Methylene dianiline (DDM) causes a dose- and time-dependent cholestasis, bile ductular epithelial injury, and hepatic parenchymal insult in rats. The mechanism of toxicity is unknown. Since hepatic leukocyte infiltration is a prominent feature of DDM-induced liver injury, and because leukocytes play a causal role in hepatic and extrahepatic tissue injury, we tested the hypothesis that toxicity caused by DDM is dependent on neutrophils or other circulating inflammatory cells. A polyclonal antibody (NAb) against rat neutrophils was used to address the role of the neutrophil in DDM-induced liver injury. NAb administration caused a significant reduction in circulating neutrophils without altering other leukocyte numbers. Moreover, NAb pretreatment prevented hepatic neutrophil infiltration after administration of DDM. However, neutrophil depletion did not afford protection from DDM-induced liver injury. This result was confirmed and the role of other circulating leukocytes was evaluated by inducing systemic leukopenia using cyclophosphamide (CYCLO). Administration of CYCLO diminished the number of circulating leukocytes within 4 days after treatment. Depletion of leukocytes by CYCLO prevented the hepatic accumulation of leukocytes but did not protect rats from DDM hepatotoxicity. These results suggest that the large numbers of leukocytes that infiltrate the liver after DDM administration do not contribute to hepatic injury.
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