PDCD1 and COVID-19: Similarly, large differences in PD-1 expression were detected between non-COVID-19 controls and ICU cases for CD4+PD-1+ T cells (median: 5.53% [IQR: 2.65–8.05] versus 29.08% [20.52–38.34%], respectively), CD8+PD-1+ T cells (3.76% [2.37–4.62%] versus 12.72% [6.76–16.76%], respectively), and CD19+PD-1+ B cells (1.82% [0.80–2.44%] versus 7.14 [3.97–12.10%], respectively).