Pre-stored mediators - Reactive Oxygen Species
Some molecules released during degranulation have a highly reactive chemical nature and interfere with proteins in pathogens to the extent that these then stop functioning. These include the reactive oxygen species (ROS) which are small highly unstable molecules produced as a direct result of pathogenic exposure in macrophages, neutrophils and eosinophils. A huge amount of oxygen is needed to make ROS which explains the term "respiratory burst" used to describe this process. Neutrophils and eosinophils have enzymes, myeloperoxidase (MPO) and eosinophil peroxidase (EPO) respectively, which generate more toxic ROS and which also are very toxic to host cells and cause cell damage. In allergic disease high levels of ROS derived from these cells are thought to contribute to tissue damage.
Another type of oxidant, called nitric oxide (NO), is also produced following pathogen exposure but unlike ROS this molecule is generated much later, up to hours after the interaction. What do you think would be the advantage of this time difference in release of ROS and NO? Think about the effect on the pathogen over time. Oxidants kill pathogens by interacting with key proteins important in their survival. However oxidants can also interact with our proteins. It is therefore lucky that we have anti-oxidants present both within cells and in the surrounding tissue that protect us by "taking the blow" from the oxidants like a bodyguard throwing itself into the line of fire to save its client. In allergy, levels of anti-oxidants and oxidants (both ROS and NO) are increased and neutrophils and eosinophils have an increased capacity for ROS generation, suggesting they are primed and ready to go!