In patients with COVID-19, the level of Treg cells (CD3+CD4+CD25+ CD127low+) decreases (Wang et al., 2020; Qin et al., 2020), the level of Th17 cells (CCR6+ Th17) increases, and the ratio of Treg/Th17 cells decreases (Wu and Yang, 2020). Here, CD4 is linked to COVID-19.