title: Silica-directed mast cell activation is enhanced by scavenger receptors.
abstract: Inhalation of crystalline silica results in pulmonary fibrosis and silicosis. It has been suggested that mast cells play a role in these conditions. How mast cells would influence pathology is unknown. We thus explored mast cell interactions with silica in vitro and in B6.Cg-kit(W-sh) mast cell-deficient mice. B6.Cg-kit(W-sh) mice did not develop inflammation or significant collagen deposition after instillation of silica, while C57Bl/6 wild-type mice did have these findings. Given this supporting evidence of a role for mast cells in the development of silicosis, we examined the ability of silica to activate mouse bone marrow-derived mast cells (BMMC), including degranulation (beta-hexosaminidase release); production of reactive oxygen species (ROS) and inflammatory mediators; and the effects of silica on Fc epsilon RI-dependent activation. Silica did not induce mast cell degranulation. However, TNF-alpha, IL-13, monocyte chemotactic protein-1, protease activity, and production of ROS were dose-dependently increased after silica exposure, and production was enhanced after Fc epsilon RI stimulation. This mast cell activation was inhibited by anti-inflammatory compounds. As silica mediates some effects in macrophages through scavenger receptors (SRs), we first determined that mast cells express scavenger receptors; then explored the involvement of SR-A and macrophage receptor with colleagenous structure (MARCO). Silica-induced ROS formation, apoptosis, and TNF-alpha production were reduced in BMMC obtained from SR-A, MARCO, and SR-A/MARCO knockout mice. These findings demonstrate that silica directs mast cell production of inflammatory mediators, in part through SRs, providing insight into critical events in the pathogenesis and potential therapeutic targets in silicosis.
authors.affiliation: Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892-1881, USA. jmbrown@niaid.nih.gov
authors.forename: Jared M
authors.initials: JM
authors.lastname: Brown
authors.forename: Emily J
authors.initials: EJ
authors.lastname: Swindle
authors.forename: Nataliya M
authors.initials: NM
authors.lastname: Kushnir-Sukhov
authors.forename: Andrij
authors.initials: A
authors.lastname: Holian
authors.forename: Dean D
authors.initials: DD
authors.lastname: Metcalfe
mesh_terms: D000818:Animals; D017209:Apoptosis; D001854:Bone Marrow Cells / Q000378:metabolism / Q000502:physiology*; D015550:Cell Degranulation; D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000378:metabolism; D003094:Collagen / Q000378:metabolism; D018793:Interleukin-13 / Q000378:metabolism; D008407:Mast Cells / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017382:Reactive Oxygen Species / Q000378:metabolism; D017455:Receptors, IgE / Q000378:metabolism; D011971:Receptors, Immunologic / Q000235:genetics / Q000378:metabolism; D051117:Scavenger Receptors, Class A / Q000235:genetics / Q000378:metabolism*; D012822:Silicon Dioxide / Q000633:toxicity*; D012829:Silicosis / Q000473:pathology*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: C491768:Ccl2 protein, mouse; D018932:Chemokine CCL2; D018793:Interleukin-13; C092228:Marco protein, mouse; D017382:Reactive Oxygen Species; D017455:Receptors, IgE; D011971:Receptors, Immunologic; D051117:Scavenger Receptors, Class A; D014409:Tumor Necrosis Factor-alpha; D012822:Silicon Dioxide; D003094:Collagen