Immunophenotype of airway eosinophils in severe eosinophilic asthma

<bold>Background:</bold> In severe asthma, airway inflammation persists despite high doses of inhaled corticosteroids and shows variable response to biologics, which may suggest specificities in the biology of airway eosinophils (Eos). This study investigated the expression of surface proteins by airway Eos in severe asthma. <bold>Method:</bold> We included patients with uncontrolled severe asthma (ACQ-6≥1.5) free from systemic corticosteroids and biologic. Blood and induced sputum were incubated with the antibodies of interest and analysed by flow cytometry (CD45, CD16, CD63, CD193, CRTH2, CD125, CD44, CD69, HLA-DR, CD123, CD62, 7AAD, Siglec-8). Unsorted Eos were identified using a CD45+/CD16- and 7AAD-/CD45+/Siglec-8+/CD16- gating in blood and sputum, respectively. Median fluorescence intensity was compared between airway and blood Eos using a Wilcoxon test. <bold>Results:</bold> Among 24 participants, 9 were analysed (women 78%, age 53 years (48-58), blood Eos: 374/mm3 (342-501)). All met the definition of eosinophilic asthma (blood Eos≥300/mm3 and/or airway Eos≥3%). In comparison with blood, airway Eos showed an activation state with increased expression of CD69 (p<0.01) but no modulation of CD63 and (p=0.3) or HLA-DR (p=0.55). They showed a specific immunophenotype characterized by decreased expression of Siglec-8 (p<0.01), CRTH2 (p=0.02), CCR3 (p=0.02), CD44 (p=0.02), and CD123 (p<0.01) and abolition of CD62L (p<0.01) and CD125 (p=0.02). <bold>Conclusion:</bold> In severe eosinophilic asthma, airway Eos are activated and have a specific immunophenotype. These results provide information on targets present on airway Eos in view of inhaled drug development.