CD4 and COVID-19: By analyzing blood samples from COVID-19 patients and healthy donors, it was demonstrated that TfH (follicular helper CD4 T cells) and GCB (germinal center B) cells were significantly increased in patients with mild or moderate symptoms, while patients with severe COVID-19 showed lymphocyte dysfunction characterized by the severe depletion of CD4+ lymphocytes and subsequent B-cell lymphopenia [41].