[Understanding rheumatoid arthritis]

Rheumatoid arthritis is a common and severe inflammatory rheumatic disease, for which the immune mechanisms are being decoded little by little. The pathogenic ncludes significant cellular actors of innate immunity (fibroblastic synoviocytes, macrophages, mastocytes...) and adaptive immunity (T and B lymphocytes). These actors interact through the production of and response to specific (cytokines, chemokines and auto-antibodies) and non-specific (prostaglandins, nitrous oxide [NO], complement, proteases) mediators. The chronology of this rheumatoid synovitis is becoming progressively clearer. Its initiation could be the consequence of a precocious activation of the innate immunity, induced by bacterial agents or debris (PAMP). The activation of the synoviocytes and the macrophages via specific receptors (PPR) unleashes an intense inflammatory reaction that triggers a cascade of events. The ongoing nature of this synovitis leads to the intra-articular recruitment of different cells of immunity. This cellular afflux amplifies the macrophagic and synoviocytic activation and proliferation. All of these interactive phenomena end in the production of large quantities of pro-inflammatory cytokines (TNFa, IL1, IL6, IL15, IL17, IL18) but also other pathogenic mediators (auto-antibodies, complement, prostaglandins, nitrous oxide...). This synovitis persists, as it is no longer regulated by a sufficient production of physiological regulators (soluble receptors and inhibitors of cytokines). The consequence of this intense inflammation and synovial proliferation leads to osteo-articular destruction by the production of proteases and the activation of osteoclasts by the RANK/RANK-ligand pathway under the effect of cytokines (TNFa, IL5, IL1, IL6, IL17) and other mediators (prostaglandins) liberated by synoviocytes, macrophages and lymphocytes. The decryption of this puzzle has already created new therapeutic orientations. The identification of new targets is one of the major consequences of this progress in immuno-rheumatology.