[Chemical basis of nonspecific immunity]

Our knowledge on the nature and quantity of reactive O2 forms generated in phagocytes, particularly, in neutrophil leucocytes, and their role in nonspecific immunity is reviewed. In thermodynamical terms, oxygen is a very reactive molecule and, hence, can react with most chemical elements and many organic molecules. In kinetic terms, O2 is rather inert. Its reactivity can be increased either by reduction or excitation. After accepting four electrons, O2 is finally reduced to H2O. Partial reduction resulting in highly reactive intermediates, namely, superoxide anion (O2.-), hydrogen peroxide (H2O2), and hydroxyl radical (.OH), is possible. Singlet oxygen (1O2) is the product of O2 excitation. Phagocytes acting like agents of nonspecific immunity generate such reactive forms of O2.