Sex differences in the inflammatory immune response to multi-walled carbon nanotubes and crystalline silica

Abstract

Background: Respiratory disease is a leading cause of death and disability worldwide. These diseases frequently present with a sex bias in occurrence and severity, yet the mechanisms responsible for these sex biases is a critically understudied area of basic research.

Methods: Male and female C57BL/6 mice were exposed to multi-walled carbon nanotubes (MWCNTs) or crystalline silica (cSiO₂) via oropharyngeal aspiration. Acute assessments were conducted 24 h and 7 days after a single exposure. In chronic experiments, mice were exposed to respective particles once per week for 4 weeks and sacrificed 8 weeks after the last exposure. Lung lavage fluid (LLF) was assessed for markers of injury and inflammation. Immune cell populations were analyzed by flow cytometry and histopathology assessment was performed on lung tissue from chronically exposed mice.

Results: Female mice exposed to a single dose of MWCNTs generated a greater eosinophilic response than males 24 h and 7 days post-exposure. Eosinophilia was accompanied by elevated type 2 cytokine production in LLF. The exaggerated acute response in females was consistent with lung pathology observed in the chronic model: females had greater alveolitis and epithelial cell hyperplasia compared to males. There were no sex differences 24 h after cSiO₂ exposure, but by 7-day post-exposure female mice had greater airspace neutrophilia and inflammatory cytokine levels compared to males. However, following repeated exposure to cSiO₂, male mice had worse alveolitis and greater dendritic cell presence within the lungs.

Conclusions: Female mice are more susceptible to acute and chronic MWCNT-induced inflammation, but male mice are more susceptible to chronic cSiO₂-induced lung pathology.

Keywords:

• Multi-walled carbon nanotubes
• crystalline silica
• sex differences
• eosinophils
• lung inflammation

Acknowledgment

We would like to thank Dr. Nigel Walker and the National Toxicology Program of NIEHS for providing the MWCNTs and the Research Triangle Institute for the characterization of the MWCNTs. We would also like to thank Pam Shaw at the University of Montana’s Fluorescence Cytometry Core (Center for Environmental Health Sciences), and Mary Buford and Britten Postma in the Inhalation and Pulmonary Physiology Core (Center for Environmental Health Sciences) for technical assistance. The authors are indebted to Jack Harkema, DVM, PhD, DACVP of Michigan State University (Department of Pathobiology and Diagnostic Investigation) for performing the histopathology scoring assessments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Research reported in this publication was supported by the National Institute of Environmental Health Sciences under Award Number R01 ES023209 and the National Institute of General Medical Sciences under Award Number P30 GM103338. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.