Metabolism of Tryptophan and Its Role in Immune Tolerance Following Liver Transplantation

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Tryptophan metabolism, particularly via the kynurenine pathway, is crucial for inducing immune tolerance after liver transplantation.
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Indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO2) have distinct, non-redundant roles in liver transplant immunity.
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IDO is primarily expressed in antigen-presenting cells and is induced by inflammatory mediators, while TDO2 is liver-specific and constitutively active.
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Kynurenine, a product of tryptophan catabolism, serves as an endogenous ligand for the aryl hydrocarbon receptor (AhR), influencing immune cell differentiation.
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Current research indicates that combined metabolite panels may provide better insights than single markers in assessing immune tolerance post-transplant.

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