IRAK3-mediated suppression of pro-inflammatory MyD88/IRAK signaling affects disease severity in acute pancreatitis

Acute pancreatitis (AP), which is characterized by self-digestion of the pancreas by its own prematurely activated digestive proteases, is a major reason for hospitalization. The autodigestive process causes necrotic cell death of pancreatic acinar cells and the release of damage associated molecular pattern which activate macrophages and drive the secretion of pro-inflammatory cytokines. The MYD88/IRAK signaling pathway plays an important role for the induction of inflammatory responses. Interleukin-1 receptor associated kinase-3 (IRAK3) is a counter-regulator of this pathway. In this study, we investigated the role of MYD88/IRAK using Irak3-/- mice in two experimental animal models of mild and severe AP. IRAK3 is expressed in macrophages as well as pancreatic acinar cells where it restrains NFκB activation. Deletion of IRAK3 enhanced the migration of CCR2⁺ monocytes into the pancreas and triggered a pro-inflammatory type 1 immune response characterized by significantly increased serum levels of TNFα, IL-6, and IL-12p70. Unexpectedly, in a mild AP model this enhanced pro-inflammatory response resulted in decreased pancreatic damage, whereas in a severe AP model, induced by partial pancreatic duct ligation, the increased pro-inflammatory response drives a severe systemic inflammatory response syndrome (SIRS) and is associated with an increased local and systemic damage. Our results indicate that complex immune regulation mechanism control the course of AP, where moderate pro-inflammation not necessarily associates with increased disease severity but also drives tissue regenerative processes through a more effective clearance of necrotic acinar cells. Only when the pro-inflammation exceeds a certain systemic level, it fuels SIRS and increases disease severity.