# Important Roles of Oligo- and Polysaccharides
## 2 Oligo- and Polysaccharides against SARS-CoV-2  
Polysaccharides are polymeric carbohydrates that are formed naturally by various identical or different monosaccharide units (C\({}_{n}\)(H\({}_{2}\)O)\({}_{n}\)) connected via glycosidic bonds [5; 19]. SARS-CoV-2 deploys its vastly glycosylated trimeric spike protein to attach to the angiotensin-converting enzyme 2 (ACE2) glycoprotein on the cell surface receptor for facilitating entry into the host cell [20]; the transmembrane spike glycoprotein of CoVs exists as a homotrimic form, and it is covered with \(N\)-linked glycans. S glycoprotein is recognized as the main target of antibodies with a neutralizing potency, and it has been examined as an attractive target for therapeutic or vaccine development. The targeting of \(N\)-linked glycans of the S glycoprotein envelope of CoVs through carbohydrate-binding agents could serve as an attractive therapeutic strategy for developing innovative antivirals. Carbohydrate-binding agents from natural resources like lectins from plants, and marine algae and prokaryotes and lectin mimics like Pradimicin-A have exhibited antiviral performances against CoVs and other enveloped viruses. However, the potential application of carbohydrate-binding agents and lectins has been restricted because of unfavorable responses such as immunogenicity, mitogenicity, hemagglutinin, inflammatory activity, and cellular toxicity [21]. The mammalian's cell surface is coated with intricate glycans or polysaccharides where many viruses become attached [22]. These glycans on the cell surface, namely heparan sulfate proteoglycan, can enhance the host cells infection. Additionally, glycans on such cell surfaces function as receptors implicated in the transfer of signals induced by endocytosis or in the initiation of blending among the cell membrane and the viral envelope for certain viruses. Alternatively, the viral proteins can be glycosylated as viruses exploit the machinery of the host cell, thus affecting the function and stability of the viral glycoprotein while making an entry into the host cell. Further, it has been shown that viral glycoprotein glycosylation is implicated in viral antigenicity accountable for virus's immune avoidance [23]. Natural polysaccharides are sustainable, renewable, abundant, and environmentally friendly biopolymers readily available from diverse natural bioresources, namely animals (e.g., gelatin/collagen, silk, chitosan, hyaluronic acid, or hyaluron), plants (e.g., pectin, cellulose, and starch), algae (e.g., agar and alginate), and microorganisms (e.g., xanthan gum, dextran, and pullulan) [24; 25; 26; 27]. Polysaccharides from natural/edible origins can help modulate the immunity against SARS-CoV-2 via several pathways (Figure 2); glucans and chitosan can be utilized for the delivery of antigens on various platforms and in vaccine developments [28]. These polysaccharides retain different chemical structures, including branched or linear arrangements, diverse charge states (neutral, negatively or positively charged), varying chemical compositions (\(\alpha\) and/or \(\beta\)-glycosidic bonds among assorted monosaccharides units), and a wide range of molecular masses [29]. Polysaccharides represent promising potentials for pharmaceutical and biomedical applications, in terms of the chemical diversity of their structures, physicochemical and biological features, safety, high chemical reactivity, biocompatibility, renewability, low toxicity, and biodegradability. The high biocompatibility and biodegradability, as well as low/non-toxicity, of these mate rials contribute toward the enhancement of their biomedical appliances as immunogenicity depends on the individual structures [30; 31]. Polysaccharides have exhibited several attractive anti-CoVs effects, and they can be utilized in the form of vaccine adjuvants that are polysaccharide- and nano-based structures, and innovative drug conveyance systems versus these pathogenic viruses [8; 32; 33; 34].