Amelioration of lung inflammation induced with viral infectious stimulation by a high-molecular weight sulfated polysaccharide compound, Fucoidan mix-AG

Abstract

Abstract Fucoidan, viscous components in brown algae, has been reported to possess the effect enhancing cellular immune responses against cancer and viral infections. In contrast, it is also known to contribute to the alleviation of pathology in some inflammatory diseases, and almost certainly be effective in maintaining mucosal immune homeostasis. In this study, we evaluated the mitigating effect of fucoidan on pneumonia in aggravated upper airway infection. Consequently, C57BL/6J mice were orally administered 30 mg of Fucoidan mix-AG (Fm-AG) daily for 2 weeks, and then a solution of TLR ligands (TLR3-L: 62 µg Poly(I:C), TLR4-L: 25 µg rSARS-CoV-2 spike protein, TLR7-L: 5 µg Gardiquimod) were injected via oropharyngeal aspiration to simulate lung inflammation in viral infections. As a result, enhanced cellular infiltration into bronchoalveolar lavage (BAL) fluid were observed after the treatment with TLR ligands, but the expression of class II MHC molecules on the leukocytes was reduced in the Fm-AG-administrated mice as compared with the control mice. In addition, the markedly augmented production of inflammatory cytokine IL-6 in the model mice were significantly lowered by administration of Fm-AG both in BAL fluid and plasma. However, no reduction in the level of anti-viral IFNs were observed in the mice administrated Fm-AG. These results suggested that continuous intake of Fm-AG would prevent the severe complications (pneumonia and cytokine storm) during upper airway infections.