IL6 and COVID-19: As severe COVID-19 illness with neurological complications is characterized by neuroinflammation (including perivascular immune infiltrates, local activation of neuroglia, elevated inflammatory markers or cytokines, i.e., IL-6 and TNF-a in the cerebrospinal fluid) [39,51], the additive effect of TNF-a on the SH-SY5Y infection paradigm was tested.