Immunoregulatory Roles of TGF-β and IL-4 during Mouse-adapted SARS-CoV-2 Infection

Abstract

Abstract Severe COVID-19 is due to a dysregulated immune response; however, the mechanisms preventing recovery of airway function are unclear. Cytokines regulate the quality of inflammation, and drive both anti-viral and disease tolerance mechanisms. There was a mostly monocytic infiltration in the lungs with alveolar thickening and consolidation 3 days post-infection with mouse-adapted SARS-CoV-2 (CMA3p20) at the peak of weight loss. Based on the cytokine profiles observed in human and animal studies, we targeted IL-4 and TGF-β as potentially regulatory cytokines, and quantified changes using flow cytometry. Neutralizing TGF-β, which regulates inflammatory cytokine production, significantly increased cellular infiltration of the lung. Neutralization of TGF-β particularly affected inflammatory monocyte (Ly6C+) recruitment, with a slight decrease in alveolar macrophages (CD11c-int). Neutralizing IL-4 prolonged weight loss to 4 dpi but visibly improved resolution of alveolar thickening on 7 dpi, suggesting that IL-4 is protecting from prolonged peak pathology, but delaying resolution. Neutralizing IL-4 also increased the fraction of polymorphonuclear cells and Tregs, as well as improving the ratio of type II to type I alveolar epithelial cells in the lungs compared to the isotype group. To begin to understand mechanisms connecting IL-4 to epithelial repair, we are studying the quality of the monocyte response and found alternatively activated macrophages with Ym1 staining in activated macrophages in the alveoli of infected mice in an IL-4 dependent manner. In order to improve therapeutics for severe COVID-19, it will be important to determine the cellular mechanisms linking regulatory cytokines to epithelial repair. R01AI135061 (RS, LPC), R01AI166668 (RR, MGO), R01AI131634 (MCS, HGF)