During severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, activated macrophages, dendritic cells (D.C.), neutrophils, and natural killer (N.K.) cells are the first defense against infection. These immune effectors trap and ingest the virus, kill infected epithelial cells, or produce anti-viral cytokines. Evidence suggests that aging, obesity, and mental illness can lead to weakened innate immunity and, thus, are all associated with elevated infection and severe disease progression of coronavirus disease 2019 (COVID-19). Innate immune defense networks play a fundamental role in suppressing viral replication, infection establishment, and viral pathogenesis of SARS-CoV-2 and other respiratory viruses.
