Colonization of nasal cavities by Staphylococcus epidermidis mitigates SARS-CoV-2 nucleocapsid phosphoprotein-induced interleukin (IL)-6 in the lung.

Infection by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can trigger excessive interleukin (IL)-6 signalling, leading to a myriad of biological effects including a cytokine storm that contributes to multiple organ failure in severe coronavirus disease 2019 (COVID-19). Using a mouse model, we demonstrated that nasal inoculation of nucleocapsid phosphoprotein (NPP) of SARS-CoV-2 increased IL-6 content in bronchoalveolar lavage fluid (BALF). Nasal administration of liquid coco-caprylate/caprate (LCC) onto Staphylococcus epidermidis (S. epidermidis)-colonized mice significantly attenuated NPP-induced IL-6. Furthermore, S. epidermidis-mediated LCC fermentation to generate electricity and butyric acid that promoted bacterial colonization and activated free fatty acid receptor 2 (Ffar2) respectively. Inhibition of Ffar2 impeded the effect of S. epidermidis plus LCC on the reduction of NPP-induced IL-6. Collectively, these results suggest that nasal S. epidermidis is part of the first line of defence in ameliorating a cytokine storm induced by airway infection of SARS-CoV-2.

Gut probiotic Lactobacillus rhamnosus attenuates PDE4B-mediated interleukin-6 induced by SARS-CoV-2 membrane glycoprotein.

Membrane glycoprotein is the most abundant protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but its role in coronavirus disease 2019 (COVID-19) has not been fully characterized. Mice intranasally inoculated with membrane glycoprotein substantially increased the interleukin (IL)-6, a hallmark of the cytokine storm, in bronchoalveolar lavage fluid (BALF), compared to mice inoculated with green fluorescent protein (GFP). The high level of IL-6 induced by membrane glycoprotein was significantly diminished in phosphodiesterase 4 (PDE4B) knockout mice, demonstrating the essential role of PDE4B in IL-6 signaling. Mycelium fermentation of Lactobacillus rhamnosus (L. rhamnosus) EH8 strain yielded butyric acid, which can down-regulate the PDE4B expression and IL-6 secretion in macrophages. Feeding mice with mycelia increased the relative abundance of commensal L. rhamnosus. Two-week supplementation of mice with L. rhamnosus plus mycelia considerably decreased membrane glycoprotein-induced PDE4B expression and IL-6 secretion. The probiotic activity of L. rhamnosus plus mycelia against membrane glycoprotein was abolished in mice treated with GLPG-0974, an antagonist of free fatty acid receptor 2 (Ffar2). Activation of Ffar2 in the gut-lung axis for down-regulation of the PDE4B-IL-6 signalling may provide targets for development of modalities including probiotics for treatment of the cytokine storm in COVID-19.