TGFB1 and polyarticular arthritis: An association of the development of an increased level of TGF-β1 content with the duration of the active stage of JIA ≥ 4 years (OR = 6.11; 95% CI: 2.01-18.58; p<0.01), an increase in ESR (OR = 4, 33; 95% CI: 1.35-13.88; p<0.05), polyarthritis (OR = 3.74; 95% CI: 1.12-12.51; p<0.05), arterial hypertension (OR = 6.33; 95% CI: 1.36-29.55; p<0.05).