Innate immune responses in COVID-19

Innate immunity is the first line of host defense against microbes, including SARS-CoV-2. This pleiotropic immunological mechanism is initiated within minutes to hours after infection. Here, we summarize innate immune processes involved in SARS-CoV-2 recognition, cellular, and molecular response including inflammation, as well as the related immune modulatory therapies that have been evaluated in clinical trials for COVID-19. Innate immune responses limit viral replication, help identify and remove infected cells, sense pathogen-associated molecular patterns, trigger signaling pathways, inflammatory responses, cytokine production, programmed cell death, and contribute the development of adaptive immunity. Excessive activation of the host innate immune response is associated with severe disease and death. The availability and speed of implementation of these mechanisms in infected individuals may explain in part the heterogeneous disease spectrum and courses observed in patients.