Macrophage trafficking in the uterus and cervix precedes parturition in the mouse

Immune activation is implicated in the etiology of preterm labor, but littl e is known about macrophage number or distribution in the uterus or cervix at term. This study tested the hypothesis that macrophages migrate into the reproductive tract before the onset of parturition. Paraffin-embedded sect ions from the mid-uterine horn and cervix of C3/HeN mice on Days 15 and 18 of pregnancy, the day of birth (Day 19), and 1 day postpartum were stained with a pan-macrophage marker to analyze cell numbers and distribution. Duri ng pregnancy, uterine macrophages were dispersed in endometrium, usually as sociated with vasculature and subluminal epithelium. In myometrium, macroph ages were clustered in stromal connective tissue; near term and postpartum, cells appeared to surround the muscle bundles. Total macrophage numbers we re increased on Day 15 relative to those in nonpregnant controls, declined before birth, and increased postpartum. In the cervix, macrophages congrega ted in subepithelium, often perivascular or near ganglia. Macrophage number s in the cervix peaked on Day 18, then declined to nonpregnant levels by th e day after birth. Thus, macrophage numbers in the uterus were inversely re lated to those in the cervix. These findings raise the possibility that mac rophages and their products may be involved in uterine contractility and ce rvical remodeling during the processes of parturition.