[Immunological analysis of the mechanism of maternal tolerance of a fetus and the cytokine-mediated regulation of feto-placental functions].

Recent analysis of a various kinds of cytokines revealed that the cytokines are actively involved in a number of important biological functions including immunological and endocrine functions. The present study investigated the unique cytokine-mediated immunological and endocrinological functions in the intra-uterine space during pregnancy. A human placenta which expresses paternal and maternal antigens was revealed to escape from maternal immune systems by releasing immunosuppressive cytokines derived from the placenta. Placental cytokines such as interleukin-6 (IL-6) activated IL-6-receptor-mediated signal transduction pathways to produce human chorionic gonadotropin (hCG). IL-1 and tumor necrosis factor-alpha (TNF-alpha) synergistically augmented IL-6 production to stimulate hCG production. However, transforming growth factor-beta (TGF-beta) suppressed these cytokine-mediated hCG production as well as IL-6 production. Thus, these placental cytokines, mainly derived from trophoblasts, cooperatively contributed to hCG production. IL-8 and monocyte chemotactic and activating factor (MCAF) activate host defense mechanism by activating neutrophils and monocytes as well as macrophages, respectively. IL-6 also activates immune responses and promote synthesis of acute-phase reactant proteins, contributing to augmentation of host defense mechanism in a different way from IL-8 and MCAF. Human placenta in the 3rd trimester actively produced these cytokines for potentiation of placental defense mechanism during pregnancy and in chorioamnionitis. A fetus in chorioamnionitis also produced these cytokines in utero for potentiation of fetal defense mechanism. Among these cytokines, IL-8 in a cord serum was a very sensitive and useful marker for clinical diagnosis of chorioamnionitis. Cord serum IL-6, in contrast, stimulated the synthesis of surfactant protein-A (SP-A) to promote fetal lung maturation and reduce the incidence of RDS. Collectively, the present study revealed the cytokine network in the placenta regulating maternal immune responses, placental endocrine functions, feto-maternal defense mechanism and fetal respiratory maturation.