MECHANISMS OF HUMAN LUNG HYPERSENSITIVITY REACTIONS

气道炎症在慢性哮喘中的核心作用已经得到认可

The central role of airway inflammation in chronic asthma has received increasing attention concordant with an alarming decade-long surge in asthma morbidity and mortality especially in urban populations where sizable numbers of asthmatics have elevated levels of IgE directed against indoor inhalants. The long term objective of this project is a better understanding of the cellular and molecular mechanisms of human lung allergic disorders and asthma, and means of their control. The human lung mast cell (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, triggers the pathophysiologic manifestations of the acute ("early phase," EPR) asthmatic response that results in immediate breathlessness. It is unknown what cell(s) directly produces the groundwork for chronic airway inflammatory ("late phase", LPR) responses characterized by leukocyte, especially eosinophil, infiltration of airways. The current view, principally based on cell samplings obtained well beyond the initial development of airway inflammation, is that the LPR is "driven" by Interleukin-4 and -5, the major cytokines responsible for IgE generation and eosinophilia, respectively, emanating from the "Th2" subtype of cD4+ T-lymphocytes. We hypothesize that the mast cell is the major contributor of "TH2" cytokines released within 2-4 hours following allergen challenge, and thus sets the framework for chronic inflammation. Over the past twelve years, techniques developed in our laboratory to purify HLMC have allowed for the first time, detailed studies of their biology. Also, we discovered and physically separated HLMC subpopulations distinguished by morphologies, histochemistry, and function. Recently, we have applied molecular hybridization and protein quantification techniques to identify the gene expression, protein release and temporal pattern of co-expression from purified HLMC and lung tissue, of Th2 cytokines. Moreover, we have begun to uncover pharmacologic mechanisms regulating gene expression and release of IL-5, including the annihilation of the IL-5 mRNA and protein responses by corticosteroids. Our specific aims are to define "Th2-like" cytokines in purified HLMC, HLMC subsets, and human lung tissue fragments, with respect to: identification, quantification, triggers, and their drug modulation including corticosteroids, and 13-agonists. Gene expression will be screened using reverse transcription polymerase chain reaction (RT-PCR), and RNase protection. Cellular attribution of cytokine generation will be performed by in situ hybridization and immunocytochemistry. Increased understanding of HLMC heterogeneity, Th2 cytokine generation from human lung and purified HLMC, and the capacity of specific drugs to target "inflammation" and the LPR, will broaden our understanding of human hypersensitivity, and influence the construction of therapies.