CD38 and COVID-19: However, some studies demonstrated that these NK cells overexpressed several markers related to a dysfunctional phenotype in severe COVID-19, like CD39 [44], PD-1 [44, 45], NKG2A [44, 46], DUSP2 [47], CD69 [45, 47], CD38 [47], LAG-3 [45] and TIM-3 [45].