IL-17 drives the recruitment of b cells to the bronchial tissue of severe asthmatic patients

Background: B-cells play an important role in asthma development mostly via the production of IgE. A number of reports have shown local production of IgE in B cells present in lung tissues of mild allergic asthmatics. However, it is not clear whether there is an increase in the number of B cells in severe asthma and how do B cell migrates to the mucosal site. Our objective in this study was to determine the number and pattern of infiltrated B cells into lung tissues in severe compared to mild asthma and to investigate the mechanism behind this infiltration. Methods: Bronchial biopsies from severe versus mild asthmatics were stained for B cells marker (CD20) using Immunohistochemistry. Moreover, migration towards IL-17 gradient was determined using Boyden chamber. Results: The number of CD20 positive cells in severe asthmatic biopsies was significantly higher than those in mild asthmatics. Interestingly, we have also observed lymph follicles in 40% of severe compared to 15% of mild asthmatic airways. Most of the cells in the lymph follicles were CD20 positive cells. These lymph follicles were very close to the epithelial surface. We have recently reported high expression of IL-17 in severe asthma. We tested the hypothesis that IL-17 is involved in migration of B cells to the mucosal surface of the airways. Although B cells were shown to migrate towards both IL-17A and IL-17F, much lower concentrations of IL-17F, compared to IL-17A, were sufficient to induce migration. Moreover, B cells within airway mucosa of severe asthmatics were shown to express higher level of IL-17R compared to those of mild asthmatic patients using immunohistochemistry as well as qPCR. Conclusion:IL-17 might drive the migration of B cells in the lung tissues and could play a critical role in the formation of lymphoid follicles in severe asthmatic airways.