IDO contributes to immune tolerance by regulating tryptophan levels in local microenvironments, such as the tumor microenvironment or sites of chronic infection. By depleting tryptophan, IDO can inhibit T-cell proliferation and promote the differentiation of regulatory T cells (Tregs), which suppress immune responses. This mechanism allows tumors to evade immune surveillance and contributes to the persistence of chronic infections. Understanding how IDO mediates immune tolerance is crucial for developing strategies to modulate immune responses in various diseases.
