Impact of Immune-Inflammatory Microenvironment Alterations on the Bronchial Lumen of Children With Protracted Bacterial Bronchitis

Protracted bacterial bronchitis is a syndrome that is among the most common causes of chronic cough. In order to understand its pathogenetic mechanisms, there is an increasing interest in the study of the immune microenvironment in the bronchial lumen. The aim of this retrospective study is the determination of the types and quantity of the inflammatory cells that infiltrate the bronchial epithelium as well as of the thickness of the basement membrane. Ninety-seven endobronchial biopsies, obtained from 77 children (30 males and 47 females) aged between 5 and 14 years, with chronic (>8 weeks) wet/productive cough, were subjected to hematoxylin and eosin staining. Using an appropriate image analysis and processing software, we determined the types and the quantity of the inflammatory cells that infiltrated the bronchial epithelium, and the thickness of the basement membrane. The metric data were then subjected to extensive statistical analysis. According to our results, females had increased levels of eosinophils (p = 0.021) and lymphocytes (p = 0.044) compared to males. Moreover, we found that membrane thickness was negatively correlated with the number of eosinophils (p < 0.0001), neutrophils (p = 0.023), and lymphocytes (p = 0.024). Finally, the pairwise comparisons of the number of eosinophils, neutrophils, lymphocytes, and other cell types revealed significant (p < 0.05) positive correlations. Protracted bacterial bronchitis activates pulmonary innate immune pathways. Also, it is accompanied by basement membrane thickening, which is a typical characteristic of several respiratory diseases, such as asthma.