MECHANISMS OF HUMAN BASOPHIL & MAST CELL DESENSITIZATION

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Basophil and mast cell mediator release is a central feature of both acute and chronic allergic reactions. However, little is known of the biochemical nature of signal transduction in the human cells of this type. This proposal focuses on studies which will elucidate some of the important biochemical events in both IgE mediated and univalent hormone induced secretion. The primary goals of these studies is to elucidate the mechanisms of desensitization although significant effort will also be applied towards understanding activation events. In particular, the role of cytosolic calcium elevations and protein kinase C in activation and desensitization will be further examined. We have demonstrated that IgE-mediated histamine release in both human basophils and lung mast cells is accompanied by the increased activity of membrane associated protein kinase C and elevations in cytosolic calcium. Detailed studies suggest that desensitization processes are specific for the mediator being examined and that for regulating the extent of degranulation (histamine release), the basophil and mast cell regulate the activation of protein kinase C rather than elevations in cytosolic calcium. Therefore, part of this proposal seeks to understand in greater detail the relationship between PKC activation and histamine release, the multiple roles PKC may play in regulating mediator release and whether the transient activation in PKC activity results from the specific regulation of diacylglycerol levels. A series of exploratory experiments are proposed to determine whether tyrosine kinase activity plays a role in desensitization. Preliminary evidence also suggests that leukotriene release, unlike histamine release, is controlled by the down-regulation of the calcium response. The proposed studies will initially examine the relationship between down-regulation of the calcium response and down- regulation of leukotriene release. A second primary area of study will be on the relationship between calcium oscillations observed in single cells and subsequent mediator release. Several methods are proposed to measure single cell degranulation in an effort to correlate this end point with the early oscillatory changes in cytosolic calcium. In addition, the relationship between calcium oscillations and leukotriene release will be examined. A third aim of this proposal is to study the relationship between desensitization events that affect the early mediators (histamine and leukotrienes) and cytokine secretion which occurs much later in the secretory response. Since cytokine release appears dependent on mRNA accumulation, initial studies will focus on the mechanisms of mRNA accumulation.