CD4 and hemorrhagic fever with renal syndrome: The ratio of CD3+ CD4+ T cells versus CD3+ CD8+ T cells in peripheral blood was determined by flow cytometry and found to be increased at 3 dpi and then rapidly reversed at 6 dpi, consistent with changes often observed in HFRS patients (Figure 3F), in whom CD4+ T cells dramatically decreased, and CD8+ T cells remain unchanged or compensatory expanded to result in a reversed ratio of CD4/CD8.