HAPLN1 and juvenile idiopathic arthritis: In order to achieve the main goal of the study, we assessed the relationship between the KS, HA and HAPLN1 plasma levels and the disease activity indicator, i.e., JADAS-27, as well as laboratory values of the inflammatory process indicators, i.e., CRP and ESR, in patients with JIA, both before biological treatment (T0) and after clinical improvement resulting from the applied ETA therapy (T24) (Table 3).