IL-33 fine-tunes mast cell degranulation and chemokine production at the single cell level

Abstract Background Mast cells are versatile key components of allergy and inflammation, known to respond to both innate and adaptive immunological stimuli. However the response of individual mast cells to cumulative stimuli remains poorly understood. Objectives To dissect mast cell responses at the single-cell level and their potentiation by IL-33. Methods We monitored mast cell degranulation in real time by exploiting the capacity of fluorochrome-labeled avidin to stain degranulating cells. During the degranulation process, granule matrix is externalized and immediately bound by fluorochrome-labeled avidin present in the culture medium. The degranulation process is monitored either by time-lapse microscopy or FACS analysis. Results Single cell analysis revealed a strong heterogeneity of individual mast cell degranulation responses. We observed that the number of degranulating mast cells was graded according to the FcεRI stimulation strength whereas the magnitude of individual mast cell degranulation remained unchanged, suggesting an all-or-none response of mast cell following FcεRI triggering. IL-33 pretreatment increased not only the number of degranulating and chemokine producing mast cells but also the magnitude of individual mast cell degranulation and chemokine production. Conclusion We illustrate the impact of IL-33 on mast cell biology at the single cell level by showing that IL-33 potentiates IgE-mediated mast cell responses by both increasing the number of responding cells and by enhancing the responses of individual mast cells.