TNF and juvenile idiopathic arthritis: What is more, the blood concentrations of the evaluated marker in the treated patients showing no clinical improvement (B’, active disease) were statistically higher, as compared to the TNF-α serum level in both the healthy children (p = 0.0000, by 79%) and in the patients with JIA who were not subjected to the therapy (B, p = 0.0063, by 27%), as well as the treated patients with inactive JIA (A’, p = 0.0001, by 70%) (Table 2).