CD28 and rheumatoid arthritis: (CIA Mice): Mice were treated with lentiviruses (LV-YY1-shRNA, LV-YY1, or LV-NC) via tail intravenous injection at a dose of (4 × 107)TU/mouse.PBMCs from RA patients: Infected with lentivirus in the presence of Dynabeads Human T-activator CD3/CD28 and IL-2 (10 IU/ml) for 48 hours.293T cells: Transfected with IL-6 promoter plasmids and then infected with lentivirus (LV-YY1-shRNA, LV-YY1, or LV-NC) at an MOI with (5 μg/ml) of polybrene.