Researches make an incremental step forward in understanding the root causes of rheumatoid arthritis: "Untangling the root cause of rheumatoid arthritis has been a difficult task for immunologists, as decades of research has pointed to multiple culprits in our immune system, with contradictory lines of evidence. Now, [researchers] announce that it takes a diverse array of regulatory T cells (a specialized subset of white blood cells) to prevent the immune system from generating the tissue-specific inflammation that is a hallmark of the disease. Regulatory T cell diversity, the researchers say, provides a cumulative protective effect against rheumatoid arthritis. ... regulatory T cells (or Tregs) are a necessary component to either restrain (or encourage) the immune system's inflammatory response. Tregs are activated as molecules on their surface membranes called T cell receptors interact with 'friendly' or 'self' molecules - a way for the immune system to recognize friend from foe. Mismanagement of these Tregs, which normally serve to restrain the immune system from over-reacting to healthy tissue, could then lead to runaway inflammation. In this study, the researchers sought to examine how T cell receptors affect the ability of Tregs to suppress arthritis in a mouse that had been bred to express a 'self' molecule that drives arthritis. They showed that an array of Tregs given to the mice effectively stops arthritis. Unexpectedly, however, Tregs that are specific for the surrogate 'self' molecule do not prevent arthritis. ... We find that [a] diverse repertoire of Tregs are very effective. All of these Tregs, together, influence other components of the immune system which serves to slow down the inflammatory process that causes RA."