Immunoelectron microscopic localization of catalase in human eosinophilic leukocytes

The immunologic localization of catalase in human eosinophilic leukocytes was studied by use of rabbit anti-human erythrocyte catalase (aHEC) antiserum. Indirect immunofluorescence studies revealed intense localization of fluorescence in the cytoplasm of the eosinophils with a pattern of distribution corresponding to that of the eosinophil granules. Control samples and other nucleated blood elements remained essentially unreactive. Immunoelectron microscopy using aHEC coupled to protein A-gold complexes revealed that catalase was present exclusively within the cytoplasmic granules and equally distributed over the paracrystalline body and the homogeneous granule matrix. The presence of catalase within the paracrystalline body has not been demonstrated before with conventional cytochemical techniques. The results raise the possibility that catalase is stored in the paracrystalline body in an inactive or latent form readily available during eosinophil activation and granule release.