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Species and strain comparisons of immunosuppression by 2-methoxyethanol and 2-methoxyacetic acid
R J Smialowicz1, M M Riddle, W C Williams
1Environmental Toxicology Division, Health Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711.
Abstract:
2-Methoxyethanol (ME) and its principal metabolite 2-methoxyacetic acid (MAA) have been shown in our laboratory to be immunosuppressive in male Fischer 344 rats. In this study several strains of 12-week-old female rats and mice were used to compare the immunosuppressive activity of equimolar concentrations of ME and MAA on the trinitrophenyl-lipopolysaccharide (TNP-LPS) antibody plaque-forming cell (PFC) response, which we previously demonstrated to be a sensitive end point. Female inbred Lewis, Fischer 344 and Wistar/Furth, and outbred Sprague-Dawley rats were dosed by gavage with either ME or MAA at dosages of 0.33 to 2.64 mmol/kg/day for 10 consecutive days. Female inbred C3H and C57BL/6J, hybrid B6C3F1, and outbred CD-1 mice were similarly dosed with equimolar dosages of 0.66 to 5.28 mmol/kg/day ME or MAA. All animals were immunized on day 9 of dosing and PFC responses evaluated 3 days later. Suppression of the PFC response was observed in all strains of rats at 2.64 mmol/kg/day ME or MAA. Lewis and Wistar/Furth rats were found to be the most sensitive strains with suppression at levels as low as 0.66 mmol/kg/day ME or MAA. While ME and MAA dosing resulted in suppression of the TNP PFC response in all the rat strains tested, such treatment did not suppress this PFC response in any of the mouse strains examined. These results indicate that under the conditions of this study rats, but not mice, are immunosuppressed by ME and MAA exposure, and that the susceptibility to immunosuppression differs among rat strains.
Insights
Exposure to 2-methoxyethanol (ME) and 2-methoxyacetic acid (MAA) suppressed the immune response in female rats but not in mice. Susceptibility varied among rat strains, with Lewis and Wistar/Furth rats being most sensitive to immunosuppression.
Area of Science:
- Toxicology
- Immunology
Background:
- 2-Methoxyethanol (ME) and its metabolite 2-methoxyacetic acid (MAA) are known immunosuppressants in male rats.
- The trinitrophenyl-lipopolysaccharide (TNP-LPS) antibody plaque-forming cell (PFC) response is a sensitive indicator of immunosuppression.
Purpose of the Study:
- To compare the immunosuppressive activity of ME and MAA in female rats and mice.
- To identify potential differences in susceptibility among various rat and mouse strains.
Main Methods:
- Female rats (Lewis, Fischer 344, Wistar/Furth, Sprague-Dawley) and mice (C3H, C57BL/6J, B6C3F1, CD-1) were dosed with ME or MAA for 10 days.
- Animals were immunized, and the TNP-LPS PFC response was evaluated to assess immunosuppression.
Main Results:
- All tested rat strains showed suppressed PFC responses at the highest ME/MAA doses (2.64 mmol/kg/day).
- Lewis and Wistar/Furth rats exhibited immunosuppression at lower doses (0.66 mmol/kg/day).
- No immunosuppressive effects of ME or MAA were observed in any mouse strains.
Conclusions:
- Female rats are susceptible to the immunosuppressive effects of ME and MAA, unlike mice.
- Significant strain-dependent differences in immunosuppressive susceptibility exist among rat populations.