Ultrastructural Observation of Eosinophils in Bronchoalveolar Lavage Fluid in Eosinophilic Pneumonia

: To investigate the morphological changes of local eosinophils in the lungs, we observed the ultrastructure of eosinophils in bronchoalveolar lavage fluid (BALF) from patients with eosinophilic pneumonia. We also measured the BALF concentration of eosinophil cationic protein (ECP) as an index of the activation of eosinophils. The eosinophils in BALF from patients with eosinophilic pneumonia showed various ultrastructural changes compared to eosinophils in BALF of the control patient. Changes included degranulation or disintegration of specific granules, cytoplasmic vacuolation, increased lipid droplets and the appearance of Charcot-Leiden crystals. These changes of BALF eosinophils were more prominent than those of peripheral blood eosinophils. ECP concentration (mean +/- SD) in BALF from patients with eosinophilic pneumonia was 12.2 +/- 7.78 micrograms/l which was significantly higher than the concentrations in patients with bronchial asthma not during an attack (1.36 +/- 2.08 micrograms/l) and in healthy control subjects (2.14 +/- 4.62 micrograms/l). These results suggest that local eosinophils in the lungs are activated and degranulated by various stimuli and undergo structural degeneration in eosinophilic pneumonia.