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. I_-glucan, a major component of the yeast cell wall, is elaborated into the bloodstream of patients with systemiccandidiasis although the role of I_-glucan in the pathobiology of the disease is not clear. Recent findings from this laboratory have shown I_- glucan, converts PMN migration from random to directed. The conversion is mediated by recognition of 13- glucan by the leukocyte 132integrin CR3 (CD11 b/CD18) and is a previously unrecognized effect of 13-glucan on neutrophil function. The long term goal of our work is to understand how host defenses are affected by 13- glucan during the course of systemic fungal infections. The focus of the current proposal is to determine the mechanisms through which 13-glucan recognition by CR3 alters neutrophil function. Experiments in Aim I will investigate the role of several intracellular signalling pathways that, based on our current findings, are hypothesized to mediate the increased chemotactic capacity of neutrophils migrating on 13-glucan- supplemented matrix.
Specific Aim II will apply a well-characterized wound model to demonstrate the effect of _-glucan on the ability of the host neutrophils to respond to injury. In vitro findings have determined that activation of CR3 by _-glucan regulates the function of integrins of the 131 family. The wound model will determine whether 13-glucan and/or systemic candidiasis similarly alters the function of 131 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 signalling.
Specific Aim III will test the hypothesis that a novel pathway of _1 integrin crosstalk dissociates GPl-linked receptors from CR3 molecules. Since 13-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 13-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 I_-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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