Evidence suggests that the S1 subunit can travel along nervus neurons terminals and its axons to the brain and then activate microglia by binding to TLR4, resulting in increased expression of pro-inflammatory cytokines such as IL1β and antigen-presenting molecules such as MHC-II – molecules upregulated in post-mortem brains of COVID-19 patients. This evidence concerns the gene TLR4 and COVID-19.