Role of eosinophil peroxidase in the origins of protein oxidation in asthma.

Eosinophils are uniquely endowed with an arsenal of enzymes that enable them to generate an array of reactive oxidants and diffusible radical species. The formidable arsenal at their disposal likely evolved because of the central role these phagocytes play in combating invading helminths and other large metazoan pathogens. Although these leukocytes constitute an essential component of the effector limb of host defenses, they also are implicated in contributing to inflammatory tissue injury. The growing prevalence and severity of asthma, a respiratory disease characterized by recruitment and activation of eosinophils in the airways of affected individuals, has focused research efforts on elaborating the many potential mechanisms through which eosinophils may contribute to tissue injury and oxidative modification of biological targets in asthma. Eosinophil activation is strongly suspected as playing a contributory role in the pathogenesis of asthma. Accordingly, an understanding of the basic chemical pathways available to the leukocytes for generating specific reactive oxidants and diffusible radical species in vivo is required. In the following review, recent progress in the elaboration of specific mechanisms through which eosinophils generate oxidants and other reactive species are discussed. The potential contributions of these intermediates to modification of biological targets during asthma are described. Particular emphasis is placed upon the secreted hemoprotein eosinophil peroxidase (EPO), a central participant in generation of reactive oxidants and diffusible radical species by the phagocytes.