CD19 and COVID-19: Greater than 10-fold differences in the expression of PD-L1 were observed between non-COVID-19 controls and ICU cases for CD4+PD-L1+ T cells (median: 1.92% [IQR: 0.98–3.91%] versus 22.49% [14.76–27.61%], respectively), CD8+PD-L1+ T cells (0.42% [0.29–0.67%] versus 18.38% [15.50–19.33%], respectively), and CD19+PD-L1+ B cells [0.20% (0.06–1.03%] versus 5.05% [3.00–11.19%], respectively).