Cytokines in placental physiology

Recent studies have shown that the human placenta is a very complex organ with many properties (Petraglia et al., 1990c). It plays a very important role in the physiology of pregnancy. Among various functions, its hormonal production is one of the most relevant. Other than the classical protein (human chorionic gonadotropin [hCG] and human placental lactogen [hPL]) and steroid hormones (progesterone, estradiol, estriol and estrone), it synthesizes hypothalamic-like neurohormones and neuropeptides (Petraglia et al., 1990a). Moreover, growth factors and cytokines are also produced in human placental cells and are able to influence the endocrine function. Cytokines are glycoproteins produced by a large variety of cells especially of the immune system. Hormonal-releasing properties of cytokines on hypothalamus, pituitary or on the other endocrine glands have been described (Bateman et al., 1989; Rivier et al., 1989). Some in vitro studies have shown that cytokines may also have a regulatory function on placental hormonal release. Moreover, placental cytokines may be involved in the immunoregulation of the maternal-fetal interface. It is suggested to be important for fetal survival with cytokines being the mediator of this phenomenon. It is not clear whether trophoblast or immune cells deriving from the circulation are the source of these glycoproteins found in placental extracts. Some reports indicate that macrophages are one of the major cell populations in the placenta, thereby supporting their role in producing cytokines (Flynn, 1982; Yagel et al., 1988).