Specific In Situ Detection of Murine Indoleamine 2, 3‐Dioxygenase

Abstract

Indoleamine 2,3-dioxygenase-1 (IDO1) catabolizes the essential amino acid tryptophan, acting as a modifier of inflammation and immune tolerance. Recent work has implicated IDO1 in many human diseases, including in cancer, chronic infection, autoimmune disorders and neurodegenerative disease, stimulating a major surge in preclinical and clinical studies of its pathogenic functions. In the mouse, IDO1 is expressed widely but in situ detection of the enzyme in murine tissues has been unreliable due to the lack of specific antibodies that do not also react with tissues from animals that are genetically deficient in IDO1. Such probes are crucial to establish cellular mechanisms since IDO1 appears to act in different cell types depending on disease context, but reliable probes have been elusive in the field. In this report, we address this issue with the development of IDO1 monoclonal antibody 4B7 which specifically recognizes the murine enzyme in tissue sections, offering a reliable tool for immunohistology in preclinical disease models.

Extensive Profiling of the Expression of the Indoleamine 2,3-Dioxygenase 1 Protein in Normal and Tumoral Human Tissues

“…S2) and of a few blood vessels in the prostate and uterus (data not shown). IDO1 was recently reported to be expressed at high levels in mouse epididymis (36). We observed no staining in human epididymis (Table 1), and we confirmed the lack of expression of the IDO1 gene by RT-qPCR in two human epididymis samples (data not shown).…”

Amino acid auxotrophy as a system of immunological control nodes

“…Therefore, results from the IDO1 or IDO2-deficient mice need to account for the activity of the other protein. Second, commercially available antibody reagents against IDO1 lack specificity 67 (and our unpublished data), and as yet there are no reporter mice that can faithfully track expression of IDO1 or IDO2 in vivo . Finally, the commonly used IDO inhibitor, 1-MT, was shown to be contaminated with tryptophan 68 , or to induce IDO1 69 .…”

Inflammatory Reprogramming with IDO1 Inhibitors: Turning Immunologically Unresponsive ‘Cold’ Tumors ‘Hot’

“…In TDLN from melanoma or breast cancer patients, no difference in the number of IDO1-expressing cells was observed relative to normal nodes [13], in contrast to previous reports [14–17], although evidence of IDO1 activity required for tolerigenic function has been offered [18, 19]. Recently, a knockout-validated, mouse IDO1-specific antibody was reported [20] for murine studies along with Kyn-specific antibodies that may report on IDO/TDO activity [21]. Two caveats here are that nitric oxide produced at tumor sites can inhibit IDO1 activity [22], and Kyn degradation at tumor sites may confound interpretation of IDO/TDO activity.…”