CD74 and COVID-19: Comparing with patients of COVID‐19 showing severe symptoms, the antigen processing and presentation pathway was increased and 12 typical genes, HLA‐DRB5, HLA‐DRB1, CD74, HLA‐DRA, HLA‐DPA1, HLA‐DQA1, HSP90AA1, HSP90AB1, HLA‐DPB1, HLA‐DQB1, HLA‐DQA2, and HLA‐DMA, particularly HLA‐DPB1, were obviously up‐regulated in ACE2‐positive bronchial epithelial cells of patients with mild disease.