Our goal is to define a possible """"""""common receptor defect"""""""" which results in many neutrophil functional alterations reported for patients suffering from Localized Juvenile Periodontitis (LJP). In this study, we propose to identify and characterize common structural and functional motifs among similar neutrophil (PMN) membrane components such as the receptors for IL-8, C5a, and FMLP. We also propose to characterize a functional profile of PMN from LJP patients in response to IL-8, and the closely related chemotactic cytokines NAP-2 and GRO/MGSA. The receptors for IL- 8, C5a, and FMLP play a critical role in cell activation, and have been reported by various investigators to be """"""""altered"""""""" in PMN of patients with LJP. The receptors for these chemoattractants share some structural and functional features such as molecular arrangement in the membrane, effects on cell response, and/or membrane signal transmission and ligand interactions. We hypothesize that in LJP there is a common underlying cell-associated defect, either at the receptor level, or at post receptor/membrane level. We further propose that this molecular defect may contribute to the altered PMN response reported for these patients and their siblings.
Our specific aims are to characterize the functional domains of the human interleukin-8 (IL-8) receptor which are involved in ligand binding and in signal transduction through activation of G proteins. The IL-8 receptor was selected as a model since its ligand (IL-8) is involved in most PMN responses to bacterial infections and inflammation, and we hypothesize that it is a central cytokine in modulating periodontal infections. This functional characterization will be carried out by: a) constructing synthetic peptides corresponding to different portions of the IL-8 receptor molecule, and b) site-directed mutagenesis and functional characterization of mutated recombinant receptor. We also propose to define the chromosomal localization of the coding region(s) of the IL-8 receptor. Understanding the functional domains as well as the structural and genetic organization of this receptor will lead to better understanding of PMN function in host responses, as well as basic mechanisms of cell activation. To begin the search for a """"""""common denominator defect"""""""", we propose to characterize a functional profile of LJP PMN in response to IL-8, and the functionally similar chemotactic cytokines NAP-2 and GRO/MGSA, with particular emphasis on ligand binding, receptor distribution, and transmembrane signaling. We will then correlate these profiles with expression of FMLP and C5a receptors. These studies are designed to provide a better understanding of abnormalities in LJP neutrophils and the role they play in disease susceptibility. In addition, knowledge of the IL-8 receptor functional domains may allow design of agonists or antagonist peptides with the potential to modify IL-8 induced inflammatory reactions. The strength of this proposal is the combination of a basic molecular biological approach with clinical studies of a large number of well characterized LJP patients.
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