HLA-DRB1 and COVID-19: The eight MHC class II gene expressions were significantly decreased in the KD group compared to FC, including HLA-DMA, HLA-DMB, HLA-DPA1, HLA-DPB1, HLA-DQA1, HLA-DRA, HLA-DRB1, and HLA-DRB5, as well as in severe COVID-19 compared to mild COVID-19 (Figure 5).