PDCD1 and COVID-19: To explore the mechanisms of decreased expression of PD-1 in CD4+ and CD8+ T cells from convalescent COVID-19 patients, we measured plasma cytokines associated with PD-1 expression, including IL-2, IL-6, IL-7, IL-10, IL-12p70, IL-33, IFN-γ and CCL19/MIP-3, by Luminex.