IL15 and COVID-19: Similarly, we found that the expression pattern of STAT1-dependent cytokines and chemokines, including IL15, TNF-related apoptosis-inducing ligand (TRAIL), and B cell activating factor (BAFF), CCL2, CCL7, CXCL10, and CXCL11 in both PBMCs and monocytes increased with the severity of COVID-19, while CCL8 mRNA was significantly expressed in moderate COVID-19 patients but decreased in severe and critical COVID-19 patients.