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Infection and Immunity, October 2005, p. 6340-6349, Vol. 73, No. 10
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.10.6340-6349.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Macrophage Internalization of Fungal ß-Glucans Is Not Necessary for Initiation of Related Inflammatory Responses

Thoracic Diseases Research Unit, Division of Pulmonary, Critical Care and Internal Medicine, Department of Medicine,¹ Department of Immunology,² Department of Biochemistry & Molecular Biology, Mayo Clinic College of Medicine, Rochester, Minnesota 55905³

Received 28 January 2005/ Returned for modification 3 March 2005/ Accepted 2 June 2005

Cell wall ß-glucans are highly conserved structural components of fungi that potently trigger inflammatory responses in an infected host. Identification of molecular mechanisms responsible for internalization and signaling of fungal ß-glucans should enhance our understanding of innate immune responses to fungi. In this study, we demonstrated that internalization of fungal ß-glucan particles requires actin polymerization but not participation of components of caveolar uptake mechanisms. Using fluorescence microscopy, we observed that uptake of 5-([4,6-dichlorotriazin-2-yl] amino)-fluorescein hydrochloride-Celite complex-labeled Saccharomyces cerevisiae ß-glucan by RAW macrophages was substantially reduced in the presence of cytochalasin D, which antagonizes actin-mediated internalization pathways, but not by treatment with nystatin, which blocks caveolar uptake. Interestingly, ß-glucan-induced NF-B translocation, which is necessary for inflammatory activation, and tumor necrosis factor alpha production were both normal in the presence of cytochalasin D, despite defective internalization of ß-glucan particles following actin disruption. Dectin-1, a major ß-glucan receptor on macrophages, colocalized to phagocytic cups on macrophages and exhibited tyrosine phosphorylation after challenge with ß-glucan particles. Dectin-1 localization and other membrane markers were not affected by treatment with cytochalasin D. Furthermore, dectin-1 receptors rather than Toll-like receptor 2 receptors were shown to be necessary for both efficient internalization of ß-glucan particles and cytokine release in response to the fungal cell wall component.

Editor: T. R. Kozel

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