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

Overview

This review discusses the role of tryptophan metabolism in immune tolerance after liver transplantation, focusing on the functions of indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO2).

Background

Liver transplantation is essential for patients with end-stage liver disease, yet long-term outcomes are often compromised by complications from immunosuppression. Understanding the mechanisms of immune tolerance is crucial. Tryptophan metabolism, particularly through the kynurenine pathway, is a factor in regulating immune responses in the liver.

Data Highlights

No numerical data or trial data presented in the article.

Key Findings

• Tryptophan metabolism is regulated by IDO and TDO2, with IDO being inducible by pro-inflammatory mediators.
• The serum kynurenine/tryptophan (Kyn/Trp) ratio serves as a biomarker for IDO activity.
• IDO upregulation correlates with spontaneous graft tolerance in preclinical models.
• Overexpression of IDO may not always confer protection against rejection.
• Microbiota-mediated indole metabolism is involved in the gut-liver axis.

Clinical Implications

Further research is needed to explore the role of tryptophan metabolism in immune tolerance in liver transplantation.

Conclusion

Tryptophan metabolism is an area of research for immune tolerance in liver transplantation, but it remains largely in the preclinical stage.

Related Resources & Content

1. The Journal of Infectious Diseases, 2023 -- Exploring Tryptophan Metabolism as a Focus for Tuberculosis Biomarkers and Host-Directed Therapeutic Approaches
2. Frontiers in Immunology, 2026 -- CD8 regulatory T cells are a novel type regulatory T cells in the induction of transplantation immune tolerance
3. Frontiers in Immunology, 2026 -- Immunosuppression after pediatric liver transplantation may lead to early and prolonged acute thymic involution: findings from a pilot longitudinal study
4. EASL Clinical Practice Guidelines, 2024 -- Liver Transplantation
5. AASLD AST Practice Guideline, 2025 -- Diagnosis and management of graft-related complications
6. Frontiers in Immunology — Immunopathogenesis of Antibody-Mediated Rejection in Liver Transplantation
7. EASL Clinical Practice Guidelines
8. AASLD AST Practice Guideline
9. Scientific summary - The clinical utility and safety of biomarker-guided immunosuppression withdrawal in liver transplantation: the LIFT prospective RCT - NCBI Bookshelf
10. Donor-specific immune senescence as a candidate biomarker of operational tolerance following liver transplantation in adults: Results of a prospective, multicenter cohort study - PubMed
11. Plasma microRNAs and chemokines as biomarkers for rejection in liver transplantation with score verification and tissue correlation | Scientific Reports
12. Frontiers | Contribution of tryptophan and its metabolites to transplant outcome: a mini-review