Monocytosis and monocytic infiltration of decidua in early pregnancy.

This study showed a marked increase of blood monocytes in the 7th-20th week of pregnancy. The highest monocyte values were observed in the very first weeks whereas neutrophil counts were increasing throughout the observation period. No significant pregnancy associated changes were found in T-cell subpopulations or in HLA-DR expression by monocytes. First trimester decidual tissue contained many HLA-DR, Leu-M3 positive cells. Their distribution was patchy and mainly confined to areas of prominent decidual reaction. In contrast normal secretory phase endometrium showed only occasional Leu-M3, HLA-DR positive cells but a few clusters of glandular epithelial cells expressed HLA-DR. Culture supernatants from both decidual and secretory endometrial tissues contained PGE2 in concentrations known to suppress PHA lymphocyte responses in vitro. We postulate that monocytes infiltrating the decidual tissue may, possibly through PGE2 mediated immunosuppression, help to prevent rejection of the fetal allograft early in pregnancy.