BINDING-SITES FOR INTERFERONS ON OVINE AND HUMAN ENDOMETRIAL MEMBRANES

In the ewe, the major product of the preimplantation blastocyst is ovi ne trophoblast protein-1 (oTP-1), which is now classified as an omega- interferon (IFN). Receptors for IFN are present on sheep endometrium a nd vary cyclically, presumably modified by the actions of ovarian ster oids. This study examined whether or not IFN receptors were present on human endometrium at any stage during the menstrual cycle. In additio n, the steroid dependence of ovine endometrial IFN receptors was deter mined. Specific binding of I-125-labelled IFN (I-125-IFN) to ovine end ometrial membranes was substantially higher than binding to membranes derived from bovine spleen, human placenta or pooled human endometrium (relative specific binding 100:33:36:20). Human endometrial membrane preparations from proliferative-phase tissue showed very little specif ic binding (mean 0.8+/-0.3%, n=4) in contrast to luteal-phase endometr ium (2.1+/-0.3%, n=8). Treatment of ovariectomized ewes with oestradio l-17beta (E) resulted in significantly increased binding (117+/-7%) of I-125-IFN to endometrial tissues compared with tissue from ovariectom ized (OvX, 75+/-7%), progesterone (P)-treated (69+/-7%), or (E+P)-trea ted (81+/-8%) groups (P<0.05); all were compared with binding to poole d ovine luteal-phase tissue, 100%. There were no differences between t he other three groups. Scatchard analysis showed binding affinity of t he same order for the sheep and human receptors (Kd = 10(-10) mol L-1) but binding capacity was considerably lower for human (6.0 fmol mg-1) than for sheep (47-123 fmol mg-1) endometrium. These data suggest tha t interferons do not play as important a role in the establishment of pregnancy in the human as they do in the sheep.