Circulating Interleukin-11 Across Allergic and Non-Allergic Airway Disease Phenotypes: A Single-Center Exploratory Study.

Interleukin-11 (IL-11) is implicated in epithelial dysfunction, fibroblast activation, tissue remodeling, and chronic inflammatory responses; however, the clinical value of circulating IL-11 in airway disease remains uncertain. This single-center retrospective exploratory observational study included 88 adults: 31 with allergic rhinitis, 15 with non-allergic asthma, 22 with allergic asthma associated with allergic rhinitis, and 20 healthy controls. Serum IL-11 concentrations were measured using a quantitative sandwich enzyme-linked immunosorbent assay. Between-group differences were assessed using the Kruskal-Wallis test followed by Holm-adjusted pairwise Mann-Whitney U tests. Associations with disease-specific ordinal clinical categories were evaluated using Spearman rank correlation, with GINA treatment Steps used for asthma phenotypes and ARIA severity categories for allergic rhinitis. Median IL-11 concentrations were 62.01 pg/mL in non-allergic asthma, 78.87 pg/mL in allergic rhinitis, 61.92 pg/mL in allergic asthma associated with allergic rhinitis, and 95.46 pg/mL in healthy controls. The primary global comparison was not statistically significant (H = 5.667, p = 0.129), and no pairwise comparison remained significant after Holm correction. Six measurements (6.8%) were below the assay detection limit; replacing these values with 4.0 pg/mL in a sensitivity analysis did not materially alter the global result (H = 5.671, p = 0.129). Serum IL-11 was not significantly associated with GINA treatment step in non-allergic asthma (rho = -0.170, p = 0.544) or allergic asthma associated with allergic rhinitis (rho = 0.052, p = 0.818), nor with ARIA severity category in allergic rhinitis (rho = 0.046, p = 0.805). In an exploratory analysis adjusted for age, sex, body-mass category, and current smoking status, IL-11 concentrations were lower in each clinical phenotype relative to healthy controls; given the modest group sizes and baseline imbalance, this finding was considered hypothesis-generating. Overall, the primary analysis did not demonstrate significant differences in circulating IL-11 across study groups, and serum IL-11 was not associated with disease-specific ordinal clinical categories. These findings do not support the use of a single serum IL-11 measurement as a stand-alone biomarker of airway disease phenotype or clinical category in this cohort and warrant confirmation in larger, prospectively characterized cohorts.