IDO1 and infection: In this study, we aimed to characterize the IDO-mediated neutrophil intracellular defense against C. trachomatis because, despite their short half-life, neutrophils can serve as host cells for Chlamydia. Zandbergen et al. showed that infection of human primary neutrophils by C. pneumoniae resulted in a moderate fivefold replication at 90 h post-infection, indicating that the intracellular environment may be permissive for chlamydial survival and a limited degree of growth (24).