PDCD1 and COVID-19: TH1-like cells from patients with mild COVID-19 exhibited a TH1 polarization state, characterized by upregulation of effector marker genes (PDCD1, CCL5, CXCR2, CCR2, GZMA/B, NKG7, PRF1, IFNG, and CCL4) (5, 63) and genes involved in effector function such as CXCR4, CXCL2, ANXA1, SOCS2 and LTB (5).