XAF1 and COVID-19: In addition, the activation of various apoptosis-associated pathways (e.g., FAS-induced apoptosis pathway) could also contribute to lymphocyte depletion.25 Consistently, various pro-apoptotic molecules (e.g., CASP3, FAS, FASLG and XAF1, etc.)were highly expressed in the COVID-19 AE group, implying that cell apoptosis might be related to lymphopenia observed in patients with AE.