The role of leukocyte traffic and activation in parturition.

OBJECTIVE: This review focuses on the contribution of immune cell trafficking and activities during the initial phase of activation in the process of parturition. Although uterine contractile activity has been the predominant focus for the mechanism that initiates labor, significant cellular and biochemical changes cause remodeling of the cervix well before term. A convergence of evidence suggests that inflammatory processes that involve prostaglandins, nitric oxide, cytokines, as well as systemic and paracrine endocrine mediators may enhance uterine contractility, promote ripening of the cervix, and thus constitute an integrative hypothesis for the initiation of labor.

METHODS: Techniques to study the uterus and cervix of pregnant and virgin C3H/HeN mice included light and fluorescence microscopy. Tissues were processed by histochemistry and immunofluorescence. Analytic approaches to enumerate macrophages and assess activation included quantitative stereologic morphometry and laser scanning cytometry.

RESULTS: The transition between relative quiescence of the uterus and enhanced contractility involved migration of macrophages from the uterine endometrium and activation of macrophages in the cervix. Before birth, macrophages migrate into the cervix and are activated in the myometrium.

CONCLUSION: Immune cell trafficking and activation are part of the initial mechanism that promotes ripening of the cervix, enhances uterine contractility, and initiates parturition. Markers for the conclusion of pregnancy may have diagnostic or therapeutic value to assess the normal progress of labor or identify women at risk of preterm labor.