Background & Aims: Acute pancreatitis is a common inflammatory disease mediated by damage to acinar cells and subsequent pancreatic inflammation with recruitment of leukocytes. We investigated the pathologic roles of innate immune cells, especially macrophages, in cerulein and L-arginineinduced acute pancreatitis in mice. Methods: Acute pancreatitis was induced by sequential peritoneal administration of cerulein to mice. We determined serum concentrations of amylase and lipase, pancreatic pathology, and features of infiltrating mononuclear cells. We performed parabiosis surgery to assess the hemodynamics of pancreatic macrophages. Results: Almost all types of immune cells, except for CD11bhighCD11c- cells, were detected in the pancreas of healthy mice. However, activated CD11bhighCD11c - cells, including Gr-1low macrophages and Gr-1 high cells (granulocytes and myeloid-derived suppressor cells), were detected in damaged pancreas after cerulein administration. CCL2-/- mice given cerulein injections developed significantly less severe pancreatitis, with less infiltration of CD11bhighCD11c-Gr-1 low macrophages, but comparable infiltration of myeloid-derived suppressor cells, compared with cerulein-injected wild-type mice. Parabiosis and bone marrow analyses of these mice revealed that the CD11b highCD11c-Gr-1low macrophages had moved out of the bone marrow. Furthermore, mice with macrophage-specific deletion of suppressor of cytokine signaling 3 given injections of cerulein developed less severe pancreatitis and Gr-1low macrophage produced less tumor necrosis factor-α than wild-type mice given cerulein, although the absolute number of CD11bhighCD11c-Gr-1low macrophages was comparable between strains. Induction of acute pancreatitis by L-arginine required induction of macrophage migration by CCL2, via the receptor CCR2. Conclusions: Cerulein induction of pancreatitis in mice involves migration of CD11bhighCD11c-Gr-1low macrophage from the bone marrow (mediated by CCL2 via CCR2) and suppressor of cytokine signaling 3dependent activation of macrophage. These findings might lead to new therapeutic strategies for acute pancreatitis.
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