FIG. 5.

Oxidative stress during infection. In a balanced response found when a pathogen is eliminated by infected cells (A), initially there is a substantial increase in ROS generation, followed by a counter-response characterized by increased production of antioxidant molecules, which prevents excessive stress and damage. When a pathogen persists, the ROS production may increase incessantly over time. In this setting, the antioxidant responses could either fail to increase proportionally (B) or be insufficient to dampen the pathological oxidation regardless of its induction capacity (C). The persistent and unbalanced accumulation of ROS is called oxidative stress, and has important deleterious consequences in cell metabolism and viability.