The role of B cell Activating Factor (BAFF) expression on pathogenesis of nasal polyp in chronic rhinosinusitis with nasal polyposis.

Background: B cells, plasma cells, and local immunoglobulins, are important as a mucosal immune barrier function, and tend to increase in patients with chronic rhinosinusitis with nasal polyposis (CRSwNP). However, their association with eosinophils' aggregation has not been fully understood. The objectives of this study was to explore whether BAFF expression in the subepithelial area in nasal polyp tissues of CRSwNP was associated with eosinophils' accumulation, and also to evaluate cells which cells produce BAFF.

Methodology: Immunohistochemical and immunofluorescence staining were used to analyse expression of BAFF, CD20, immunoglobulin A (IgA) and a proliferation inducing ligand (APRIL) on nasal tissues from CRSwNP patients to control subjects. To identify the relationship between BAFF and tissue eosinophilia, CRSwNP subjects were divided into eosinophilic polyp and non-eosinophilic groups. Double immunofluorescence analysis for BAFF and CD11c or CD11b was performed to identify cells producing BAFF.

Results: The numbers of BAFF, CD20, and IgA-positive cells in the subepithelial area were significantly higher in the CRSwNP group (both eosinophilic polyps and non-eosinophilic polyps. There were statistically significant correlations between the number of BAFF and CD20-positive cells, CD20 and IgA-positive cells, and BAFF and IgA-positive cells. CD11b-positive were co-localized with BAFF positive cells.

Conclusion: The subepithelial expression of BAFF was associated with increased number of B cells and plasma cells, and increased production of IgA in the patients with CRSwNP, especially eosinophilic nasal polyps. Therefore, BAFF-induced IgA production may be associated with eosinophils' aggregation and degranulation, which cause aggravation of tissue inflammation and finally polyp formation. The expression of BAFF in the subepithelial area may be associated with innate inflammatory cells (CD11b+ cells), such as monocytes, granulocytes, macrophages, and natural killer cells.