The human corpus luteum: remodelling during luteolysis and maternal recognition of pregnancy.

The marked tissue remodelling associated with luteolysis involves increased expression and activity of matrix metalloproteinases (MMPs) and an influx of immune cells, notably macrophages. Since the corpus luteum expresses high concentrations of specific tissue inhibitors of MMPs, it is clear that it is not only the increased activity of MMPs that is important, but also their tissue localization. Human chorionic gonadotrophin inhibits both MMP expression and macrophage influx in the rescued corpus luteum of early pregnancy. However, macrophages and the main cellular sources of MMPs in the corpus luteum do not express LH-hCG receptors. Therefore, it is likely that products of the steroidogenic cells, which do express LH-hCG receptors, are involved in the differential paracrine regulation of MMP expression and macrophage influx during luteolysis and maternal recognition of pregnancy.