Why is the fetal allograft not rejected?

Area of Science:

• Immunology
• Reproductive Biology
• Genetics

Background:

• Viviparous species require conceptus protection from maternal immune rejection.
• Major histocompatibility complex (MHC) class I proteins are expressed on most somatic cells and can induce immune rejection.
• Trophoblast cells normally downregulate classical MHC class I expression to ensure pregnancy success.

Purpose of the Study:

• To investigate the role of trophoblast MHC class I expression in somatic cell nuclear transfer (SCNT) pregnancies.
• To determine if inappropriate MHC class I expression contributes to high fetal mortality in SCNT pregnancies.
• To explore the potential of MHC class I gene regulation for improving SCNT success rates.

Main Methods:

• Analysis of trophoblast MHC class I antigen expression in normal and SCNT pregnancies at different gestational stages.
• Quantification of uterine stromal lymphocytes in surrogate dams carrying SCNT conceptuses.
• Retrospective study comparing fetal survival rates in SCNT pregnancies using MHC class I-homozygous versus MHC class I-heterozygous cell lines.

Main Results:

• SCNT conceptuses showed premature trophoblast MHC class I expression before day 34 of gestation.
• SCNT pregnancies exhibited increased uterine stromal lymphocytes, indicating an immune response.
• MHC class I-homozygous SCNT pregnancies had significantly higher fetal survival (51%) compared to MHC class I-heterozygous (5%).

Conclusions:

• Inappropriate trophoblast MHC class I expression in SCNT pregnancies likely leads to immune-mediated placental rejection and fetal loss.
• Reduced immunological barriers, achieved through MHC class I homozygosity, improve SCNT fetal survival.
• Precise regulation of MHC class I genes is critical for the immunological acceptance of allogeneic conceptuses in SCNT.