CXCL11 and influenza: In the BAL fluid of COVID-19 compared with critically ill influenza patients, we detected elevated and extremely high levels of the cytokines IL-1β, IL-1RA, IL-17A, TNF-α, and G-CSF and the chemokines CCL7, CXCL1, CXCL8, CXCL11, and CXCL12α, expanding earlier reports showing increased concentrations of inflammatory mediators compared with BAL fluid of healthy donors or patients with moderate influenza or COVID-19 (30–32).