Localization of IDO1 in the utero-placental unit leaves us to speculate about its role at this site in particular: IDO1 in the epithelium of the mucosal surface and the glands of the endometrium and the decidua, and secretion of IDO [reflected in Trp-degrading activity in the cervical mucus (26)) may provide a mechanism of innate immunity against ascending infections of the female reproductive tract with intracellular bacteria such as Chlamydia but also against extracellular pathogens. Here, IDO1 is linked to infection.