Polymorphonuclear leukocytes (PMN) are an inherently motile cell type, which can be directed to move up a chemoattractant gradient. Chemotactic movement is essential for PMN accumulation at sites of tissue injury or infection, however, mechanisms which provide the navigational signals needed to give direction to these cells are incompletely understood. Candida albicans is the fourth leading cause of nosocomial infections with post-surgical, trauma and immunosuppressed patients being at highest risk. Beta-glucan, a major component of the yeast cell wall, is elaborated into the bloodstream of patients with systemic candidiasis although the role of beta-glucan in the pathobiology of the disease is not clear. Recent findings from this laboratory have shown beta-glucan, converts PMN migration from random to direct. The conversion is mediated by recognition of beta-glucan by the leukocyte beta2integrin CR3 (CD11 b/CD18) and is a previously unrecognized effect of beta-glucan on neutrophil function. The long-term goal of our work is to understand how host defenses are affected by beta-glucan during the course of systemic fungal infections. The focus of the current proposal is to determine the mechanisms through which beta-glucan recognition by CR3 alters neutrophil function. Experiments in Aim I will investigate the role of several intracellular signaling pathways that, based on our current findings, are hypothesized to mediate the increased chemotactic capacity of neutrophils migrating on beta-glucan supplemented matrix.
Specific Aim II will apply a well-characterized wound model to demonstrate the effect of beta-glucan on the ability of the host neutrophils to respond to injury. In vitro findings have determined that activation of CR3 by beta-glucan regulates the function of integrins of the beta1 family. The wound model will determine whether beta-glucan and/or systemic candidiasis similarly alters the function of beta1 integrins in mediating PMN entry into a site of injury. Finally, several proinflammatory mediators (LPS, immune complexes, urokinase plasminogen activator) bind to glycosylphosphatidylinositol (GPI)-Iinked receptors (CD14, CD16, CD87), which in turn rely on CR3 for intracellular signaling.
Specific Aim III will test the hypothesis that a novel pathway of beta1 integrin crosstalk dissociates GPl-linked receptors from CR3 molecules. Since beta-glucan and GPl-linked receptors share a common CR3 binding site, dissociation of GPl-linked receptor from CR3 would simultaneously increase the number of CR3 molecules available for beta-glucan binding and blunt the response to ligands specific for GPl-linked receptors. The proposed studies will further elucidate the mechanism of action through which beta-glucan primes neutrophils both as a component of systemic fungal infections and as a biological response modifier with therapeutic potential for treating polymicrobial sepsis.
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