Although the plasma viral load gradually decreased during the chronic stage, long-term infection induced significant decreases in the CD4+ T cell count (Figure 1B), CD4+ to CD8+ T cell ratio (Figure 1C), and activated CD4+ T cell count (defined by HLA-DR expression) (Figure 1D), as well as an increase in exhausted CD4+ T cell count (defined by PD-1 expression) (Figure 1E). The gene discussed is CD4; the disease is infection.