Chronic Eosinophilic Pneumonia and Idiopathic Bronchiolitis Obliterans Organizing Pneumonia: Comparison of Eosinophil Number and Degranulation by Immunofluorescence Staining for Eosinophil-Derived Major Basic Protein

To undertake additional assessment of the possible overlap between bronchiolitis obliterans organizing pneumonia (BOOP) and chronic eosinophilic pneumonia (CEP). We retrospectively reviewed open-lung biopsy specimens from six patients with CEP, five patients with idiopathic BOOP, and four patients with secondary BOOP, encountered during the 5-year period 1986 through 1991, for the presence of eosinophils and extent of eosinophil degranulation. Using previously described immunofluorescence methods for detection of intact eosinophils and extracellular deposition of eo-sinophil-derived major basic protein, we counted the number of eosinophils per ×160 microscopic field and evaluated the extent of eosinophil degranulation semiquantitatively. The median numbers of eosinophils were 221 (range, 26 to 343) in cases of CEP, 7 (range, 1 to 65) in cases of idiopathic BOOP, and 7.5 (range, 1 to 39) in cases of secondary BOOP. More eosinophils were found in CEP than in idiopathic BOOP or all cases of idiopathic and secondary BOOP. We found no differences in the extent of eosinophil degranulation among the three groups, although a tendency for more degranulation was noted in cases of CEP. Even though clinical and histologic overlap may exist between CEP and idiopathic BOOP, the exact relationship and the role of the eosinophil in idiopathic BOOP remain to be determined.