HUMAN MAST CELL AND BASOPHIL ARACHIDONIC ACID METABOLISM

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Human mast cells and basophils are central elements in numerous allergic disorders, such as hay fever, some forms of asthma, and anaphylaxis. When activated by allergens or other stimuli, these cells release a variety of proinflammatory chemical mediators. Among the most potent of these molecules are oxygenated products of arachidonic acid (AA), such as prostaglandins (PGs) and leukotrienes (LTs), including the leukotrienes (C, D and E) which compromise slow reacting substance of anaphylaxis. We have recently developed methods for highly purifying human lung mast cells and basophils, and have begun to characterize the spectrum of AA metabolites produced by these cells, and physiologic and pharmacologic mechanisms by which the release of these proinflammatory substances can be controlled. The central aim of this proposal is to further characterize AA metabolism in human mast cells and basophils in the hope that this information will lead to new approaches to the treatment of these disorders, by manipulating the synthesis and release of AA metabolites. Using a recently characterized, highly specific radioimmunoassay with confirmation by high performance liquid chromatography, we will determine if mast cell and/or basophil triggering leads to the production of leukotriene B4, a potent chemotactic chemokinetic, and activating factor for human neutrophils; we suggest that the release of this material prolongs the initial inflammatory response initiated by mast cell/basophil triggering. We will prepare and characterize mast cells from human synovial tissue from patients with inflammatory arthropthies, and compare them with human mast cells previously characterized in our laboratory. We suggest that mast cells are important in the pathogenesis of inflammatory joint disease, and that human mast cells from different tissues sites (synovial tissue vs lung) will differ in terms of factors which activate them, the profile of AA metabolites that they release, and ways in which their function can be modulated pharmacologically. We will define the spectrum of AA metabolites produced by human basophils after prelabelling them with 3H-AA; we hypothesize that they will produce cyclooxygenase metabolites, in addition to leukotriene C4 that we have shown previously, and suggest that triggers which cause the release of histamine but not leukotrienes (e.g. C5a) will cause a different pattern of phospholipid turnover than triggers which cause release of histamine and leukotrienes (e.g. antigen, anti-IgE, ionophore A23187). With these new insights into the metabolism of AA in human mast cells and basophils, we feel that clinically useful approaches to the treatment of allergic disorders, such as asthma, will result.