CD4 and COVID-19: The number of CD4+ Th cells in the peripheral blood significantly decreased, but the plasma levels of inflammatory cytokines significantly increased in patients with COVID-19; this finding may be related to the increased secretion of TNF-α and IL-6 by a large number of immune cells other than CD4+ Th cells in the peripheral blood or the enhanced ability of single CD4+ Th cells to secrete TNF-α and IL-6 during 2019-nCoV infection.