HLA-DRB1 and COVID-19: Lastly, lungs of terminally ill COVID-19 patients also display a prominent reduction in the expression of several members of the major histocompatibility complex (MHC) class II, including HLA-DPA1, HLA-DRB1 and HLA-DRB5, all of which are reported to be reduced in antigen presenting cells of critically ill COVID-19 patients [27].