CD4 and hemorrhagic fever with renal syndrome: During the acute phase of the disease, the percentage of CFSEdim CD4+T cells showed a significant inverse correlation with the maximum plasma viral load in each HFRS patient (Fig 7E; P = 0.0435, r = −0.4556), suggesting that the acquisition of proliferative potential and capacity might be an essential character for specific CD4+T cells in protection from HTNV infection.