil erythrocytes and NK cells to varying degrees, which in turn modulates the intensity of nonspecific immune responses [52]. Different structures and modifications of polysaccharides enable different polysaccharides to have various biological activities, such as antitumor and antioxidant.