Invasive fungal infections are emerging as a significant cause of morbidity and mortality, especially among the increasing immunosuppressed patient populations. Transition to a filamentous hyphal morphology, which is not easily cleared by phagocytosis, correlates strongly with invasiveness and virulence. This dissertation explored the effects of β-glucan, a component of the pathogenic yeast cell wall, on human polymorphonuclear leukocyte (PMN) respiratory burst, migration and mechanosensing as mediated through the β2 integrin, CR3 (αMβ2).
CR3 is a known β-glucan receptor via a lectin-like domain. These and other studies from our laboratory have shown that β-glucan accelerates chemotaxis of PMNs when added to a fibronectin (Fn) matrix. We show that immobilized β-glucan stimulates plasma membrane-associated respiratory burst, which is inhibited by Fn. β-glucan was shown to exhort its PMN priming effects through CR3 modulated in part through a system of β1-to-β2 integrin cross talk with VLA3 (α3β1) and VLA5 (α5β1). A putative mechanism through p38 MAPK and Lyn PTK is proposed.
We show that PMN migration on the CR3 ligand fibrinogen is independent of substrate stiffness, unlike the β1-mediated migration of PMNs on Fn. Migration in the presence of soluble β-glucan significantly increased PMN polarity index and significantly reduced the percentage of PMNs that initiated a respiratory burst before reaching the chemoattractant source.
Taken together, these data suggest that activation of β1 integrins and priming by β-glucan elaborated by a fungal infection may determine an inflammatory cell phenotype that is well suited to eliminate the virulent, filamentous form of fungi by accelerating chemotaxis towards the foci of infection while suppressing the premature release of oxidants until the neutrophil establishes direct multifocal contact with hyphae.
Additionally, fluorescence resonance energy transfer (FRET) based reporter constructs for CR3 activation and avidity were generated that provide evidence for conformational changes in the cytoplasmic domains of CR3 during physiologic activation, as well priming with soluble β-glucan. We also extended this by developing a differentiated HL-60 system that allows for the tracking of CR3 dynamic regulation during relevant PMN cellular functions.
|Advisor:||Reichner, Jonathan S.|
|School Location:||United States -- Rhode Island|
|Source:||DAI-B 71/11, Dissertation Abstracts International|
|Keywords:||Beta-glucan, Beta2 integrin, CR3, Fungal pathogen, Innate immune functions, Molecular pattern, Polymorphonuclear leukocytes|
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