PDCD1 and COVID-19: COVID-19 patients had higher PD-1 positive Th frequencies and higher PD-1 MFIs in both unstimulated (Figure 2E, MMR 1.24 for MFI fold changes, p = 0.005) and AfuLy-stimulated samples (Figure 2F, MMR 1.20 for MFI fold changes, p < 0.001).