The function and regulation of IL-33 in mast cell activation

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Background: IL-33, a member of the IL-1 cytokine family, is a crucial activator of mast cells. Full length IL-33 is a bioactive cytokine; however, mast cell proteases process this molecule by cleaving the central domain to release an IL-1-like cytokine domain, which increases its biological activity approximately 30-fold. The minimal IL-33 receptor complex is composed of the IL-1R4 (also known as ST2 or IL-33Ra) and the IL-1R3 (IL-1RAcP) chain. In mast cells the IL-33R complex is unique in that it associates with the receptor tyrosine kinase c-Kit. This conveys strong synergistic receptor crosstalk and adds a further level of complexity to IL-33-mediated responses. Recent evidence suggests that IL-33 activities are dependent on purinergic P2-receptor (P2R) activation. In mast cells, the ATP-P2R pathway has been shown to have a central activating and pro-inflammatory role, while inhibition of P2R expression on mast cells maintains tissue homeostasis. In addition, we have recently shown that adenosine signalling via the purinergic P1 receptor (A3) decreases IL-33R expression and inhibits the IL-33 provoked potentiation of IgE and antigen induced degranulation. This suggests a reciprocal and dynamic control of IL-33 activity in mast cells dependent on the production and metabolism of ATP and ADP. It is currently unknown if the IL-33/P1R- and P2R-induced human mast cell activation and consequent release of mediators is the result of receptor crosstalk let alone what the molecular mechanisms underlying this activity might be.Key aims: The aims of the project are: 1. To investigate the means by which human mast cells are activated by IL-33 alone and in synergism with the ATP/ADP pathways and to define the nature of the IL-33-induced secretome.2. To study both the effect of IL-33 on the pattern of mast cell P1 and P2 receptor expression and the reciprocal effect of ATP/ADP pathway on IL-33R expression and IL-33 protein processing and signalling in human mast cells.3. Investigate the consequences of human mast cell activation via IL-33, in synergy with ATP/ADP, on human innate lymphocyte (ILC) 2 behaviour.Potential outcomes: The study is likely to provide new understanding of the biological basis of IL-33 activities on human mast cells. Training: Methodologically, the project will include culturing and differentiation of human mast cells and other cell lines and the evaluation of their function by state-of-the-art flow cytometry, advanced immunofluorescence, transcriptomic analysis, deep immunophenotyping and metabolic/proteomic approaches.