Furthermore, pathways associated with adaptive immune responses were predominantly signaling pathways that contribute to the regulation of activated effector T-cell functions such as iCOS–iCOSL, Th1, protein kinase C-theta (PKC theta), calcium-induced T lymphocyte apoptosis and dendritic cell maturation pathways, which were downregulated in both severe- and mild-COVID-19 BAL cells (Figure 6a). This evidence concerns the gene ICOSLG and COVID-19.