Immunotoxicity Assessment of Multiwalled Carbon Nanotubes Following Whole-Body Inhalation Exposure for 30 and 90 Days of in B6C3F1/N Mice and 30 Days in HSD:Harlan Sprague Dawley SD® Rats

Victor J Johnson^1*Nigel J Walker²Michael I Luster¹Gary R Burleson¹Michelle Cora²Gregory L Baker³Barney Sparrow⁴Dori Germolec^2*

• ¹Burleson Research Technologies, Inc., Morrisville, NC, United States
• ²Division of Translational Toxicology, National Toxicology Program, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC, United States
• ³Sarepta Therapeutics, Columbus, OH, United States
• ⁴Battelle Memorial Institute, Columbus, OH, United States

Background: Several lines of evidence have suggested the possibility that inhalation exposure to multi-walled carbon nanotubes (MWCNT) at occupationally relevant doses can lead to systemic immunotoxicity. To test this hypothesis, we undertook in-depth examination of immune function in mice and rats exposed by inhalation to relatively low levels of 1020 Long Multiwalled Carbon Nanotubes (L-MWNT-1020).Methods: Studies were conducted to determine the systemic and pulmonary immunotoxic effects in mice and rats exposed to L-MWNT-1020 following whole-body inhalation for 6 hours/day for 5 days/week for 30 (mice and rats) and 90 (mice) days at dose levels of 0, 0.06, 0.2 and 0.6 mg/m 3 . Additional groups were administered cyclophosphamide (CPS) as a positive control for each cohort. Following exposure, pulmonary macrophage activity, immunophenotypic analysis of immune cells populations in the spleen, and systemic immune function, including tests for humoral (T-dependent antibody response, TDAR), cell-mediated (cytotoxic T-lymphocyte [CTL] activity), and innate (Natural Killer [NK] cell activity) immunity were conducted.Results: While exposure increased pulmonary macrophage activity, no major changes were observed in any of the systemic immune parameters measured in mice exposed for 30 or 90 days.In rats, there was a slight decrease in humoral immunity coinciding with an increase in the number of splenic T cell and NK cell populations.Conclusion: Although pulmonary macrophage activity increased in mice following exposure to L-MWNT-1020, systemic immune function for the most part remained unaffected. In contrast, rats demonstrated a slight decrease in humoral immune function as well as an increase in spleen cell numbers, T cell, and NK cell populations suggesting species-specific effects on systemic immunity, however, these effects were small and their biological significance with respect to altering disease susceptibility is unclear.