The lymphopenia of COVID-19 patients includes CD4 + T cells, CD8 + T cells, B cells, and natural killer (NK) cells, with the damage of CD8 + T cells being more significant . No obvious virus infection is detected in lymphocytes and mesenchymal cell . Lymphopenia at the initial appearance of COVID-19 is associated with poor prognosis . Lymphopenia and its severity are reliable predictors of the clinical outcome of COVID-19, including mortality, intensive care needs, and oxygen requirements . Besides, the high fatality rate of COVID-19 is related to the poor performance of MHC II and the low coverage of MHC II . The quality of MHCII presented by T cells is an essential prerequisite for T cell-dependent antibody production. The binding capacity of MHC-I epitope load and SARS-COV-2 peptide affects the immunity of T cells to infection . Therefore, MHC presentation is closely related to lymphopenia of COVID-19.