Sima, S. T.; Puebla-Clark, L.; Gonzalez-Orozco, M.; Endrino, M. J.; Shelite, T. R.; Tseng, H.-c.; Martinez-Martinez, Y. B.; Huante, M. B.; Federman, H. G.; Gbedande, K.; Menachery, V. D.; Siracusa, M. C.; Dann, S. M.; Endsley, J. J.; Rajsbaum, R.; Stephens, R.

The pathology of severe COVID-19 is due to a hyperinflammatory immune response persisting after viral clearance. To understand how the immune response to SARS-CoV-2 is regulated to avoid severe COVID-19, we tested relevant immunoregulatory cytokines. TGF-{beta}, IL-10 and IL-4 were neutralized upon infection with mouse-adapted SARS-CoV-2 (CMA3p20), a model of mild disease; and lung inflammation was quantified by histology and flow cytometry at early and late time points. Mild weight loss, and lung inflammation including consolidation and alveolar thickening were evident 3 days post-infection (dpi) and inflammation persisted to 7 dpi. Coinciding with early monocytic infiltrates, CCL2 and granulocyte-colony stimulating factor (G-CSF) were transiently produced 3 dpi, while IL-12 and CCL5 persisted to 7 dpi, modeling viral and inflammatory phases of disease. Neutralization of TGF-{beta}, but not IL-10 or IL-4, significantly increased lung inflammatory monocytes and elevated serum but not lung IL-6. Neutralization of IL-4 prolonged weight loss and increased early perivascular infiltration without changing viral titer. Anti-IL-4 reduced expression of Arg1, a gene associated with alternative activation of macrophages. Neutralizing TGF-{beta} and IL-4 had differential effects on pathology after virus control. Lung perivascular infiltration was reduced 7 dpi by neutralization of IL-4 or TGF-{beta}, and peri-airway inflammation was affected by anti-TGF-{beta}, while alveolar infiltrates were not affected by either. Anti-IL-4 prolonged IL-12 to 7 dpi along with reduced IL-10 in lungs. Overall, the immunoregulatory cytokines TGF-{beta} and IL-4 dampen initial inflammation in this maSARS-CoV-2 infection, suggesting that promotion of immunoregulation could help patients in early stages of disease.