The purpose of these studies is to elucidate the mechanisms of human basophil and mast cell desensitization. The intention is to understand the basic mechanisms of humanbasophil and mast cell mediator release in hopes of providing a firm framework on which future therapies for allergic disease can be based. One aspect of the mediator release mechanism is these cells' capacity for autoregulation through the process termed desensitization, and it is on this aspect which we will focus our efforts. Four areas are targeted for study. 1) elucidating the mechanism by which diisopropylfluorophosphate inhibits desensitization 2) defining the role of large scale aggregation of antigen and IgE in promoting desensitization 3) comparing mast cell and basophil desensitization 4) determining the effects of desensitization on two known activation event biochemistries, calcium flux and phospholipid turnover DFP has been found to inhibit basophil desensitization and enhances histamine release supporting the concept that desensitization regulates release. Studies are proposed which will use radiolabeled DFP or DFP analogs to isolate the enzyme(s) involved in desensitization. Previous studies suggested that the size of cell surface IgE-antigen aggregates determine the characteristics cell mediator release and desensitization. Experiments to substantiate this hypothesis involve comparing several well defined antigens for their ability to induce desensitization. Binding assays and microscopic fluorescent photo-bleaching techniques will be employed to characterize surface IgE redistribution under the influence of these antigens. Mast cells are central to the pathophysiology of allergic diseases. They can now be purified to near homogeneity. Studies are proposed which will determine whether non-specific desensitization occurs in these cells and how they process antigen-IGE aggregates during stimulation and desensitization. Previous studies suggested that the size of cell surface IgE-antigen aggregates determine the characteristics cell mediator release and desensitization. Experiments to substantiate this hypothesis involve comparing several well defined antigens for their ability to induce desensitization. Binding assays and microscopic fluorescent photo-bleaching techniques will be employed to characterize surface IgE redistribution under the influence of these antigens. Mast cells are central to the pathopysiology of allergic diseases. They can now be purified to near homogeneity. Studies are proposed which will determine whether non-specific desensitization occurs in these cells and how they process antigen-IgE aggregates during stimulation and desenstitization. Finally, studies are proposed which will investigate the occurrence of calcium translocation and phospholipid turnover in both mast cells and basophils. The effect of desensitization will then be examined.