A current perspective on the role of eosinophils in dermatologic diseases

Eosinophils are frequently observed in cutaneous inflammation, but little is known of their significance in the pathophysiology of cutaneous disease. Recent studies of the structure, content, and activities of the eosinophil have shown that it has potent toxic proteins with the potential to mediate tissue damage. Furthermore, immunofluorescent localization of eosinophil granule proteins has shown that eosinophils disrupt in tissue and deposit toxic granule proteins. The deposition of granule proteins in several diseases is vastly out proportion to the number of identifiable cells and indicates that eosinophil involvement in cutaneous disease cannot be judged by the number of intact eosinophils in the tissue. Specifically, deposition of eosinophil granule proteins outside of eosinophils has been observed in eczematous lichenified disorders with elevated serum levels of immunoglobulin E, in urticarial and angioedematous disorders, and in bullous diseases. The structural, compositional, and functional characteristics of eosinophils are reviewed, and evidence of eosinophil degranulation in cutaneous diseases is presented. Mechanisms whereby eosinophil degranulation may mediate pathophysiologic effects are also discussed.