TNF and COVID-19: For example, recent studies demonstrate that systemic inflammation induced by SARS-CoV-2, the etiologic agent of COVID-19, activates brain toll-like receptors (TLRs) and upregulates brain tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) signaling, triggering synapse damage and leading to depressive and cognitive symptoms in COVID-19 patients [15].