Increased nasal plasmacytoid dendritic cells are associated with recurrent wheezing following severe respiratory syncytial virus bronchiolitis in infancy.

To the Editor: Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract illnesses in young children.1 The pathogenesis of subsequent asthma and reduced lung function following severe RSV bronchiolitis remain unclear. As only a fraction of these children develop recurrent wheezing and asthma, the variation in host factors and immune response are thought to be important in determining these outcomes.2 Pulmonary dendritic cells (DCs) modulate Tcell responses and limit airway inflammation in RSVinfected mice3,4; and differences in DC subsets exist between young children hospitalized with RSV and healthy controls5 leading us to hypothesize that children who develop recurrent wheeze following RSV bronchiolitis have a discrepancy in the frequency of peripheral and/or nasal DCs, compared with children who do not wheeze following severe RSV bronchiolitis in infancy. In this study, nasal wash and blood samples were collected from infants <1 year of age while hospitalized with their first episode of RSVconfirmed bronchiolitis enrolled in the RSV Bronchiolitis in Early Life 2 (RBEL2) study from 2009 to 2012.2 Nasal wash samples were collected from patients by nasal suctioning, in accordance with a validated protocol.6 We excluded children with history of previous wheezing, asthma, congenital heart, and lung anomalies, cystic fibrosis, and history of regular use of reflux medications, bronchodilators, and antiinflammatory medications. Informed consent was obtained from the parents/guardian of all patients at enrollment, and the study was approved by the Institutional Review Board at Washington University. Of 209 children in the cohort, 194 children had nasal and/ or blood samples at entry. Adequate nasal washes were obtained from 122 (58%) and blood samples were obtained from 178 (85%) children. The mean duration of bronchiolitis symptoms to blood collection was 1.7 ± 1.1 days. The mean duration of bronchiolitis symptoms to nasal sample collection was 0.9 ± 0.4 days. The methods for the assessment of nasal DCs, and blood DCs were previously published.7,8 (detailed methods are provided in this article's Online Repository). Plasmacytoid DCs (pDC) were identified as Lin− (CD3, CD19,CD14, CD20, CD16, CD56), CD123 +, HLADR+, and myeloid DCs (mDC) were identified as Lin− CD11c+ HLADR+. Type −1 myeloid DCs (mDC1) were identified by CD1c, and type −2 myeloid DCs (mDC2s) were identified by CD141 (BCDA3) expression. The wheezing outcomes were obtained during telephone interviews with parents/guardians every 6 months. Wheezing was defined as a positive response to either “Has your child had wheezing with colds?” or “Has your child had wheezing without colds?”. Recurrent wheezing was defined as three or more wheezing episodes. Ttests, chisquare tests, and Fisher's exact tests were used to test for clinical variable differences between the wheezing groups (recurrent vs no wheezing). Age at most recent followup and all variables which differed between the groups at p < .10 were entered into multivariable logistic regression models to obtain modeladjusted odds ratios (OR) for nasal and blood DCs on the outcome of recurrent wheezing. Longitudinal followup data were available for 182 of the 194 children with nasal and/or blood samples. Of these, the mean age ± SD at enrollment was 4.3 ± 3.0 months, 42% were African– Americans, and 47% were Caucasians. The mean age at last followup was 4.2 ± 1.9 years and the mean duration of followup was 46.3 ± 23.3 months (range 0.6– 99.4 months). Of 122 children with nasal samples, 117 (96%) had longitudinal followup. Of those with longitudinal followup, 55 (47%) had recurrent wheezing and 25 (21%) had no wheezing. Similar wheezing outcomes were observed in 178 children with blood samples, of which 167 (94%) had longitudinal followup (42% had recurrent wheezing and 26% had no wheezing). We did not find differences in most baseline demographics including age at entry, age at most recent followup, gender, race, family history of atopy/asthma, and exposure history (daycare attendance, intrauterine/postnatal smoke exposure) between children who had samples obtained for blood/nasal DCs and children without samples (Table S2). Recurrent wheezers had a higher proportion of African– Americans and longer duration of followup than children with no subsequent wheeze (Table S1). Compared to children with no wheezing, the recurrent wheezers had significantly higher frequency of Plasmacytoid DCs (pDCs) in nasal washes than children who never wheezed (1.7 ± 2.2 vs 0.8 ± 1.7%, p = .003), Table 1 and Figure 1. The frequency of blood