Context is key: Maternal immune responses to pig allogeneic embryos

Abstract

Successful establishment of pregnancy includes the achievement of a state of immune tolerance toward the embryos (and placenta), where the well-coordinated maternal immune system is capable of recognizing conceptus antigens while maintaining maternal defense against pathogens. In physiological pregnancies, following natural mating or artificial insemination (AI), the maternal immune system is exposed to the presence of hemi-allogeneic embryos, that is, embryos containing maternal self-antigens and foreign antigens from the paternal side. In this scenario, the hemi-allogeneic embryo is recognized by the mother, but the immune system is locally modified to facilitate embryo implantation and pregnancy progression. Pig allogeneic pregnancies (with embryos containing both paternal and maternal material foreign to the recipient female), occur during embryo transfer (ET), with conspicuously high rates of embryonic death. Mortality mainly occurs during the peri-attachment phase, suggesting that immune responses to allogeneic embryos are more complex and less efficient, hindering the conceptuses to survive to term.Reaching a similar maternal tolerance as in conventional breeding would render ET successful. The present review critically summarizes mechanisms of maternal immune recognition of pregnancy and factors associated with impaired maternal immune response to the presence of allogeneic embryos in the porcine species.

Mating modifies the expression of crucial oxidative-reductive transcripts in the pig oviductal sperm reservoir: is the female ensuring sperm survival?

“…Certainly, semen was signaling to the female to activate its local immune system to counteract incoming micro-organisms, cells, and proteins from damaging effects ( 7 ). The female, nevertheless, tolerates a certain proportion of spermatozoa, those colonizing the UTJ-reservoir and further on the hemi-allogeneic embryos and their placentas, for the entire pregnancy ( 37 ). Estrogens, particularly oestradiol, exert clear effects on the immune system during this particular period ( 38 ) as well as on the genital tract epithelia ( 39 ) and the spermatozoa, cells provided with, among others, estrogen receptors ( 40 – 42 ).…”