EFFECT OF IMMUNIZATION AGAINST LEUKEMIA INHIBITORY FACTOR ON THE ESTABLISHMENT OF PREGNANCY IN SHEEP

Leukaemia inhibitory factor (LIF), a pleiotropic cytokine, is implicat ed in blastocyst implantation in mice and maintains the development of ovine embryos in culture. Previously, LIF mRNA and protein were demon strated in the endometrium throughout the oestrous cycle and early pre gnancy in the ewe. In this study pregnant ewes were passively immunise d against human recombinant LIF with polyclonal antibodies raised in c ows by active immunisation. Ewes were immunised during two stages of e arly pregnancy: blastocyst development to hatching, and blastocyst elo ngation to implantation. Only animals passively immunised against LIF showed detectable LIF antibodies in their sera and in uterine lumina f lushings by radioimmunoassay and Western blot analysis. Pregnancy was confirmed by ultrasound on day 55 and a 33.5% non-significant decrease in pregnancy rate of anti-LIF treated animals was observed, when comp ared to animals in control groups (untreated or treated with bovine an ti-keyhole limpet hemocyanin). Cows actively immunised with recombinan t human LIF and exhibiting high levels of LIF antibodies in their sera at the time of blastocyst implantation also showed a reduced pregnanc y rate in comparison to control animals. Although LIF may not be oblig atory for implantation in ruminants it does appear to have a role duri ng the establishment of pregnancy.