title: Macrophage internalization of fungal beta-glucans is not necessary for initiation of related inflammatory responses.
abstract: Cell wall beta-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 beta-glucans should enhance our understanding of innate immune responses to fungi. In this study, we demonstrated that internalization of fungal beta-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 beta-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, beta-glucan-induced NF-kappaB 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 beta-glucan particles following actin disruption. Dectin-1, a major beta-glucan receptor on macrophages, colocalized to phagocytic cups on macrophages and exhibited tyrosine phosphorylation after challenge with beta-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 beta-glucan particles and cytokine release in response to the fungal cell wall component.
authors.affiliation: Thoracic Diseases Research Unit, Division of Pulmonary, Critical Care and Internal Medicine, Department of Medicine, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
authors.forename: Frances
authors.initials: F
authors.lastname: McCann
authors.forename: Eva
authors.initials: E
authors.lastname: Carmona
authors.forename: Vishwajeet
authors.initials: V
authors.lastname: Puri
authors.forename: Richard E
authors.initials: RE
authors.lastname: Pagano
authors.forename: Andrew H
authors.initials: AH
authors.lastname: Limper
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002473:Cell Wall / Q000737:chemistry; D002478:Cells, Cultured; D015638:Cytochalasin D / Q000494:pharmacology; D016207:Cytokines / Q000378:metabolism; D005452:Fluoresceins / Q000378:metabolism; D018836:Inflammation Mediators / Q000378:metabolism*; D037181:Lectins, C-Type; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010587:Phagocytosis / Q000187:drug effects; D010766:Phosphorylation; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism; D047071:beta-Glucans / Q000378:metabolism*; D000099181:Dectin-1
chemical_list: D000199:Actins; D015638:Cytochalasin D; D016207:Cytokines; D005452:Fluoresceins; D018836:Inflammation Mediators; D037181:Lectins, C-Type; D008565:Membrane Proteins; D016328:NF-kappa B; D009419:Nerve Tissue Proteins; D014409:Tumor Necrosis Factor-alpha; D014443:Tyrosine; D047071:beta-Glucans; D000099181:Dectin-1; C505459:5-((4,6-dichlorotriazin-2-yl)amino)fluorescein hydrochloride-Celite complex-labeled Saccharomyces cerevisiae beta-glucan