Circulating IL-6 associates with a distinct pediatric asthma subtype and serves as a potential key predictor for risk...

Childhood asthma is a heterogeneous disease wherein systemic inflammation, particularly involving nontype 2 cytokines such as interleukin-6 (IL-6), is not universally present and its clinical significance remains unclear. This cross-sectional observational study aimed to elucidate the association between circulating IL-6 levels and the phenotypic characteristics of pediatric asthma, and to explore the potential value of IL-6 as a predictive biomarker for asthma phenotypic risk stratification.

Plasma IL-6 levels were quantified in 105 newly diagnosed pediatric asthma patients (≤15 years old) and 104 age-matched healthy controls to establish a normal reference range. Asthma patients were stratified into two subgroups based on a predefined threshold: "IL-6-normal" (<3.1 pg/mL) and "IL-6-high" (≥3.1 pg/mL, the 95th percentile of IL-6 levels in the healthy control group). Clinical, inflammatory, and lung function characteristics were compared between the two subgroups. Spearman's rank correlation analysis was conducted to explore the associations between cytokine levels and lung function/airway inflammation indices. Multivariate logistic regression analysis was performed to identify variables associated with asthma phenotypic characteristics, and subsequent feature selection was carried out using Least Absolute Shrinkage and Selection Operator (LASSO) regression with fivefold cross-validation. A priori sample size estimation and sex-stratified analyses were conducted, and all methods followed STROBE reporting guidelines.

Compared with healthy controls, pediatric asthma patients had significantly elevated serum IgE levels, peripheral blood eosinophil counts, and plasma concentrations of IL-4, IL-6, and IL-12 (all p < 0.05). Among the asthma cohort, the "IL-6-high" subgroup (n = 20, 19.0%) had significantly higher body mass index (BMI) and plasma IL-12 levels relative to the "IL-6-normal" subgroup (n = 85). Sex-stratified analyses demonstrated consistent patterns of elevated IL-6-related airway inflammation and reduced lung function across male and female children, without significant subgroup divergence. Correlation analysis showed that plasma IL-4 levels were significantly negatively correlated with percent predicted forced expiratory volume in 1 s (FEV₁; r = -0.245, p = 0.025), and plasma IL-6 levels were significantly positively correlated with fractional exhaled nitric oxide (FeNO) levels (r = 0.214, p = 0.021). Multivariate logistic regression analysis identified asthma onset after 4 years of age, oral corticosteroid use, blood eosinophil count, FeNO level, and percent predicted FEV₁ as variables independently associated with asthma phenotypic characteristics. Notably, LASSO regression selected circulating IL-6 as the most prominent predictive biomarker for asthma phenotypic characteristics among all evaluated clinical, inflammatory, and lung function variables. A predictive nomogram incorporating key variables showed excellent discriminative performance in the training cohort (C-index = 0.85, 95%CI: 0.79-0.91) and was validated in an independent cohort (C-index = 0.82, 95%CI: 0.75-0.89).

Elevated circulating IL-6 is a prominent feature associated with a distinct phenotypic subgroup of pediatric asthma, and is correlated with impaired lung function and increased airway inflammation in asthmatic children. These findings support the potential of IL-6 as a significant predictive biomarker for phenotypic risk stratification in pediatric asthma, and suggest its potential utility in phenotypic subtyping of asthmatic patients and as a promising therapeutic target for the IL-6-high pediatric asthma subgroup. All conclusions are interpreted cautiously, given the study's methodological limitations, and further large-cohort prospective validation is required.