Upper Airway Alarmin Cytokine Expression in Asthma of Different Severities

Background: The secretion of alarmin cytokines by epithelial cells, including thymic stromal lymphopoietin (TSLP), interleukin (IL)-25, and IL-33, heralds the onset of the inflammatory cascade and immune effector infiltration in asthma. However, alarmin cytokine expression in the upper airways in asthma remains largely unknown. Methods: We recruited 40 participants with asthma who were categorized into four severity groups as per the Global Initiative for Asthma (GINA) classifications (10 in each group of GINA-1/2, -3, -4, and -5). Cells were derived from buccal, nasal and throat brushings, and intracellular alarmin cytokine expression (TSLP, IL-25, and IL-33) was assessed in cytokeratin 8+ (Ck8+) epithelial cells immediately after collection using flow cytometry with fluorescence minus one (FMO) controls. We assessed differences in alarmin cytokine expressions across asthma severity using quantile regression adjusted for age and sex. Results: Of all patients, 24 (60%) were females with a mean (standard deviation [SD]) age of 41 (16) years. TSLP levels in Ck8+ epithelial cells in nasal samples of GINA-5 patients were significantly (p=0.03) higher than other GINA groups after adjusting for age and sex but did not differ between patients with and without nasal comorbidities. However, we did not find any significant changes in TSLP levels in Ck8+ epithelial cells in buccal and throat samples across GINA groups. IL-25 or IL-33 (obtained from nasal, buccal, and throat epithelial cell samples) were not significantly different across GINA groups. Conclusions: Our study demonstrates for the first time that Ck8+ nasal epithelial cells from GINA-5 asthmatics express elevated levels of TSLP.