BIOCHEMICAL RELATIONSHIPS OF BASOPHILS AND EOSINOPHILS

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The developmental and biochemical relationships of human basophils and eosinophils and their functional interactions in allergic, parasitic, inflammatory and other diseases are unclear. Basophils and eosinophils may differentiate from a common progenitor, and certain presumably eosinophil specific membrane and cationic granule proteins have been found to be constituents of basophils, but not of neutrophils or mast cells. Some of these eosinophil granule-derived cationic proteins stimulate basophils and mast cells to release mediators of inflammation. To further elucidate interrelated aspects of the ontogeny, biochemistry, and function of human basophilic and eosinophilic leukocytes, the research will study: 1) the comparative localization, and physicochemical and biochemical properties of proteins common to these granulocytes, 2) the comparative biosynthesis, post-translational processing, and/or uptake of these proteins by mature peripheral blood-derived cells and immature cells during differentiation, and 3) the comparative mechanisms for cell activation and extracellular secretion of their common proteins. These studies will use basophils and eosinophils purified both from peripheral blood or from specifically induced cultures of human fetal cord blood mononuclear cells, homogeneously purified eosinophil and basophil proteins, and monospecific antisera to these proteins. Studies of the subcellular localization, enzymatic activity, uptake and secretion of Charcot-Leyden crystal protein (lysophospholipase), eosinophil granule major basic protein and eosinophil peroxidase in the basophil will utilize ultrastructural cytochemistry and autoradiography, immunoelectron microscopy, and specific radioimmunoassays. The biosynthesis, post-translational processing, and secretion of these proteins will be studied by metabolically labeling them in basophils and eosinophils during in vitro differentiation and maturation in cultures of fetal cord blood mononuclear cells induced to differentiate with basophil or eosinophil selective growth factors. Further, the intracellular activation of eosinophil peroxidase to facilitate its own proteolytic degradation via a hypochlorous acid-, chloramine-dependent mechanism, to generate some of the low Mr cationic proteins present in and secreted from the eosinophil granule will be investigated. These studies aim to provide a more integrated understanding of the myelopoietic, biochemical, and functional relationships of basophils and eosinophils, and to further define their dynamic interactions in the basophil/mast cell-eosinophil axis in allergic and related immunologic responses.