Eosinophils as effector cells in disease.

The ability of eosinophils to express Fc and C3b receptors can alter in vivo and in vitro, and with these membrane receptors eosinophils can bind to IgG or C3b coated metazoan parasites and cells, some of which are killed. In addition, IgG and C3b coated particles can induce eosinophils to secrete their granule contents which include distinct basic (cationic) proteins and peroxidase. These may bind to surfaces or cell membranes where they could initiate complement activation, coagulation or kinin generation. The high incidence of thrombi and endocardial cell damage in patients with persistent eosinophilia (even when it is induced by malignant disease), supports this possibility. Endocardial damage which leads to Löffler's cardiomyopathy may be induced by these products being secreted from circulating eosinophils which have a prolonged blood half-life in hypereosinophilic states. It is concluded that eosinophils have an active role in inducting inflammatory processes in tissues, and that they are important effector cells in some types of parasitic and allergic diseases. Analyses of the way in which these effects occur may show how eosinophils carry out their functions in tissues.