Because foetuses contain 'foreign' paternal proteins, they must be protected from destruction by maternal T cells during pregnancy. An enzyme called indoleamine 2,3 dioxygenase (IDO) is involved in this natural immune tolerance but it is not known what exactly the IDO enzyme does.

In research published in the January Nature Immunology, Andrew Mellor and colleagues from the Medical College of Georgia, US found that in pregnant female mice treated with an IDO inhibitor, the T cells cause complement deposition and hemorrhagic necrosis at the maternal–foetal interface, leading to foetal death (Nature Immunol 2001, 2:64-68).

If it turns out that some cases of recurrent abortion in humans are due to insufficient IDO, treatment with IDO might help the mother to tolerate the foetus. IDO might even be used to suppress immunity in transplant patients.

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