Analysis of the number and distribution of macrophages, lymphocytes, and granulocytes in the mouse uterus from implantation through parturition.

The metrial gland and decidua basalis are uterine structures which, during pregnancy in mice and rats, contain bone marrow derived cells. The current study demonstrates that large numbers of bone marrow derived cells, identified by common leukocyte antigen (CLA) positivity, accumulate in the mesometrial uterus between days 6 and 10 and contribute significantly to the cellularity of both the metrial gland and the decidua basalis. The distribution of F4/80+ cells (macrophages) is similar, suggesting that CLA+ cells in the metrial gland and decidua basalis are macrophages. Disappearance of luminal epithelium in the mesometrial uterus between days 11 and 12 leads to regression of metrial gland and decidua basalis and coincident disappearance of CLA+ and F4/80+ cells. A second population of CLA+ and F4/80+ cells appears in association with the development of new uterine luminal epithelium which surrounds the fetus and placenta during the final week of pregnancy. These very large accumulations of macrophages invariably are related to presence of epithelium.