Administration of thymocytes derived from nonpregnant mice induces an endometrial receptive stage and leukaemia inhibitory factor expression in the uterus

We have previously reported that intravenous administration of splenocytes prepared from mice in the early stages of pregnancy promoted embryo implant ation in pseudopregnant mice, Since a T-lymphocyte-rich, but not a monocyte -rich preparation from splenocytes enhanced embryo implantation, similar ef fects of thymocytes from non-pregnant mice on implantation were examined in this study, Thymocytes were prepared from immature 21 day old ICR female m ice and the supernatant of a thymocyte suspension (Th-sup) was used as the control, Thymocytes or Th-sup were injected into the caudal vein of recipie nt mice on pseudopregnancy day 2, and blastocysts were transferred into the endometrial lumen. The implantation rates per recipient were significantly higher in the thymocyte-treated group. ICR mice were then oophorectomized on pseudopregnancy day 3, After 3-day progesterone supplementation, blastoc ysts mere transferred with intravenous injection of thymocytes or Th-sup. U nder progesterone supplementation, successful implantations were observed i n the thymocyte-treated group, but not in the Th-sup-treated group. Reverse transcriptase-polymerase chain reaction analysis revealed that mRNA expres sion of leukaemia inhibitory factor in the uterus was induced by thymocyte administration, but not by Th-sup, Thymocytes mere divided into two populat ions, CD4(+/-)CD8(-) group and CD4(-)CD8(+/-) group, by separation columns. On pseudopregnancy day 2, the separated thymocytes in each group or their supernatant mere injected into the endometrial stroma of the recipient mice , and blastocysts were transferred into the endometriaI lumen, The administ ration of CD4(+/-) CD8(-) lymphocytes significantly promoted implantation r ates, but no effect was observed in the CD4(-) CD8(+/-) group, These findin gs showed that thymocytes, especially CD4-positive lymphocytes, facilitate embryo implantation, probably by regulating endometrial differentiation.