TLR7 and COVID-19: In this regard, it is interesting to observe how unvaccinated patients with homozygous mutations of the MyD88 or IRAK-4 genes have been associated with COVID-19 hypoxemic pneumonia resulting from reduced TLR7-dependent type I IFN production in plasmacytoid dendritic cells (pDCs), a subtype of immune cell otherwise known for the abundant secretion of interferon [78].