6  Conclusions & future perspectives
Polysaccharides have a long history to be used as important active ingredients in traditional Chinese medicine due to their extensive activity and reliable safety. Polysaccharides have broad spectrum of antiviral activities and unique antiviral mechanisms. They can exert antiviral effects by interfering with the life cycle of virus, or can indirectly exert antiviral activities by enhancing the body's immunity, which makes them have a great application prospect in anti-coronavirus. GAGs, marine polysaccharides such as carrageenan and chitosan, traditional Chinese medicine polysaccharides such as APS and LNT, and their derivatives, have shown potent anti-coronavirus activity and multiple anti-coronavirus mechanisms. We speculate that polysaccharides will exert anti-SARS-CoV-2 effects by the possible mechanisms as shown in Fig. 10 . More importantly, polysaccharide-based vaccine adjuvants, nanomaterials, and drug delivery systems will play important roles in anti-coronavirus field. Based on the immunomodulation and antiviral activity of polysaccharides, combined with nanotechnology, we put forward the strategy of loading S or N protein of coronavirus onto polysaccharide capped AuNPs vaccine for COVID-19 treatment (Fig. 9). This review may provide a novel idea for the development of anti-COVID-19 drugs and vaccines.
Fig. 10 The proposed mechanisms of polysaccharides anti-SARS-CoV-2.