Early and efficient detection of embryonic death (ED) has a valuable impact as important as early pregnancy diagnosis in ruminants. Among early pregnancy diagnosis methods, detection of the expression of interferon tau stimulated genes (ISGs) in peripheral blood leukocytes (PBLs) is well documented in cows and ewes. Therefore, we hypothesized that the expression profile of ISGs in PBLs might also be useful for detecting ED in these animals. For this purpose, pregnant ewes were used as an experimental model. Pregnancy was detected on Day 18 after mating by transrectal ultrasonography. Pregnant ewes were divided into a control group (sham injection on Day 18, n = 10) and ED group (treated with 75 mu g synthetic PGF(2 alpha) on Day 18, n = 12). PBLs and plasma were collected on Days 0 (mating day), 15, 18, 19, 20, 21, 23, and 25 by jugular venipuncture. Total RNA was isolated from PBLs. ISGs expression levels were determined by real-time polymerase chain reaction in triplicate. Electrochemiluminescence immunoassay was used to measure progesterone (P-4) levels in plasma. In the ED group, the P-4 level declined to less than 1 ng/mL on Day 19 and remained at a low level until the end of the study. Compared with that on Day 0, receptor transporter protein 4 (RTP4) and ISG15 expression was upregulated on Day 15 and remained high until Day 21 in both groups, and RTP4 and ISG15 mRNA levels were attenuated on Days 23 and 25 only in the ED group (P < 0.001). Myxovirus resistance 1 expression was upregulated on Day 15 and remained high until Day 23 in both groups, but was attenuated on Day 25 in the ED group (P < 0.05). The B2-microglobulin mRNA level did not change significantly during the study in either group. These results indicate that the decline in P-4 concentration was an immediate response to PGF(2 alpha) and that the embryo may have survived longer than the CL on the basis of the extended period of ISGs expression. This suggests that the absence of P-4 could be the reason for ED rather than a direct effect of PGF(2 alpha). In conclusion, the expression of ISGs, including ISG15, RTP4, and myxovirus resistance 1, but not B2-microglobulin, in PBLs may serve as a marker of ED. (C) 2016 Elsevier Inc. All rights reserved.