Understanding the basis for pregnancy failure is an important medical/biological goal. The present study is designed to determine the role of intrauterine cytokine production by macrophages in endotoxin- induced abortion in mice. The mouse uterus contains high numbers of macrophages that are under the regulatory control of estrogen and progesterone. Control is mediated through hormone-induced local production of macrophage colony stimulating factor (CSF-l) by uterine epithelial cells. Uterine macrophage function, assessed by production of the pro- inflammatory cytokines, interleukin l (IL-I), interleukin 6 (IL-6) and tumor necrosis factor alpha (TNFalpha) is increased relative to non- reproductive organs. This is important, because the products of stimulated macrophages are positively and negatively involved in many pathologic processes, including endotoxin-induced toxicity. Pathologic responses are greatest when macrophages are exposed to multiple stimuli. For example, stimulation of macrophages with interferon gamma (IFNgamma) does not result in significant pathology, but prestimulation of macrophages with IFNgamma greatly increases endotoxin-induced effects. Endotoxin produces abortions in mice at dose levels that are not clinically toxic for adults. We hypothesized that the abortifacient ability of endotoxin might be related to the heightened responsiveness of normal uterine macrophages that could occur as a results of their having been prestimulated with ovarian hormones and CSF-1. We further hypothesized that abortion might result from overproduction in the uterus of toxic products of macrophages such as TNFgamma. To test these hypotheses, we propose to quantitate IL- 1, IL-6 and TNFalpha mRNA, bioactivity and immunoreactivity (ELISA) in uterus, liver, spleen, placenta and fetus before and after exposure of mice to abortion-producing regimens of endotoxin. Statistical comparisons will be made between untreated pregnant mice and mice treated with endotoxin or non-toxic endotoxin to determine the relationship of cytokine levels to pregnancy success. To test the hypothesis that individual cytokines cause abortions, we will determine whether mice can be protected from endotoxin-induced abortion by treating them with TNFalpha antibody or IL-1r antagonist. Since the studies are based on the rationale that endotoxin induces macrophages to produce cytokines, studies will be performed to determine if endotoxin-induced cytokine production is macrophage-dependent. In vitro studies with cell lines and in vivo studies with ovariectomized mice will be performed to evaluate the hypothesis that uterine macrophages, preconditioned by exposure to the physiologic stimuli, estradiol- 17beta, progesterone and CSF-1, exhibit heightened responses to endotoxin . These studies will provide increased understanding of the basis for fetal failure.