CD38 and COVID-19: To characterize whether stimulatory and inhibitory receptors are co-expressed on, or limited to distinct T cells we analyzed the expression of CD69 and the co-expression of HLA-DR/CD38 on PD1−LAG-3− and PD1−TIM-3− T cells and compared it to the expression on double-positive PD1+LAG-3+ and PD1+TIM-3+ T cells in COVID-19 and malaria patients.