EMBRYONIC IMPLANTATION IN MICE IS BLOCKED BY INTERLEUKIN-1 RECEPTOR ANTAGONIST

We have investigated the relevance of interleukin-1 receptor type I (I L-1R tI) in the implantation process in vivo in a murine model. Indire ct immnunofluorescence experiments demonstrate that IL-1R tI is locate d in mouse endometrial lumenal epithelium with increased intensity in the periimplantation period, whereas IL-1 beta staining is located in the mouse placenta. PMSG/human CG (hCG)-stimulated and mated 12-week-o ld B6C3F-1 female mice were randomly allocated to three groups: A, con trol noninjected; B, buffer-injected animals; and C, animals injected ip with 20 mu g recombinant human IL-1 receptor antagonist (rhIL-1ra) every 12 h beginning on pregnancy day 3. Injections were continued unt il day 9, and animals were killed 12 h after the last injection. Pregn ancy rates in the three groups were: noninjected, 58.8% (10 of 17); bu ffer-injected, 73.7% (14 of 19); rhIL-1ra-injected, 6.7% (1 of 15), P = 0.0001155, Fisher exact test. To rule out the possibility that pregn ancy failure was due to an; embryotoxic effect of rhIL-1ra, 2-cell mou se embryos (n = 276) were flushed from the same group of animals used for in vivo experiments and cultured with increasing concentrations of rhIL-1ra: O mu g/ml (n = 91), 1 mu g/ml (n = 36), 50 mu g/ml (n = 36) , 100 mu g/ml (n = 52), and 200 mu g/ml (n = 61) rhIL-1ra. The percent ages of 2-cell mouse embryos reaching the blastocyst stage after 72 h in culture were 85.7%, 91.6%, 94.4%, 96%, and 85.2%, respectively. We further cultured these blastocysts for 5 days on fibronectin-coated pl ates with or without 200 mu g/ml rhIL-1ra. In both groups, hatching, a ttachment to fibronectin, outgrowth, and migration were documented to be similar. Furthermore, our longitudinal morphological study of embry onic implantation in control and rhIL-1ra-injected mice shows that the blockade of IL-1R tI interferes with the attachment of mouse blastocy sts to maternal endometrium in vivo. In summary, we demonstrate that b lockade of maternal endometrial IL-1R tI with IL-1ra prevents implanta tion in the mouse by interfering with embryonic attachment, without ad verse effects on blastocyst formation, hatching, fibronectin attachmen t, outgrowth, and migration in vitro.