The long term goal of this project is to understand the mechanisms of natural killer (NK) cell activation and their role in human diseases. NK cells are innate immune effector cells named for their ability to kill tumor cells. Subpopulations of NK cells also release the cytokine, IL-5, thereby modulating the immune response to allergens. However, there are fundamental questions that remain to be addressed. Do NK cells directly respond to allergens? What is the mechanism for this direct recognition? Here we propose to determine the mechanism for NK cell responses to a subset of inflammatory signals, namely proteases from self or allergen sources. Our preliminary data suggests NK cells express protease activated receptor (PAR-1), and this receptor activates NK cells. Furthermore, PAR-1 recognition of Alternaria fungus-derived proteases alters NK cell activation. In this proposal, we will characterize the mechanism of NK cell stimulation via the PAR-1 receptor. We hypothesize: 1) PAR-1 modulates NK cell activation, and 2) Alternaria directly alters NK cell activation through PAR-1 recognition of Alternaria-derived proteases. To test these hypotheses, we propose these specific aims: Aim 1.) Characterize the downstream signals of activated PAR-1 in NK cells; Aim 2.) Determine the functional outcome of PAR-1 stimulation in NK cells; Aim 3.) Characterize the direct interaction between Alternaria proteases and NK cells via PAR-1. We will use several methods to achieve these aims, including PAR-1 specific stimulation, PAR-1 suppression, calcium signaling assays, cytokine release functional assays, cytotoxicity functional assays, and Alternaria stimulation of NK cells. Upon completion of these aims, we will demonstrate the mechanism by which NK cells respond to fungal allergen Alternaria, produce IL-5, and thus mediate the allergic response. These studies will allow us to characterize a unique mechanism for NK cell activation under inflammatory conditions. Relevance: This project will help elucidate a unique mechanism for NK cell activation. This information is useful for developing novel therapeutic targets, such as PAR inhibitors, to alleviate allergic diseases. [unreadable] [unreadable] [unreadable]