Juvenile idiopathic arthritis (JIA) is a heterogeneous group of arthritis of unknown origin occurring in children under 16 years of age and persisting for at least 6 weeks. Given that JIA is an inflammatory disorder, treatment strategies, including also biologicals, are focused on suppressing excessive inflammation. The finding that different patients display different responses to biological drugs supports the concept that different pathogenic mechanisms can exist in JIA, with specific cellular and molecular mechanisms driving inflammation in each patient. The aim of this review is to highlight the most recent advances in understanding the role of immune cells in JIA pathogenesis.

This review encompasses the role of the different cell subsets involved in sustaining inflammation in JIA, with a particular emphasis on T cells, as they orchestrate both innate and adaptive auto-reactive immunity in affected joints.

The characterization of the cellular and molecular pathways supporting inflammation will be crucial to design novel therapeutic approaches in the context of personalized medicine.