Figure 2.

During the adaptive immune response, immune cells of the T-helper (Th)1 type that have been activated create cytokines like interleukin-2 or interferon (IFN). In monocyte-derived macrophages (M), IFN-, a pro-inflammatory cytokine, stimulates the production of reactive oxygen species (ROS), as well as the action of indoleamine-2,3-dioxygenase (IDO) and GTP-cyclohydrolase I, which are both involved in the alteration of tryptophan to kynurenine and the production of neopterin, respectively. The creation of tumour necrosis factor (TNF), which increases macrophage receptivity to pro-inflammatory IFN, is triggered by the formation of ROS, which also activate redox-sensitive signal transduction cascades. When cells’ antioxidant defences are continuously overwhelmed by ROS, oxidative stress and inflammation result.