Surface antigens on peripheral blood eosinophils from 23 patients with bronchial asthma, 6 with eosinophilic pneumonia and 8 controls were examined using a new direct method. Peripheral blood eosinophils in bronchial asthma and eosinophilic pneumonia showed higher complexity and/or granularity than those from controls. The percentage expression of HLA DR, CD4 and CD45RO on peripheral blood eosinophils from patients with bronchial asthma were increased compared with those from patients with eosinophilic pneumonia and from the controls. These results suggest that peripheral blood eosinophils in bronchial asthma may play a role in immunoregulation via the expression of human leukocyte antigens, such as HLA-DR, CD4 and CD45RO, that interact with lymphocytes, and may function as antigen-presenting cells. Furthermore this study suggests that there may be different phenotypes of eosinophils with differing surface antigens and intercellular reactions between eosinophils and lymphocytes.

Bronchoalveolar lavage was performed in patients with chronic eosinophilic pneumonia of unknown origin diagnosed histopathologically, and the alveolar fluid cells were investigated before and during corticosteroid therapy. The counts of eosinophils in bronchoalveolar lavage fluid decreased markedly during steroid therapy compared with before therapy, and the ratios of interleukin 2 receptor-positive T cells and HLA DR-positive T cells to all T lymphocytes in the lavage fluid also decreased. Both before and during steroid therapy, many macrophages in bronchoalveolar lavage fluid phagocytosed EG2-positive granules and stained immunohistochemically as CD71-positive ‘responsive macrophages’. The decrease of activated T lymphocytes and the active phagocytosis of eosinophil granules by macrophages might play an important role in the mechanism of healing in chronic eosinophilic pneumonia.

Recent studies have suggested that there may be heterogeneity among human eosinophils. To study this further, surface antigens on blood eosinophils from patients with eosinophilia (23 bronchial asthma, 6 eosinophilic pneumonia, 1 Kimura’s disease and 1 adult T-cell leukemia) and from 8 control subjects were examined using a new direct method for fluorescence detection of eosinophils. HLA-DR+ and CD4+ eosinophil counts were higher in patients with bronchial asthma and adult T-cell leukemia (ATL) than in patients from other groups and in control subjects. CD1 lb+ eosinophil counts in Kimura’s disease and ATL were smaller than those in the other groups. CD45RO+ eosinophil counts in bronchial asthma and eosinophilic pneumonia were significantly higher (p < 0.05) compared with Kimura’s disease, ATL and control subjects. CD44+ eosinophil counts in eosinophilic pneumonia were significantly higher (p < 0.05) compared with the other groups and control subjects. These results suggest the existence of functional heterogeneity in the different eosinophilic diseases, with eosinophils in bronchial asthma and eosinophilic pneumonia being more highly activated in migration, activation and immunoregulation. On the other hand, eosinophils in Kimura’s disease and ATL might be functionally down-regulated. This heterogeneity of eosinophils may reflect differences in the pathogenesis of various eosinophilic diseases.

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