We next studied the selected IFN gene expressions across five main leukocyte cell types in single cell RNAseq datasets (i.e. monocyte, B cell, CD4+ T cell, CD8+ T cell and NK cell) in COVID-19 cases and healthy controls at single cell and pseudobulk level (sum aggregation of single-cell RNA-seq data). The gene discussed is CD8A; the disease is COVID-19.