Eosinophilic granuloma of the bone in Hand-Schüller-Christian disease: extensive in vivo eosinophil degranulation and subsequent binding of released eosinophil peroxidase (EPO) to other inflammatory cells.

The eosinophils from bone granuloma, bone marrow, and peripheral blood of a patient with Hand-Schüller-Christian disease (HSCD) were studied by electron microscopy and cytochemistry. Impressive eosinophil degranulation was observed. Extracellular release of eosinophil peroxidase (EPO) and EPO binding to surrounding cells were seen in the granuloma and bone marrow. Cells with peroxidase-positive plasma membrane were also observed in peripheral blood. The pattern of eosinophil degranulation showed quite different features from those described so far. In the granuloma, the process begins with intracytoplasmic release of the granule matrix content, as revealed by both extensive extragranular accumulation of EPO and progressive decrease of the matrix electron density. Core dissolution follows thereafter, leading to complete disappearance of the granules. At the end of the process, the cells show rupture of the plasma membrane and release of their content into the surrounding environment. This pattern of secretion was also observed in blood and marrow eosinophils of the patient. In view of the previously reported findings that EPO binding to inflammatory cells influences their functions, EPO release and binding to surrounding cells in HSCD may play a role in the evolution of the inflammatory lesion in the disease.