TLR4 and COVID-19: TLR2, MMP9, FPR2, CSF1R, and C5AR1 expressions in COVID-19 were positively correlated with eosinophils, immature dendritic cells, macrophages, neutrophils, plasmacytoid dendritic cells, and Type 17 T helper cells (correlation > 0.75); TLR4 and CYBB expressions were positively correlated with Type 17 T helper cells and T follicular helper cells, suggesting their roles in regulating immunity (Figure 5D).