Variation in macrophage migration inhibitory factor [MIF] immunoreactivity during bovine gestation

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine involved in several aspects of the immune response. MIF appears to play important roles in materno-fetal immuno-tolerance during placental establishment, modulation and growth as studied in epitheliochorial porcine and hemochorial human and mouse placentae. Here we studied the bovine placenta being multiplex, villous and synepitheliochorial with a low degree of invasion, to see if MIF could be involved. Placental tissues sampled from 12 cows at 9 stages of gestation (days 18-250), and endometrial tissues from two non-pregnant animals were processed for immunohistochemistry. Bovine MIF was detected by Western blot using anti-human MIF monoclonal antibodies. An immunoreactive band of approximately 12kDa confirmed similarities between bovine and human MIFs. Compared to the non-pregnant stage with very faint staining, the caruncular epithelium during pregnancy showed stronger staining for MIF. The intercaruncular epithelium in non-pregnant endometrium showed some reaction apically with increasing intensity at uterine gland openings; in contrast, at day 18 of gestation this staining was markedly increased. During gestation both caruncular and trophoblast epithelium of the placentomes were positive with different intensity in relation to the gestational stage. In the uterine glands, some strongly stained cells were present. The mature binucleated trophoblast giant cells were negative throughout pregnancy. During reestablishment of vascularisation, the vasculature in the caruncular area showed MIF reactivity. While supporting involvement of MIF in different placental types, the spatio-temporal variation in the bovine placenta suggests a regulatory role for MIF mainly in the interhemal barrier and during vascular development.