TNF and juvenile idiopathic arthritis: Increased inflammatory process, observed in the course of JIA, which develops as a result of excessive activity of pro-inflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1), IL-6, as well as reactive oxygen species (ROS) may contribute to proteolysis of core proteins of PGs, as well as the partial depolymerization of GAGs chains.