H2AB1 and autoimmune disease: To understand the underlying reasons for this phenomenon, we investigated specific downregulated genes in pathways associated with these four autoimmune diseases and found that the expression levels of class II histocompatibility antigen-related genes (H2-Aa, H2-DMb2, H2-DMa, H2-Eb1, H2-Ab1, and H2-DMb1) were significantly downregulated.