IL-33 promotes inflammatory responses and exacerbates lung pathology in a mouse model of SARS-CoV-2 infection

Abstract The ongoing COVID-19 pandemic caused by SARS-CoV-2 has resulted in more than 6.6 million deaths worldwide as of the end of 2022. Clinical data revealed that dysregulated host immune responses may contribute to disease severity and poor recovery outcomes; however, the mechanisms that underlie immune dysregulation and disease severity are relatively unknown. Interleukin-33 (IL-33), a damage-associated molecular pattern (DAMP) molecule, is mainly expressed in nucleus of epithelial and endothelial cells. Elevated serum IL-33 levels have been recently reported in COVID-19 patients and might be associated with adverse outcomes. In this study, we infected B6 mice with a mouse-adapted SARS-CoV-2 MA10 and found that IL-33 was significantly increased in the lungs at day 2 post-infection, accompanied by highly upregulated inflammatory chemokines CXCL1, CXCL2 and CCL2. Next, we used IL-33−/− mice and demonstrated that IL-33 deficiency resulted in less bodyweight loss at days 2 and 3 and decreased viral burden at day 4. Flow cytometry analyses showed that IL-33−/− mice had reduced numbers of innate immune cells at day 2, including neutrophils, macrophages and NK cells. At day 4, IL-33−/− mice displayed reduced activated T cells in the lungs as compared to WT mice. Lung tissue RNAseq transcriptomics revealed that IL-33 signals contributed to several inflammatory pathways, including type II interferon signaling, pathogen phagocytosis, macrophage activation, cytokine/chemokine and inflammatory responses and oxidative damage. Overall, these data uncover a detrimental role of the DAMP IL-33 in the lungs following SARS-CoV-2 infection and provide new insights to support the development of effective therapeutic strategies for COVID-19. Supported by grants from NIH (R21 AI153586)