CD4 and Arthritis: Moreover, in all studies except one 14 that have investigated CD4+CD25+ Treg cells in the inflamed joints of patients with arthritis, the findings concur, showing that these cells are functionally intact and are fully capable of suppressing proliferation and cytokine production ex vivo 1, 2, 3, 4, 5, 6, 7, 25, 26, 27.