Current perspectives in reactive arthritis.

Reactive arthritis (ReA) is an inflammatory arthritis triggered by infection, usually urethritis or gastroenteritis, and is strongly associated with the MHC class I antigen HLA-B27. Two recent observations have excited interest: first, antigen and DNA from the triggering bacteria have been identified in the joint and, second, ReA synovial T cells have been found to respond specifically to the bacterium that caused the initiating infection. Because the trigger of ReA, its onset and the MHC association are all clearly defined, we can investigate hypotheses that are impossible to study in other forms of human arthritis. Here, Gabrielle Kingsley and Jochen Sieper review the topic in the light of a recent workshop.