BTK and COVID-19: They are the primary sensor cells of PAMP through their PPR, which lead to increased intracellular BTK phosphorylation and NF-κB signaling in the context of COVID-19 [98], and are one of the most important sources of e.g. CXCL8, which is a potent chemoattractant for neutrophils (CXCL8 being overexpressed in high-viral-load COVID-19 [21]).