Beneficial autoimmunity participates in the regulation of rheumatoid arthritis

Abstract

Antigen specific T cells and B cells recognize their target determinants by antigen specific receptors that are being rearranged in a random manner. These cells then undergo negative and positive selection processes that limit, albeit not eliminate, the escape of self-reactive T and B cells capable of eliciting autoimmune responses. The above processes are referred to as "central selection", and their outcome is the "central tolerance". Auto-reactive T and B cells escaping central tolerance are then subjected to peripheral mechanisms that restrain their auto-aggressive behavior. Different types of regulatory T cells are key players in maintaining actively induced peripheral tolerance. In patients suffering from various autoimmune disorders autoreactive T and/or B cells that escaped central tolerance also circumvented regulatory T cells that could, potentially, eradicate their pathogenicity in the periphery. We have found an additional regulatory mechanism that restrains the harmful activity of these cells at that time. It includes autoimmune B cells that produce neutralizing autoantibodies against numerous inflammatory mediators, mostly cytokines and chemokines, which participate in destructive autoimmunity. These autoantibodies restrain the harmful consequences of inflammatory autoimmune conditions such as in rheumatoid arthritis. Interestingly, this antibody production is elicited during autoimmune diseases, and to a much lesser extent during local inflammation. The specificity of this response is highly restricted to determinants with minimal cross reactivity to other known gene products. Thus, the immune system allows selective breakdown of tolerance in autoimmune conditions. The findings that this beneficial response is turned on by the autoimmune condition, and then regulated by its progression further imply for the existence of a programmed regulatory response of "beneficial autoimmunity". In the current review we describe how this mechanism was discovered in experimental models of rheumatoid arthritis and multiple sclerosis, demonstrate its importance in the natural regulation of these diseases, and finally explore its relevance to human diseases.