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Updated: Aug 23, 2026
A Silicosis Mouse Model Established by Repeated Inhalation of Crystalline Silica Dust
Published on: January 6, 2023
Markers of macrophage differentiation in experimental silicosis
Pierre Misson1, Sybille van den Brûle, Virginie Barbarin
1Industrial Toxicology and Occupational Medicine, Université Catholique de Louvain, Belgium. pierre-damien.misson@toxi.ucl.ac.be
Abstract:
Macrophages are characterized by a marked phenotypic heterogeneity depending on their microenvironmental stimulation. Beside classical activation (M1), it has been shown that macrophages could follow a different activation pathway after stimulation with interleukin (IL)-4 or IL-13 (M2). Recently, it has been postulated that those "alternatively activated" macrophages may be critical in the control of fibrogenesis. In an experimental model of silicosis, where pulmonary macrophages play a central role, we addressed the question of whether lung fibrosis development would be associated with alternative macrophage activation. As available markers for alternative macrophage activation, type-1 arginase (Arg-1), Fizz1, Ym1/2, and mannose receptor expression were evaluated at the mRNA and/or protein levels at different stages of the disease. Nitric oxide synthase-2 (NOS-2) expression was also examined to investigate the classical counterpart. We found that the expression of Arg-1, Fizz1, and NOS-2 in adherent bronchoalveolar lavage cells was highly up-regulated 3 days after silica administration but returned to control levels during the fibrotic stage of the disease (60 days). By comparing the early response to silica in C57BL/6 and BALB/c mice, we observed that the amplitude of Arg-1 mRNA up-regulation was not associated with the severity of lung fibrosis. Using a model of manganese dioxide particles (resolutive alveolitis), we showed that this early Arg-1 mRNA was not specific to a fibrogenic lung response. Our data indicate that the modifications of M1/M2 marker expression are limited to the early inflammatory stage of silicosis and that the establishment of a fibrotic process is not necessarily associated with M2 polarization.
Insights
Lung fibrosis is not always linked to alternative macrophage activation (M2). Early M1/M2 marker changes in silicosis resolve before fibrosis fully develops, suggesting M2 polarization isn't essential for fibrotic processes.
Area of Science:
- Immunology
- Pulmonary Medicine
- Toxicology
Background:
- Macrophages exhibit diverse phenotypes (M1, M2) based on microenvironment.
- Alternatively activated (M2) macrophages are implicated in controlling fibrogenesis.
- Pulmonary macrophages are central to silicosis, a fibrotic lung disease.
Purpose of the Study:
- Investigate the association between lung fibrosis development and alternative macrophage activation in silicosis.
- Evaluate M1/M2 macrophage markers during different stages of experimental silicosis.
- Determine if M2 polarization is critical for fibrotic processes.
Main Methods:
- Used an experimental silicosis model in mice.
- Assessed mRNA and protein expression of M2 markers (arginase-1, Fizz1, Ym1/2, mannose receptor) and M1 marker (NOS-2).
- Analyzed macrophage markers at early (3 days) and late (60 days) stages of silicosis.
Main Results:
- Arginase-1, Fizz1, and NOS-2 expression increased early post-silica exposure but returned to baseline during the fibrotic stage.
- Early arginase-1 upregulation did not correlate with fibrosis severity.
- Early arginase-1 expression was also observed in a non-fibrogenic model (manganese dioxide), indicating lack of specificity.
Conclusions:
- M1/M2 marker expression changes in silicosis are confined to the early inflammatory phase.
- The development of lung fibrosis is not necessarily dependent on M2 macrophage polarization.
- Alternative macrophage activation is not a prerequisite for fibrotic lung disease establishment.
