Chronic airway inflammation provides a unique environment for B cell activation and antibody production.

BACKGROUND: B cells play many roles in health and disease. However, little is known about the mechanisms that drive B cell responses in the airways, especially in humans. Chronic rhinosinusitis (CRS) is an inflammatory disease of the upper airways that affects 10% of Europeans and Americans. A subset of CRS patients develop nasal polyps (NPs), which are characterized by type 2 inflammation, eosinophils and group 2 innate lymphoid cells (ILC2s). We have reported that NP contain elevated levels of B cells and antibodies, making NP an ideal system for studying B cells in the airways. OBJECTIVE: We sought to determine the mechanisms that drive B cell activation and antibody production during chronic airway inflammation. METHODS: We analysed B cells from NP or tonsil, or after ILC2 coculture, by flow cytometry. Antibody production from tissue was measured using Luminex assays and the frequency of antibody-secreting cells by ELISpot. Formation of B cell clusters was assessed using immunohistochemistry. Expression of genes associated with B cell activation and class switch recombination was measured by qRT-PCR. RESULTS: NP contained significantly elevated frequencies of plasmablasts, especially those that expressed the extrafollicular marker Epstein-Barr virus-induced protein 2 (EBI2), but significantly fewer germinal centre (GC) B cells compared with tonsil. Antibody production and the frequency of antibody-secreting cells were significantly elevated in NP, and there was evidence for local class switch recombination in NP. Finally, ILC2s directly induced EBI2 expression on B cells in vitro. CONCLUSIONS AND CLINICAL RELEVANCE: Our data suggest there is a unique B cell activation environment within NP that is distinct from classic GC-mediated mechanisms. We show for the first time that ILC2s directly induce EBI2 expression on B cells, indicating that ILC2s may play an important role in B cell responses. B cell-targeted therapies may provide new treatment options for CRSwNP.

Pathogenesis of nasal polyposis.

Chronic rhinosinusitis with nasal polyps (CRSwNP) is a complex inflammatory condition that affects a large proportion of the population world-wide and is associated with high cost of management and significant morbidity. Yet, there is a lack of population-based epidemiologic studies using current definitions of CRSwNP, and the mechanisms that drive pathogenesis in this disease remain unclear. In this review, we summarize the current evidence for the plethora of factors that likely contribute to CRSwNP pathogenesis. Defects in the innate function of the airway epithelial barrier, including diminished expression of antimicrobial products and loss of barrier integrity, combined with colonization by fungi and bacteria likely play a critical role in the development of chronic inflammation in CRSwNP. This chronic inflammation is characterized by elevated expression of many key inflammatory cytokines and chemokines, including IL-5, thymic stromal lymphopoietin and CCL11, that help to initiate and perpetuate this chronic inflammatory response. Together, these factors likely combine to drive the influx of a variety of immune cells, including eosinophils, mast cells, group 2 innate lymphoid cells and lymphocytes, which participate in the chronic inflammatory response within the nasal polyps. Importantly, however, future studies are needed to demonstrate the necessity and sufficiency of these potential drivers of disease in CRSwNP. In addition to the development of new tools and models to aid mechanistic studies, the field of CRSwNP research also needs the type of robust epidemiologic data that has served the asthma community so well. Given the high prevalence, costs and morbidity, there is a great need for continued research into CRS that could facilitate the development of novel therapeutic strategies to improve treatment for patients who suffer from this disease.