CD4 and autoimmune disease: Regarding the abnormal expression of HDAC4 in patients with autoimmune diseases, it has been revealed that HDAC4 is decreased in the synovial tissues from rheumatoid arthritis patients compared with those from healthy subjects (12); in addition, HDAC4 is also reduced in the CD4+ T cells and intestinal mucosa tissues in patients with inflammatory bowel disease compared with those from healthy controls (16).