CD4 and rheumatoid arthritis: Thymus degeneration is a frequent occurrence in patients with RA, often accompanied by incomplete thymic enlargement followed by deficient thymic output, which is significantly associated with the proportions of CD4+ effector memory T cells, IL-7, Thymosin β (Tβ) 4, IL-9, Th9, and thymic stromal lymphopoietin (TSLP) [62,63,64,65].