Abstract
The microbes in the gastrointestinal tract are separated from the host by a single layer of intestinal epithelial cells (IECs) that plays pivotal roles in maintaining homeostasis by absorbing nutrients and providing a physical and immunological barrier to potential pathogens. Preservation of homeostasis requires the crosstalk between the epithelium and the microbial environment. One epithelial-driven innate immune mechanism that participates in host-microbe communication involves the release of reactive oxygen species (ROS), such as hydrogen peroxide (H
2
O
2
), toward the lumen. Phagocytes produce high amounts of ROS which is critical for microbicidal functions; the functional contribution of epithelial ROS, however, has been hindered by the lack of methodologies to reliably quantify extracellular release of ROS. Here, we used a modified Amplex Red assay to investigate the inflammatory and microbial regulation of IEC-generated H
2
O
2
and the potential role of Duox2, a NADPH oxidase that is an important source of H
2
O
2
. We found that colonoids respond to interferon-γ and flagellin by enhancing production of H
2
O
2
in a Duox2-mediated fashion. To extend these findings, we analyzed
ex vivo
production of H
2
O
2
by IECs after acute and chronic inflammation, as well as after exposure to dysbiotic microbiota. While acute inflammation did not induce a significant increase in epithelial-driven H
2
O
2
, chronic inflammation caused IECs to release higher levels of H
2
O
2
. Furthermore, colonization of germ-free mice with dysbiotic microbiota from mice or patients with IBD resulted in increased H
2
O
2
production compared with healthy controls. Collectively, these data suggest that IECs are capable of H
2
O
2
production during chronic inflammation and dysbiotic states. Our results provide insight into luminal production of H
2
O
2
by IECs as a read-out of innate defense by the mucosa.
