CD4 and rheumatoid arthritis: A reduced thymic activity was one of the common clinical features in patients suffering from different autoimmune diseases, namely, rheumatoid arthritis (RA) (11, 12) with a lower TREC number especially in isolated CD4+ T cells (13), multiple sclerosis with a decrease in TREC frequencies in both CD4+ and CD8+ T cells (14, 15), systemic lupus erythematosus (SLE) (15–17), and myasthenia gravis (18).