Used in immunological research to quantify indoleamine 2,3-dioxygenase (IDO) levels in biological samples such as serum, plasma, and cell culture supernatants. IDO is a key enzyme involved in immune regulation, particularly in suppressing T-cell responses and promoting immune tolerance. This ELISA kit enables researchers to study IDO expression in contexts like cancer immunology, autoimmune diseases, pregnancy, and infectious diseases. It is widely used in preclinical studies to evaluate the effectiveness of IDO inhibitors and to understand the role of IDO in tumor immune evasion and inflammatory processes. The assay provides a sensitive and specific means to monitor changes in IDO concentration, supporting biomarker discovery and therapeutic development in immuno-oncology and related fields.