IL17A and COVID-19: Immune response analysis showed that COVID-19 strongly inhibited the secretion of IFN-1, related to excessive inflammation (160). Clinical studies have shown that the severity of COVID-19 positively correlates with the serum levels of several cytokines, including TNF-α, IL-6, IL-7, IL-17, IL-18, granulocyte colony-stimulating factor (G-CSF), IP10, macrophage colony-stimulating factor (M-CSF), and chemokines.