Strong affinity of estradiol and its ligands for eosinophilic leucocytes in the rat and mouse uteri during the estrous cycle

The affinity of estradiol (E2) for eosinophils in the rat and mouse uteri during the estrous cycle was studied by light and electron microscope autoradiography (ARG). In in vivo ARG, in which the prefixed uteri were incubated at each stage of estrous cycle with 3H-E2 or its ligand 3H-moxestrol, the developed silver grains were localized on the specific granules of eosinophils. At the late estrus phase, eosinophils were frequently phagocytized by macrophage-like interstitial cells, whose phagosome included eosinophilic granules in various stage of degeneration covered with silver grains, and also showed positive reaction for acid phosphatase activity. Grain accumulation was inhibited when the tissue was incubated in 3H-E2 with a 100-fold excess of nonradioactive E2. When fresh frozen thin sections were incubated in 3H-E2, we succeeded in demonstrating the binding of E2 to the eosinophils in spleen, small intestine, blood and bone marrow. However, in in vivo ARG using the fresh thaw-mount technique, only the uterine eosinophils showed grain accumulation, and eosinophils of other tissues did not bind 3H-E2. Local eosinophilia was observed in the uterus of ovariectomized rats at one hr after E2 injection into the uterine wall. These results suggest that all eosinophils may have a strong affinity for E2, and that they are directly induced into the uterus by estrogen. Specific granules of eosinophils, which contain strong peroxidase enzymatic activity, seem to destroy the excess amount of E2 in the uterus at estrus, and then the eosinophils are phagocytized by the macrophage-like interstitial cells.