Pathogenesis of juvenile idiopathic arthritis

Although the term juvenile idiopathic arthritis (JIA) encompasses a heterogeneous group of diseases, they all share a common pathological hallmark: inflammation of the synovium. Highly activated T cells, monocytes, and neutrophils are attracted to the joint and secrete mediators that not only perpetuate inflammation but also may attenuate immune regulation. In the oligoarticular and polyarticular forms of JIA, which are thought to be autoimmune conditions, dysregulated adaptive immunity is a likely factor in disease pathogenesis; the nature of the interactions between T effector (Teff) cells and T regulatory cells (Treg) is probably a key factor in controlling disease progression. Factors that affect the frequency and function of Tregs and/or the sensitivity of Teffs to mechanisms of immune suppression will therefore impact on the disease course. In the systemic form of JIA, however, dysregulation of innate immune pathways appears more central to disease pathogenesis resulting in augmented levels of interleukins IL-1β‎, IL-6, and IL-18. In the end, a final, common pathological pathway in JIA is the activation of monocytes and neutrophils, which are the principal mediators of joint inflammation and damage. This is supported by the fact that the therapies that have targeted innate cytokine pathways have shown greater success in the treatment of JIA.