Pregnancy-specific antigens in the sheep: application to the diagnosis of pregnancy

Antisera to 14-day-old sheep embryos were raised in rabbits and used to detect antigens specific to pregnancy by immunofluorescent staining and haemagglutination. Non-specific antibodies were removed by repeated absorptions of the antisera with homogenates of liver and kidney from non-pregnant ewes. The pregnancy-specific antigens were detected using immunofluorescence in the embryo, myometrium, maternal blood and CL as early as Day 8. No fluorescence was detected in pituitary, hypothalamus, liver, kidney, skeletal muscle or endometrium of pregnant ewes, or in any tissues of non-pregnant ewes. Haemagglutination occurred when a 1:8 dilution of rabbit anti-sheep embryo sera was added to blood obtained from ewes between Days 6 and 50 of pregnancy, but not when added to blood from non-pregnant ewes, rams and wethers or from pregnant mares, sows and cows. The immunological activity was removed from the anti-sheep embryo sera by absorption with homogenates of 14-day-old sheep embryo or pregnant uterus, or erythrocytes from Day 14 pregnant ewes, confirming that the antigens were specific to pregnancy. The presence of these antigens provides a basis for a haemagglutination test for pregnancy from Day 6 after mating and may be involved in the maternal recognition of pregnancy in the ewe.