Although not studied in detail in COVID-19, it was shown in a previous study that class II MHC secretes different types of cytokines when binding to different peptides, thus triggering T cell differentiation in divergent ways (TH1/TH17 by DRB1*0401, risk; TH1/TH2 by DRB*0402, protective) in rheumatoid arthritis [40]. Here, HLA-DRB1 is linked to COVID-19.