Exploring the clinical, functional and biological heterogeneity of a monocentric cohort of asthmatic patients with neutrophilic inflammation: a “bioptic” approach

BACKGROUND. T2LOW phenotypes of asthma are poorly characterized with an important lack of validated clinical biomarkers for clinical routine and a scarce therapeutic offer. The challenge is represented by the high heterogeneity of the disease, due to genetics, and host and environmental factors. The analysis of the inflammatory processes behind this condition and, in particular, the characterization of cells and mediators of the bronchial submucosa is a fundamental step. In this context the “inflammometric” evaluation of patients’ bronchial biopsies offers a privileged approach for a direct investigation of the cellular, structural and molecular profile of the lung tissue, combined with clinical manifestation and functional characteristics. AIM. This PhD thesis – a large cross-sectional observational study on bronchial biopsies collected from moderate-to-severe asthmatic patients - aimed to shed a light on asthma phenotypes with neutrophilic inflammation to decode its complexity and heterogeneity, defining the clinical and functional characteristics and connecting them with specific bronchial inflammatory patterns and molecular signatures. Stratification was made according to (I) (the absence of) clinical T2 biomarkers; (II) the degree of bronchial neutrophilia, to evaluate characteristics of neutrophilic inflammation per se, or (III) severity and CS resistance to search for a link with bronchial neutrophils as well as significant comorbidities. METHODS. Bronchial biopsies obtained from mild-to-severe asthma patients, were collected and analysed through immunohistochemistry or immunofluorescence. Still, the clinical data were also analysed and interpolated with molecular data, in the view to obtain functional information. RESULTS. Neutrophilic inflammation is associated with higher disease severity and a poor response to the standard therapies. It could be – or not – associated with allergic sensitization and IgE-mediated responses. Bronchial neutrophilia differentially involves the activation of T1 and T17 immunity, NLRP3 inflammasome, molecules associated with neutrophilic function such as IL-8, RANTES and CCR-5, and the alarmin TSLP. Each mechanism seems to be associated with different magnitudes of bronchial neutrophilia, different degrees of severity or specific remodelling phenomena (vascular remodelling), influenced by comorbidities, and specific host and environmental factors. Undoubtedly, the overlap of multiple mechanisms – either innate or acquired - is responsible for the poorest outcomes. This is more often observed in those subjects with longest asthma duration, suggesting that the prolonged interplay between host and environmental factors are pivotal in determining the natural history of asthma. The proper pheno- and endo-typization of asthma with neutrophilic inflammation will be pivotal in future research. These data also suggest pulmonologists to consider investigative bronchoscopy in those cases of severe or difficult-to-treat forms of asthma.