Apoptosis and phagocytosis of tissue-dwelling eosinophils in sinonasal polyps

Objective: Sinonasal polyps contain numerous tissue-dwelling eosinophils, b ut the mechanisms causing their accumulation, functional activities, and re solution are largely unknown. Study Design: Nasal polyp tissue from 14 pati ents was evaluated for cellular expression of CD95, CD68, and Annexin-V, fo r the degree of apoptosis, and for phagocytosis of eosinophils, Material an d Methods: Histological sections were immunostained as single stains for CD 95, CD68, and Annexin-V, and as an immunostaining for CD68 combined with a modified Vital New Red staining. The latter staining is specific for eosino phils. Other sections were stained by terminal d-UTP nick end labeling (TUN EL) assay and routinely stained for H&E. Evaluation of the amount of staine d cells was performed by counting the average number in 10 randomly chosen high-power fields. The TUNEL positivity was in all cases confirmed with apo ptotic morphology, Results: The inflammatory infiltrate consisted of numero us eosinophils but also a considerable amount of lymphocytes, mast cells, a nd macrophage-like CD68+ cells. CD95 was frequently expressed on eosinophil s, on numerous other inflammatory cells, and also on morphologically apopto tic cells. Annexin-V-positive eosinophils were not as frequent as CD95+ cel ls, but numerous Annexin-V-positive eosinophils were found. CD68+ cells app roximately equalled the number of eosinophils, The number of cells phagocyt osing eosinophils varied between polyps, Apoptosis of eosinophils (as evalu ated by TUNEL combined with apoptotic morphology) was a common finding in s ix of the polyps, Conclusions: Previous in vitro and ex vivo findings of CD 95 on eosinophils are now supported by demonstration of CD95 on eosinophils in this in vivo study. This investigation revealed a switch of the membran e-bound phosphatidylserine of apoptotic cells, which is a novel observation . The study has demonstrated apoptosis of tissue-dwelling eosinophils, and that CD68+ macrophage-like cells phagocytose eosinophils within the sinonas al polyps.