Subsets of Eosinophils in Induced Sputum in Patients With Allergic Asthma Identified

While eosinophil subsets have previously been identified for asthma in blood samples, researchers have revealed that the subsets can also be identified in induced sputum using flow cytometry, according to a recent study.

The single center, observational, cross-sectional study included a total of 62 patients with persistent allergic asthma, of which 24 were eosinophilic, 18 mixed, 10 paucigranulocytic, and 10 neutrophilic. The researchers indicated that two subsets of eosinophils were defined as E1 (CD66b-high and CD15-high) and E2 (CD66b-low and CD15-low).

The researchers found that four phenotypes had detectable E1 and E2 subsets. E2 was comparable across the different phenotypes (p = 0.302), whereas E1 differed (p = 0.034). E1 predominated over E2 in patients with eosinophilic (20.86% vs 6.27%) and mixed (14.42% vs 4.31%) types, while E1 and E2 distributions were comparable for neutrophilic (2.51% vs 3.85%) and paucigranulocytic (3.25% vs 2.46%) types. E1 correlated with IL-5, fractional exhaled nitric oxide (FeNO), and blood eosinophils.

Posthoc analysis of E1 confirmed differences between neutrophilic and eosinophilic types (3.85% vs 20.86%; p = 0.024) and between paucigranulocytic and eosinophilic types (3.85% vs 20.86%; p = 0.020).

In their study, Curto and colleagues found that by employing flow cytometry, it was possible to identify two subsets of eosinophils in induced sputum in patients with persistent allergic asthma.

The authors also noted that some limitations of this study included its single-center nature and small number of patients, demonstrating the necessity for external validation to verify the results. Authors also indicated that the study findings provided new evidence on the possibility of identifying eosinophil subsets in induced sputum utilizing a noninvasive technique which launches opportunities for new areas of research in asthma and other respiratory diseases.

“Different eosinophil subsets can be identified in various organs and systems. For asthma, these subsets have already been identified in blood, but we have shown that they can also be identified in induced sputum”, researchers concluded, “The E1 subset (CD66b-high and CD15-high) predominates in patients with allergic asthma and eosinophilic inflammation and is correlated with blood eosinophils, FeNO, and IL-5 in sputum supernatant.”


—Yvette C. Terrie



Curto E, Mateus-Medina ÉF, Crespo-Lessmann A, et al. Identification of two eosinophil subsets in induced sputum from patients with allergic asthma according to CD15 and CD66b expression. Int J Environ Res Public Health. 2022;19(20):13400. doi:10.3390/ijerph192013400.