Localization and characterization of macrophages in murine uterus

Macrophages are known to be present in the murine uterus and are known to be among those cells comprising the uterine decidual response to pregnancy. The extent of macrophage involvement in the decidual response has not been documented, and there are unresolved questions regarding expression of markers normally associated with macrophages on cells within the decidua. Using tissue immunohistology, macrophages were identified in virgin and pregnant murine uteri. A significant increase in macrophage density was noted during all stages of pregnancy. When uteri from virgin and pregnant mice were enzymatically digested, 10% of uterine cells from virgin and 22% from pregnant mice expressed macrophage markers (binding of rabbit antimouse macrophage serum, Fc gamma receptor expression). Double labeling immunofluorescence demonstrated that the two markers were associated with the same cells. Those results were confirmed in "panning" experiments using a monoclonal antimouse macrophage reagent. In cell suspensions from pregnant murine (C3H/HeN) uteri, 50% of cells exhibiting macrophage markers were I-Ak positive, and macrophages accounted for nearly all I-Ak positive cells in uterine cell suspensions. The results of this study demonstrate that the murine decidual response to pregnancy includes an increase in Fc gamma receptor-bearing macrophages and that a relatively high percentage of those macrophages are Ia positive.