Other Experimental Models
Several other models have been developed that seek to address this hypothetical system for immune tolerance, including the depletion of tryptophan via the enzyme indoleamine dioxygenase (IDO) and the expression of the nonclassical MHC class I molecule designated HLA-G. However, genetic deletion of IDO in female mice does not lead to the rejection of their foreign fetal offspring, indicating that a redundant system for the suppression of the mother's immune response exists in the uterus during pregnancy. In addition, HLA-G expresses oligosaccharides that are very different from those linked to other HLA class I molecules, so the possibility exists that HLA-G at the fetomaternal interface is itself employing its unusual carbohydrate sequences as functional groups to suppress the mother's immune response.
Read more about this topic: Eutherian Fetoembryonic Defense System (eu-FEDS) Hypothesis
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