CD8A and infection: One of these studies suggested that the activation of T cells is higher in the lungs than in peripheral blood [47], while other studies identified two different cell subpopulations of activated CD8+ T cells in the PBMCs of COVID-19 patients: HLA-DR+CD38dim cells, which are predominantly present in both mild and severe cases after 2 to 3 weeks of natural infection, and HLA-DR+CD38high cells, which are only found in severe cases [49].