Maternal immunological recognition of pregnancy in equids.

This research article explores the unique occurrence of maternal immune response to pregnancy in species of the genus Equus, particularly in mares. It delves into the fact that mares, unlike most species, generate strong cytotoxic antibody responses toward paternally inherited fetal antigens during pregnancy. The study further investigates the source and impact of these responses on pregnancy.

Immunological Recognition of Pregnancy in Mares

• The research emphasizes that most species don’t show significant evidence of maternal immunological recognition during pregnancy. However, genus Equus members, particularly mares, stand out as an exception.
• During pregnancy, mares produce potent cytotoxic antibody responses against paternally inherited fetal antigens by Day 60 of gestation. The majority of these responses target Major Histocompatibility Complex (MHC) antigens, identified as the primary barrier in successful organ transplantation due to their strong immunogenic nature.

Source of Fetal MHC Antigens

• According to the research, the fetal MHC antigens that trigger the mare’s immune response originate from the specialized trophoblast cells in the chorionic girdle region of the developing placenta.
• These trophoblast cells invade the endometrium between Days 36 and 38 after ovulation, leading to the formation of endometrial cups.
• The precursor girdle cells show high levels of paternal MHC antigens, but the non-invasive trophoblast cells in the allantochorion and the differentiated trophoblast cells in the mature endometrial cups do not. This unique MHC antigen expression by the chorionic girdle cells differs from other types of trophoblast studied in various species.

Impact of Anti-fetal Antibody Responses

• The study finds that these maternal anti-fetal antibody responses in equine pregnancy do not negatively impact fetal development. Moreover, they are not a necessary prerequisite for a successful pregnancy.
• However, the research also suggests that there may be occasional fetal losses due to immunological inconsistencies when the immunoregulatory mechanisms of pregnancy fail.