CD4 and rheumatoid arthritis: Faulty activation or inadequate regulation of CD4+ and CD8+ T cells may contribute to the initiation and progression of multiple autoimmune diseases, including type 1 diabetes (T1D), rheumatoid arthritis (RA), autoimmune thyroiditis, systemic lupus erythematosus (SLE), multiple sclerosis, psoriasis, inflammatory bowel disease, as well as allergy and asthma [4,5].