Lymphopenia, cell degeneration, necrosis, and atrophy are found in SARS and COVID-19 patients . The sort of lymphopenia and apoptosis between SARs and COVID-19 patients seems different. Namely, Lymphopenia in SARs patients precedes apoptosis, while apoptosis in COVID-19 patients precedes lymphopenia . The frequency and activation of SARS-COV-2 specific CD8 + T cells increase during severe illness, highlighting differences in T cell responses associated with disease progression . The number of regulatory T cells (Treg) has nothing to do with the severity of the disease, suggesting that T cell exhaustion occurs in a process independent of Treg . SARS-COV-2 generates ROS through the combination of E protein and heme , in which hydroxyl free radicals can directly destroy the cell membrane and cause damage to immune cells. Immune cells would be directly attacked along the route of antigen recognition and antigen presentation. So, CD4 + T cells, CD8 + T cells, and NK cells are most likely to be destroy and apoptosis in this link of binding to MHC molecules.