We investigated the effect of diesel exhaust (DE) on pregnancy and fetal development in mice at day 14 postcoitum (pc) with a special focus on the placenta. The number of absorbed fetuses increased in groups exposed to DE, and congestion was observed in histological sections of placentas. During placental absorption expression of CYP1A1 mRNA decreased to undetectable levels, whereas expression of TNF alpha mRNA increased approximately twofold over that of the control. Levels of CYP1A1 mRNA in normal placentas from DE-exposed mice were unchanged. mRNA levels of inflammatory cytokines IL-2, IL-5, IL-12 alpha, IL-12 beta, and GM-CSF increased in placentas exposed to DE (0.3 and 3.0 mg diesel exhaust particles (DEP)/m3). Expression of IL-5 mRNA was markedly increased in DE-exposed placentas, although levels were barely detectable in control placentas. IL-6 mRNA expression was increased approximately 10-fold in placentas exposed to DE (3.0 mg DEP/m3). It has been reported that expression of mRNA encoding proteins involved in immune function in the placenta is increased during fetal absorption in mice. In the present study, expression of such mRNA by the placenta was increased by DE exposure. Because it is believed that expression of mRNA in the placenta also affects fetal development, DE may promote fetal absorption. These findings suggest that in mice exposure to DE affects fetal absorption and placental function by modifying expression of immune-related genes during early gestation and expression of endocrine-related genes during late gestation.
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