MECHANISMS OF HUMAN LUNG HYPERSENSITIVITY REACTIONS

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This project's long term objective is a better understanding of the mechanisms and control of human lung hypersensitivity disorders and asthma. Studies will focus on the central cell of lung hypersensitivity, the human lung mast cell (HLMC). The HLMC, by virtue of its anatomic localization, elaboration of potent chemical mediators upon stimulation, and the effects of these mediators on cell and tissue targets, can produce the pathophysiologic manifestations of these disorders: airway constriction, edema, and hypersecretion. The studies involve enzymatically dispersing human lung into a single cell suspension, and separating HLMC by elutriation and flotation through step-gradients into morphologically and functionally distinct subpopulations based on their diameters and densities, respectively. The density-step also results in purification of diameter separated HLMC. By taking advantage of typical histochemical profiles found after diameter and density separations, we have also recently developed methods to isolate HLMC subpopulations akin to the histochemically distinct subpopulations classically described in the rodent. Once isolated, HLMC subpopulations will be examined with respect to ultrastructure, content and release of mediators (including a recently discovered mast cell elastase), and sensitivities to relevant triggering stimuli. These stimuli include a newly described alvolar macrophage-derived releasing factor. Also, selective responsiveness of subpopulations to pharmacologic modulation of release will be examined. The agents to be tested include B-adrenergic agonists, inhibitors of arachidonic acid metabolism, membrane cholesterol binders, and cholesterol biosynthesis inhibitors. The crucial role of membrane cholesterol and phospholipids in release will be explored in purified HLMC through quantitative measurements of cholesterol and phospholipid turnover during activation-secretion. Novel mechanisms of HLMC release inhibition, through manipulation of the membrane lipid micro- environment, will also be studied.