The type of immune response during development of acute pancreatitis (AP) determines disease severity. Pancreatic epithelial cells express the interleukin (IL)-22 receptor A1 (IL-22RA1). The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that regulates expression of IL-22. We investigated sources and role of IL-22 in the pancreas, along with the effects of AhR activation on IL-22 expression and AP progression in mice.

We analyzed the effects of recombinant IL-22, a monoclonal antibody against IL-22, and agonists and antagonists of AhR in mice with AP (induced with caerulein or a choline-deficient diet supplemented with DL-ethionine) and control mice. We also analyzed transgenic mice with AhR deficiency (AhR^d and AhR^−/− mice).

CD4⁺ T cells were the main source of IL-22 in pancreatic tissues from healthy mice. During development of AP, numbers of IL-22⁺ CD4⁺ T cells were reduced, whereas IL-22RA1 was up-regulated. Consistent with high levels of IL-22RA1 expression, pancreatic acinar cells responded to IL-22 signaling via signal transducers and activators of transcription 3; administration of IL-22 reduced AP and associated lung injury in mice. AhR was required for production of IL-22 and protected mice from AP. Mice that did not respond to AhR activation developed AP, but administration of IL-22 reduced AP; blockade of IL-22 reversed the ability of activated AhR to protect against AP.

AhR activation protects mice from AP by inducing expression of IL-22. AhR therefore mediates interactions between pancreatic leukocytes and epithelial cells and might be developed as a therapeutic target.