Exogenous stimuli maintain intraepithelial lymphocytes via aryl hydrocarbon receptor activation.

The body's surfaces form the interface with the external environment, protecting the host. These epithelial barriers are also colonized by a controlled diversity of microorganisms, disturbances of which can give rise to disease. Specialized intraepithelial lymphocytes (IELs), which reside at these sites, are important as a first line of defense as well as in epithelial barrier organization and wound repair. We show here that the aryl hydrocarbon receptor (AhR) is a crucial regulator in maintaining IEL numbers in both the skin and the intestine. In the intestine, AhR deficiency or the lack of AhR ligands compromises the maintenance of IELs and the control of the microbial load and composition, resulting in heightened immune activation and increased vulnerability to epithelial damage. AhR activity can be regulated by dietary components, such as those present in cruciferous vegetables, providing a mechanistic link between dietary compounds, the intestinal immune system, and the microbiota.

Mycobacterium gordonae infection in a colony of African clawed frogs (Xenopus tropicalis).

Mycobacterium gordonae is an occasional human pathogen associated with cutaneous infections and nodular granulomatous skin lesions. A case of cutaneous nodular infection caused by M. gordonae in a colony of African clawed frogs (Xenopus tropicalis) is described and confirms this organism to be an opportunistic frog pathogen.