P21 is also known as cyclin-dependent kinase (CDK) inhibitor 1. It is involved in the processes of apoptosis and cell cycle arrest and has been shown to block the activity of cyclin and CDK complexes in animal modules.
A study conducted by Mavers et. Al examined the potential P21 has in use relating to synovial inflammation that is consistent in animals with rheumatoid arthritis. In a previous study, Mavers et. Al found that in animals with rheumatoid arthritis there is decreased expression of P21 throughout the synovium, leading them to conclude that P21 has a suppressant effect on the inflammatory responses of the macrophages. This alludes to the idea that in the presence of P21 there will be less inflammation and tissue breakdown in the synovium.
The researchers of the initial study induced arthritis in mice that were lacking the expression of P21. From there, the next step was to treat the P21 knockout mice with a P21 mimetic which acted as a prophylactic for the development of arthritis in the mice. In the mice treated with P21 mimetic, the use of Luminex-based assays, flow cytometry, and ELISAs were used in order to observe LPS-induced cytokines and the signal transduction pathways throughout the macrophages in order to determine the strength of the inflammatory response in the presence of the P21 mimetic.