High proportion of inflammatory CD62Llow eosinophils in blood and nasal polyps of severe asthma patients.

BACKGROUND: In mice models, eosinophils have been divided into different subpopulations with distinct phenotypes and functions, based on CD62L and CD101 patterns of membrane expression. Limited data are available in humans. OBJECTIVE: To investigate eosinophils subpopulations in peripheral blood (PB) and nasal polyp tissue (NP) from severe eosinophilic asthma (SEA) patients plus concomitant chronic rhinosinusitis with nasal polyps (CRSwNP). METHODS: We recruited 23 SEA patients (14 with CRSwNP); as controls, we enrolled 15 non-severe asthma patients, 15 allergic rhinitis patients without asthma and 15 healthy donors. Eosinophils were isolated from PB and NP and analysed by FACS. Eotaxin-3 and eotaxin-1 mRNA expression in NP tissue was also evaluated. RESULTS: A significantly higher percentage of circulating CD62Llow cells was observed in SEA, as compared with controls, expressing higher levels of CCR3, CD69 and lower levels of CD125 (IL-5R), CRTH2, CD86 and CD28 in comparison with CD62Lbright cells. In NP, eosinophils showed a high proportion of CD62Llow phenotype, significantly greater than that observed in PB. Surface expression of IL-3R, IL-5R, CD69 and CD86 was significantly higher in CD62Llow eosinophils from NP than in those from blood. Moreover, eotaxin-3 mRNA expression positively correlated with the percentage of CD62Llow cells in NP. CONCLUSION: Two different eosinophil subphenotypes can be identified in blood and NP of SEA patients, with a preferential accumulation of CD62Llow inflammatory cells in NP.