Adhesion receptors from the selectin, integrin and immunoglobulin gene families are thought to be instrumental in the normal and pathologic recruitment of all leukocytes; however, most studies have focused on neutrophils and acute inflammatory injury. Blockage of adhesion receptors involved in recruitment limits neutrophil-dependent injury in a number of model systems particularly in the lung. These successes raise hope that a similar approach will benefit chronic inflammatory and immune mediated diseases as well. However, adhesion receptors likely to be involved in the recruitment of mononuclear leukocytes, the key cellular mediators of these diseases, have not been adequately evaluated in physiologically relevant model systems. It is clear from neutrophil studies that leukocyte-endothelial adhesion must be studied under shear- stress to determine the contributions of individual adhesion molecules to recruitment in vivo. It is equally important to evaluate quantitatively the impact of receptor blockade on recruitment in relevant models of chronic inflammatory disease since in vitro modeling, at best, approximates flow conditions in vivo. Such studies are of fundamental importance to the development of therapeutics targeted at recruitment in chronic inflammatory/immunologic diseases. Our preliminary studies identify alpha4-containing integrins, most likely alpha4/Beta1, as a key receptor in the attachment of mononuclear leukocytes to cytokine-treated endothelium under shear. Depending on its basal level of binding activity, this receptor either strengthens attachment initiated by E- selectin or initiates attachment and recruitment. The former predominates for circulating cells co-expressing counter-receptors for the selectins and """"""""low avidity"""""""" alpha4 integrins. The latter predominates for circulating """"""""activated"""""""" monocytes and lymphoblasts generated in response to antigenic or inflammatory stimulate.
In Specific Aim 1 (SA 1), blocking monoclonal antibodies (mabs) specific for epitopes on the putative """"""""high avidity"""""""" form of the Beta1 chain and/or the alpha4/beta1 receptor will be generated in three species. These mabs will contribute to SAs 204. SA 2 will explore the interactions of E- Selectin, L-Selectin and the alpha4/Beta1 receptor during attachment of purified subsets of human monocular leukocytes and related cell lines to cytokine-activated endothelium at physiologic levels of linear shear- stress in vitro. SA 3 will explore the role of cellular activation in upregulating the function under shear and expression of activation epitopes on the alpha/beta receptor. SA 4 will use the newly developed and currently available Mabs specific for alpha4/beta1 receptor to determine the contribution of this receptor to mononuclear leukocyte recruitment in glycan-induced lung granulomas in the rat (collaboration with J. Warren, project III and P.A. Ward, project I) and schistosome- induced lung granulomas in the mouse (collaboration with S. Kunkel, project II).
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