The significant increase in numbers of ED2-positive macrophages in corpora lutea on estrus, as compared to proestrus, raises questions about the role of these cells in the tissue. The presence of ED2-pos-itive cells may indicate increased activation of macrophages. Determining the level of expression of major histocompatibility complex (MHC) II molecules on these cells might provide further evidence as to whether ED2-positive cells have enhanced functional status. Brannstram et al. reported increased levels of MHC II-positive cells on Day 15 of pseudopregnancy and after Day 15 of pregnancy in the rat. birth control yasmin
However, the incidence of MHC II-positive cells did not correlate with changes in ED2-positive cells. We have observed recently that the administration of dexamethasone to prolactin-treated hypophysectomized rats is associated with an increase in the number of ED2-positive cells present in the corpora lutea (based on personal communications). Dexamethasone has previously been shown to increase the number of ED2-positive colonies arising during culture of bone marrow stromal cells of rats, as has progesterone.