The role of eosinophils in necrosis mainly in single-system Langerhans cell histiocytosis

Background: Single-system Langerhans cell histiocytosis (LCH) shows massive infiltration of eosinophils and occasional necrosis and cyst/cavity formation, but the cause of the necrosis remains unclear.The role of eosinophils in necrosis in single-system LCH has not been examined yet, and therefore,we investigated their role pathologically. Methods: Biopsy/lobectomy specimens were collected in 49 cases (50 lesions, 30 males, 19 females; mean age 31 years) satisfying the pathological criteria of LCH from 22 institutions from the beginning of 1998 to the end of 2011. Sources of organs were 33 lungs and 17 other organs. Forty-seven cases showed single-system LCH and 2 cases showed multiple-system LCH without involvement of “Risk Organs”. The interrelationship between eosinophils and necrosis, various kinds of tissue destruction, and subsequent findings were investigated. Cellular features of the earliest LCH lesion were also examined in detail. Ordinal histopathological and immunohistochemical examinations that included anti-eosinophilic antibodies were used. Results: Destructive features and subsequent findings of pulmonary LCH from 30 cases were as follows: vascular destruction, 6; cyst/cavity formations, 22; filling of tissue defect, 15;and elastic tissue, 30,and reticuline fiber destruction, 17. Tiny necroses accompanying degranulation of dead eosinophils without fibrosis werepresent in 2 cases. Large numbers of Langerhans cells and eosinophils were observed in the cellular-stage lesions and were associated with each other. Destructive features and subsequent findings of non-pulmonary LCH from 17 cases were as follows: coagulative necrosis of various extent without fibrosis, 8; cavity formation and cell shedding, 5; and reticuline fiber network destruction, 15. Large numbers of dead eosinophils accompanying degranulation were noted in most of the necrotic lesions along with a few Charcot-Leyden crystals. Degranulation of neutrophils in the necrotic lesions was limited to live cells. Conclusions: These findings suggest an intimate relationship between preceding degranulation of eosinophils in necrosis and various kinds of tissue destruction following necrosis in LCH.