There was a significant increase in PD-1-expressing T-cell subsets during SS including PD-1+/CD4+ TCM (P = 0.0018) and PD-1+/CD4+ TEM (P = 0.0165) (Figure 5C, left panel and Figure 5E) as well as PD-1+/CD8+ TCM (P = 0.0270) and PD-1+/CD8+ TEM (P = 0.0106) (Figure 5C, right panel and Figure 5E) compared to before infection. Here, CD4 is linked to infection.