The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings have not been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of the NTP or the U.S. Government.
The mono-nitrotoluenes are synthesized by the nitration of toluene. Meta-nitrotoluene is a clear, yellow liquid at ambient temperature. The mononitrotoluenes are slightly soluble in aqueous solution but are readily soluble in organic solvents. The nitrotoluenes have been detected in air, water, and soil. Meta- and para-nitrotoluene have been identified by the National Toxicology Program for detail study. M-nitrotoluene was the second mono-nitrotoluene to be investigated for its potential adverse actions on the immune system.
The objective of the studies reported here was to determine the potential immunotoxicity of m-nitrotoluene in mice exposed by the oral route. The studies were divided into three areas: the more standard toxicology studies provided the base against which to compare the immunology studies; the immunology studies provided data on specific cellular targets of the xenobiotic; and the host resistance studies were used for a global assessment of the ability of the exposed animal to resist pathogenic challenge.
Mice exposed to m-nitrotoluene by gastric gavage gained body weight over the 2 week experimental period to a slightly greater extent than the control groups. Of the selected organs weighed, the liver and kidney of mice exposed to m-nitrotoluene were increased in weight while the thymus weight was decreased. The liver of mice exposed to m-nitrotoluene, but not ortho-nitrotoluene (o-nitrotoluene), showed slight to moderate swelling of the hepatocytes adjacent to the central veins. The hepatocyte swelling appeared to be reversible and there was no evidence of necrosis. The selected hematological and serum chemistries were unaffected by m-nitrotoluene exposure. Bone marrow cellularity and the number of CFU/M and CFU/GM were unaffected by m-nitrotoluene exposure.
M-nitrotoluene suppressed the lgM response to sRBC and the DHR response to KLH. There was a slight (13%) decrease in the percentage of T lymphocytes in the spleen. The response to the T cell mitogens was suppressed by as much as 39.2%. FC mediated adherence and phagocytosis of chicken erythrocytes were increased dose-dependently in mice exposed to m-nitrotoluene. All of the other immune parameters were unaffected by exposure to m-nitrotoluene. These parameters included natural killer cell activity, response to mitogens and allogeneic cells, and serum complement and interferon levels.
Exposure of mice to m-nitrotoluene decreased resistance to Listeria monocytogenes. The decreased resistance to Listeria monocytogenes may be related to the decrease in the DHR to KLH. Resistance to Streptococcus pneumoniae and Plasmodium yoelii were unaffected. Resistance to the two tumor models the PYB6 tumor and the B16F10 melanoma was increased.
The three phases of these studies indicate that the liver and, to an equal or greater extent, the immune system are a target for toxicity of m-nitrotoluene. The decreased host resistance to Listeria monocytogenes can be attributed to the decrease in T lymphocytes and, as seen in the number and activity as expressed, to the decreased delayed hypersensitivity response to Keyhole limpet hemocyanin. The decrease in lgM response did not correlate with a host resistance model, most likely because no effect was seen on the lgG response. The increased resistance seen in the tumor models may be related to the increased macrophage activity; i.e., increase ectoenzyme activity and increased FC mediated adherence of chicken erythrocytes.
With the completion of the studies on m-nitrotoluene, three mono-nitrotoluenes were investigated. 0-nitrotoluene was used as a comparative control with the dose-response studies on m-nitrotoluene, and p-nitrotoluene was evaluated previously. Meta-and para-nitrotoluene produced greater actions on the immune system than ortho-nitrotoluene. Humoral and cell mediated immunity were affected. The delayed hypersensitivity response to Keyhole limpet hemocyanin was suppressed with m-and p-nitrotoluene. All three isomers produced a state of decreased resistance to Listeria monocytogenes.