Ultrastructural study of tissue eosinophils on digestive biopsy with histologic GVHD.

(A) Eosinophils showing moderate signs of activation. Most cytoplasmic granules are altered and have characteristic crystal-shaped central cores that either disappear or are of diminished intensity (white arrows) compared with the few remaining normal central cores (black arrows). However, the cytoplasm is not disintegrated, and there are no cytoplasmic granules in the extracellular space. Epon embedding; bar = 1 μm. (B) Eosinophil showing signs of important in situ activation; the cytoplasm is partially disintegrated, and eosinophil granules are found in the intercellular space. Staining with an antibody directed against eosinophil peroxidase shows gold particles in the matrix of eosinophil granules, whether intracytoplasmic (white arrow) or extracellular (black arrow). Lowicryl HM20 embedding, indirect immunogold staining with an antibody directed against eosinophil peroxidase; bar = 1 μm. (C) Activated eosinophil synthesizing IL-5. Immunogold labeling with an antibody directed against IL-5 shows gold particles in the matrix of cytoplasmic granules (white arrows) in the extracellular space (black arrows) and in damaged extracellular granules. Lowicryl HM20 embedding, indirect immunogold staining with an antibody directed against IL-5; bar = 1 μm.