TLR4 and COVID-19: This is consistent with previous results showing that S100A12 activates monocytes through TLR4 signaling.26 This signaling leads to the release of diverse pro-inflammatory cytokines via the MYD88 pathway.27 As expected, significantly elevated expression for MYD88 was also seen in COVID-19 acute necrotizing encephalopathy patients (Fig. 3f).