Cytokine networks in the uteroplacental unit: macrophages as pivotal regulatory cells.

A rich array of potent regulatory molecules has been identified in the uteroplacental unit. Most recently uncovered are the cytokines, families of polypeptides that establish intercellular communications, a paracrine effect, and often bind to synthetic cells in autocrine regulatory loops. Nearly all of the disparate maternal and fetal cell types in the uteroplacental unit are integrated into the cytokine network. The highly versatile macrophage, abundant in uteroplacental tissues, has emerged as a potentially pivotal cell type because of its unique ability to send and receive cytokine signals. Elevated levels of cytokines, possibly secreted when uteroplacental macrophages are activated by either bacterial endotoxins or receptor-bound cytokines, may compromise pregnancy. In particular, cytokines have been implicated in the induction of pre-term labor associated with infections. Intensive research is required to delineate the temporal patterns of cytokine synthesis that characterize pregnancy, to evaluate the events leading to normal and premature pregnancy termination and to establish protocols for therapeutic interventions in cases of infection.