CD4 and COVID-19: Thus, to better understand the role of Tregs in the context of SARS-CoV-2 infection, we evaluated Tregs (CD3+CD4+CD25+FOXP3+) based on their frequency and expression of cytokines, cytotoxic granules, inhibitory receptors, and ectonucleotidases in the peripheral blood mononuclear cells (PBMC) from volunteers recovered from mild and severe forms of COVID-19.