IL6 and COVID-19: Accumulating evidence suggests that typical lymphopenia and cytokine release syndrome are two features that predict poor prognosis in COVID-19.3 In particular, the levels of blood interleukin-6 (IL-6) are closely correlated with the severity of COVID-19 and have been considered an independent biomarker for predicting poor prognosis.4 However, the sources and dynamics of increased IL-6 in COVID-19 patients remain largely unknown.