Association of type 2 cytokines in severe rhinovirus bronchiolitis during infancy with risk of developing asthma: A multicenter prospective study

Abstract

To the Editor, Bronchiolitis is the leading cause of hospitalizations in U.S. infants. In addition to the acute morbidity, cohort studies have also shown that 30%‐40% of infants hospitalized for bronchiolitis (severe bronchiolitis) develop childhood asthma. Particularly, early life infection with rhinovirus (RV)—the second most common pathogen of bronchiolitis—is associated with an increased risk of childhood asthma. Yet, the mechanism through which RV raises asthma risk in infants is largely unknown. Experimental models and human (cross‐sectional and retrospective) studies have reported that RV infection may induce type 2 cytokines (eg, interleukin [IL]‐4, IL‐5, IL‐13, thymic stromal lymphopoietin [TSLP]) and that the levels of these cytokines are elevated in the asthmatic airway. However, no prospective study has investigated the longitudinal relation of type 2 airway inflammation in children—let alone infants with bronchiolitis—to the development of childhood asthma. To address this knowledge gap, we prospectively examined the association of nasopharyngeal cytokines in infants with RV bronchiolitis with the risk of developing childhood asthma, by using data from a multicenter cohort of infants with severe bronchiolitis. Details of the study design, samples, measurement, and analysis may be found in the Methods S1). Briefly, this multicenter prospective cohort study, the 35th Multicenter Airway Research Collaboration (MARC‐35), enrolled 1016 infants (aged < 12 months) hospitalized for bronchiolitis at 17 sites across 14 US states (Table S1) during the 2011‐2014 winter seasons. Bronchiolitis was defined by the American Academy of Pediatrics guidelines. In addition to the phenotypic data measurement via structured interview and medical record review, nasopharyngeal airway samples were collected within 24 hours of hospitalization using a standardized protocol. Levels of 10 nasopharyngeal cytokines (IL‐4, IL‐5, IL‐10, IL‐12, IL‐13, IL‐25, IL‐33, interferon [IFN]‐β, macrophage inflammatory protein [MIP]‐1α, and TSLP) were quantified using electrochemiluminescence immunoassays. Respiratory viruses were tested using real‐time PCR assays for RV and respiratory syncytial virus (RSV). To quantify the relative RV genomic load, cycle threshold (CT) values—the number of amplification cycles needed for a positive PCR test result—were used. The primary outcome was asthma at age 4 years based on a commonly used epidemiologic definition—that is, physician diagnosis of asthma plus either asthma medication use or asthma‐related symptoms in the past year. For the current study, we analyzed 132 infants with RV bronchiolitis who underwent nasopharyngeal cytokine measurement. To examine the association of exposures (cytokine levels and RV genomic load) with asthma, we used generalized linear mixed‐effects models, adjusting for potential confounders (age, sex, parental history of asthma, breathing problems prior to enrollment, IgE sensitization [aeroallergens or food], and virology [solo RV, RV/RSV coinfection]) and hospital‐level clustering. As the models indicated statistically significant virology‐exposure interactions, we then stratified the analysis by virology. Of 132 infants with severe RV bronchiolitis, the median age was 4 (IQR 2‐6) months, 64% were male, 40% were non‐Hispanic white, and 55% had RSV coinfection. Asthma was observed in 30% of children at age 4 years (Tables 1 and S2). There were statistically significant interactions between virology and six cytokine levels (IL‐4, IL‐5, IL‐13, IFN‐β, MIP‐1α, and TSLP) on the asthma risk (Pinteraction < 0.05), indicating that exposure‐asthma associations differ between solo RV infection and RV/RSV coinfection. Indeed, in infants with solo RV infection, the cytokine levels (IL‐4, IL‐5, and TSLP) and RV genomic load significantly differed between those with and without asthma (unadjusted P < 0.05; Table S3) while there were no differences in those with RV/RSV (unadjusted P > 0.05). Heatmap (Figure S1) also showed that distributions of these type 2 cytokines differed by virology and outcome. In the adjusted analysis (Figures 1 and S2), only infants with solo RV bronchiolitis had significant associations of higher type 2 cytokine levels (IL‐4, IL‐5, IL‐13, and TSLP) with an increased risk of asthma (adjusted P < 0.05). In the sensitivity analysis using normalized cytokine levels and the subgroup analysis excluding infants with a breathing problem prior to enrollment, the results were similar (Figures S3 and S4). These findings are concordant with previous cross‐sectional and retrospective studies that suggested potential interrelations between RV infection, type 2 cytokines (eg, IL‐4, IL‐5, IL‐13, TSLP), and asthmatic airway inflammation. The current prospective study builds on these earlier reports and extends them by demonstrating the prospective association between type 2 cytokine levels in the airway of infants with solo RV bronchiolitis and the risk of developing asthma. The mechanisms underlying these findings warrant further investigation. It is possible that severe RV infection is an early marker of TH2 bias in predisposed infants, which leads to augmented RV infection and replication. Yet, our data also showed no significant correlations between serum total IgE levels and nasopharyngeal cytokine levels (Table S4). Alternatively, the association may be DOI: 10.1111/all.13723