SUMMARY Innate lymphoid cells (ILCs) expressing the nuclear receptor RORγt are essential for gut immunity presumably through production of interleukin (IL)-22. The molecular mechanism underlying the development of RORγt+ ILCs is poorly understood. Here, we have shown that the aryl hydrocarbon receptor (Ahr) plays an essential role in RORγt+ ILC maintenance and function. Expression of Ahr in the hematopoietic compartment was important for accumulation of adult but not fetal intestinal RORγt+ ILCs. Without Ahr, RORγt+ ILCs had increased apoptosis and less production of IL-22. RORγt interacted with Ahr and promoted Ahr binding at the Il22 locus. Upon IL-23 stimulation, Ahr-deficient RORγt+ ILCs had reduced IL-22 expression, consistent with downregulation of IL-23R in those cells. Ahr-deficient mice succumbed to Citrobacter rodentium infection, while ectopic expression of IL-22 protected animals from early mortality. Our data uncover a previously unrecognized physiological role for Ahr in promoting innate gut immunity by regulating RORγt+ ILCs.

SUMMARY Aryl hydrocarbon receptor (Ahr) is crucial for the maintenance and function of group 3 innate lymphoid cells (ILCs), which are important in gut immunity. Because Ahr promotes T helper 17 (Th17) cell differentiation in vitro, it is reasonable to expect that Ahr would enhance Th17 cells in vivo. Instead, we show that Ahr deficiency caused increased intestinal Th17 cells, raising the possibility that group 3 ILCs could negatively regulate Th17 cells. Reduced innate interleukin-22 (IL-22) in Ahr-deficient mice allowed expansion of commensal segmented filamentous bacteria (SFB), known to promote Th17 cells. Compared to Rorc+/+Ahr−/− mice, Rorcgfp/+Ahr−/− mice had further reduced group 3 ILCs and were prone to spontaneous colitis with increased SFB and Th17 cells. Innate expression of Ahr played a protective role in T-cell-mediated experimental colitis by suppressing pathogenic Th17 cells. Our data reveal an intricate balance between ILCs and Th17 cells regulated by Ahr and commensal flora.

Intestinal innate lymphoid cells (ILCs) contribute to the protective immunity and homeostasis of the gut, and the microbiota are critically involved in shaping ILC function. However, the role of the gut microbiota in regulating ILC development and maintenance still remains elusive. Here, we identified opposing effects on ILCs by two Helicobacter species, Helicobacter apodemus and Helicobacter typhlonius, isolated from immunocompromised mice. We demonstrated that the introduction of both Helicobacter species activated ILCs and induced gut inflammation; however, these Helicobacter species negatively regulated RORγt+ group 3 ILCs (ILC3s), especially T-bet+ ILC3s, and diminished their proliferative capacity. Thus, these findings underscore a previously unknown dichotomous regulation of ILC3s by Helicobacter species, and may serve as a model for further investigations to elucidate the host–microbe interactions that critically sustain the maintenance of intestinal ILC3s.

Purpose: To provide the first description of a pattern of iron deposition surrounding the hepatic veins in patients with alcoholic cirrhosis and postulate the reason for these findings. Materials and Methods:Two institutions' teaching files were searched for abdominal MRI studies between January 2003 and April 2009 which showed iron deposition within the liver surrounding the hepatic veins. MRI exams were reviewed by two radiologists for iron deposition and signs of portal hypertension. Liver explant pathology reports were also reviewed.Results: Four patients with alcoholic cirrhosis demonstrated perihepatic vein low signal intensity on T1 gradient echo images correlating with iron overload confirmed at histopathologic evaluation of explanted livers.Conclusion: This is the first described uncommon distribution of iron deposition surrounding the hepatic veins. This pattern is well seen on in-phase T1 gradient echo sequences because of the T2* effects in this sequence.