For example, Lee et al., used scRNA-seq to examine peripheral blood mononuclear cells (PBMCs) from patients with influenza or severe COVID-19, reporting a common enrichment of inflammatory monocytes upregulating TNF-α, IL-1β, and IFN-I, alongside influenza-specific expression of STAT1 and TLR4 and COVID-19-specific expression of NFKB1/2 and STAT4 (Lee et al., 2020). Here, TLR4 is linked to influenza.