Summary Several aspects common to a Western lifestyle, including obesity and decreased physical activity, are known risks for gastrointestinal cancers1. There is substantial evidence suggesting that diet profoundly affects the composition of the intestinal microbiota2. Moreover, there is now unequivocal evidence linking dysbiosis to cancer development3. Yet the mechanisms through which high-fat diet (HFD)-mediated changes in the microbial community impact the severity of tumorigenesis in the gut remain to be determined. Here we demonstrate that HFD promotes tumor progression in the small intestine of genetically susceptible K-rasG12Dint mice independently of obesity. HFD consumption in conjunction with K-Ras mutation mediates a shift in the composition of gut microbiota, which is associated with a decrease in Paneth cell antimicrobial host defense that compromises dendritic cell (DC) recruitment and MHC-II presentation in the gut-associated lymphoid tissues (GALTs). DC recruitment in GALTs can be normalized, and tumor progression attenuated, when K-rasG12Dint mice are supplemented with butyrate. Importantly, Myd88-deficiency blocks tumor progression. Transfer of fecal samples from diseased donors into healthy adult K-rasG12Dint mice is sufficient to transmit disease in the absence of HFD. Furthermore, treatment with antibiotics completely blocks HFD-induced tumor progression suggesting a pivotal role for distinct microbial shifts in aggravating disease. Collectively, these data underscore the importance of the reciprocal interaction between host and environmental factors in selecting microbiota that favor carcinogenesis, and suggest tumorigenesis may be transmissible among genetically predisposed individuals.

BACKGROUND AIMS:: Little is known about the pathogenic mechanisms of autoimmune pancreatitis (AIP), an increasingly recognized, immune-mediated form of chronic pancreatitis. Current treatment options are limited and disease relapse is frequent. We investigated factors that contribute to development of AIP and new therapeutic strategies. METHODS:: We used quantitative PCR, immunohistochemical and ELISA analyses to measure expression of cytokines and chemokines in tissue and serum samples from patients with and without AIP. We created a mouse model of human AIP by overexpressing LT and specifically in acinar cells ( Ela1-LTab mice). RESULTS:: mRNA levels of lymphotoxin (LT) and were increased in pancreatic tissues from patients with AIP, compared with controls, and expression of chemokines ( CXCL13, CCL19, CCL21, CCL1 and BAFF) was increased in pancreatic and serum samples from patients. Upregulation of these factors was not affected by corticosteroid treatment. Acinar-specific overexpression of LT (Ela1-LT) in mice led to an autoimmune disorder with various features of AIP. Chronic inflammation developed only in the pancreas but was sufficient to cause systemic autoimmunity. Acinar-specific overexpression of LT did not cause autoimmunity in mice without lymphocytes(Ela1-LTab/Rag1(-/-)); moreover lack of pro-inflammatory monocytes (Ela1-LTab/Ccr2-/-) failed to prevent AIP but prevented early pancreatic tissue damage. Administration of corticosteroids reduced pancreatitis but did not affect production of autoantibodies, such as anti-pancreatic secretory trypsin inhibitor in Ela1-LTab mice. In contrast, inhibition of LTR signaling reduced chemokine expression, renal immune-complex deposition, and features of AIP in Ela1-LTab mice. CONCLUSIONS:: Overexpression of LT specifically in acinar cells of mice causes features of AIP. Reagents that neutralize LT R ligands might be used to treat patients with AIP.