It is clear that the immune system and the reproductive system interact with and influence each other and that the immune system can have positive and negative regulatory effects on the outcome of pregnancy. The discovery of murine models of immunologically mediated spontaneous fetal resorptions has proved to be very useful for the study of immunological influences on pregnancy. In an attempt to elucidate the mechanisms underlying pregnancy impairment in one such "natural" model of pregnancy

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... s, we compared the expression of the cytokines tumor necrosis factor a, interferon r, and interleukin-2 in placental tissue from a resorption-prone strain combination with the expression from a normal combination. We found significantly enhanced expression of these three cytokines in placentas from the resorption-prone combination using dot-blot hybridization and Northern hybridizations. Since these cytokines are abortifacients in vivo and have detrimental effects on the placenta, and hence on fetal development and survival, our demonstration of enhanced expression of these deleterious cytokines may give insight into the mechanisms involved in immunologically mediated spontaneous abortions.