Infants diagnosed with bronchiolitis and hospitalized at the Department of Respiratory Disease at Children’s Hospital Soochow University, China, from November 2016 through March 2017, were enrolled in this study. Nasopharyngeal aspirates were obtained for detecting respiratory virus and analyzed by reverse-transcriptase polymerase chain reaction (RT-PCR) and direct immunofluorescent assay. Serum cytokines including TSLP, IL2, IL13, TIMP-1, MMP-9, IL33, IL5, IL4, IL25, TNF- α and MIP-1α were measured by flow cytometry. The patients were followed every 3 months for a duration of 2 years by telephone or at outpatient appointments.
Recurrent wheezing was defined as two or more episodes following initial bronchiolitis for two years. The study was approved by the ethics committee of the Children’s Hospital Soochow University (Approval No.:2016050). Informed consent was obtained from the parents of all children enrolled in this study.
Inclusion criteria: 1) Age: 1–24 months; 2) Patients were hospitalized with bronchiolitis; 3) Bronchiolitis was defined as the first wheezing episode characterized by cough, tachypnea and chest retractions.
Exclusion criteria: Neuromuscular disease, congenital airway deformity, congenital heart disease, gastroesophageal reflux disease, bronchial foreign body inhalation, primary or secondary immune deficiency or other immune-associated diseases were excluded.
Disease severity criteria: according to Wang expiratory flow limitation (EFL) scoring[18], the severity of disease was graded as follows (Table 1): 0–4.9 was mild; 5–8.9 was moderate; 9–12 was severe.
Sample collection
Nasopharyngeal aspirates were obtained using a suction catheter passed through the nose into the lower part of the pharynx for detection of viruses. Peripheral venous blood (2 ml) was also collected for detection of blood routine, humoral and cellular immunity and cytokines.
Detection of seven common viruses by direct immunofluorescent assay (DFA)
DFA was used to detect respiratory syncytial virus (RSV), influenza virus A (IVA), influenza virus B (IVB), parainfluenza virus (PIV) I, PIV II, PIV III, and adenovirus (ADV). All assay kits were purchased from Chemicon (USA) and all staining procedures were performed according to the manufacturer’s instructions. Immunostained preparations were viewed with a fluorescence microscope (Leica 020-518.500, Germany).
Detection of the metapneumovirus (hMPV), rhinovirus (hRV), bocavirus (hBoV) gene by real-time polymerase chain reaction (RT-PCR)
For hMPV detection, primers were designed to specifically amplify the N gene (213 base pairs [bps]). The forward and reverse primers were hMPV-F:5’- AACCGTGTACTAAGTGATGCACTC-3’ and hMPV-R:5’- CATTGTTTGACCGGCCCCATAA-3’, respectively. The cyclic temperature settings were 94 °C, 30 s; 55 °C, 30 s; 68 °C, 30 s; amplified by 45 cycles with the last at 68 °C for 7 min.
For hRV detection, the primers and probe sequences were HRV-F: 5’-TGGACAGGGTGTGAAGAGC-3′;HRV-R:5’-CAAAGTAGTCGGTCCCATCC-3′;HRV-probe:FAM-TCCTCCGGCCCCTGA ATG-TAMRA. The cyclic temperature settings were 94℃, 30 s; 56℃, 30 s; 72℃, 30 s; amplified, 40 cycles.
For hBoV detection, the primers and probe sequences were HBoV-F:5’-TGACATTCAACTACCAACAACCTG-3’;HBoV-R:5’CAGATCCTTTTCCTCCTCCAATAC-3′; HBoV-probe: FAMAGCACCACAAAACACCTCAGGGG-TAMRA. The cyclic temperature settings were 94℃,30 s; 56℃, 30 s; 72℃, 30 s; amplified for 40 cycles.
Routine blood test
Peripheral venous blood (2 ml) was collected and anticoagulated with EDTA from every patient. The blood was tested by an automatic five classification hematology analyzer for white blood cell count, absolute neutrophil count, absolute lymphocyte count and absolute count of eosinophils.
Testing of humoral immunity
Detection indices: IgG, IgM and IgA. IgG and IgM were determined by transmission immunoassay, and IgA was determined by immunoturbidimetry.
Testing of cellular immunity
Peripheral venous blood (2 ml) was collected on EDTA anticoagulant. Flow cytometry of Beckman Coulter company was used for analysis. The kit was purchased from Immunotech (France). Detection indices: CD3+, CD3+ CD4+, CD4+ / CD8+, CD3+CD8+, CD19+CD23+, CD3-CD16+CD56+ and CD3-CD19+.
Detection of serum levels of cytokine
The peripheral blood was centrifuged at 2500r/min for 5 minutes. Supernatants were frozen at -80℃. Serum levels of cytokines (TNF-a, IL-2, IL-13, IL-4, IL-5, IL-25, IL-33, TSLP, TIMP-1, MMP-9 and MIP-1α) were measured by flow cytometry. Flow cytometry (Beckman Coulter, Brea, CA, USA) was performed according to the manufacturer's instructions (Immunotech, Marseille, France). All assay kits were purchased from BEIJING TONGSHENG SHIDAI BIOTECH CO., LTD. Data were automatically processed and analyzed using FCAP Array 3.0 with the standard curve produced from the cytokine standard.
Data collection
Each patient’s data, including age, gender, gestational age at delivery, birth weight, feeding patterns, history of eczema, family history of asthma, exposure to smoking, and pet contact were recorded.
Follow-up of patients
After discharge from hospital, the patients were followed up every 3 months for a 2‑year period by outpatient visits or telephone consultations.
Statistical analysis
SPSS version 18.0 software was used for data analysis. Distribution normality of continuous data was tested by the P-P plots methods before comparison. Data with normal distribution were represented as mean ± standard deviation (SD) and analyzed by t tests. Continuous data with non-normal distribution were represented as median (minimum-maximum) and analyzed with the Mann-Whitney U test. Categorical data were represented as frequency and analyzed with Chi square examination. Predictors of recurrent wheezing were analyzed using a stepwise logistic regression model.