Significant neutrophil accumulation, IL-18 deposition, and active inflammasome in tumor regions of human pancreatic ductal adenocarcinoma.

Abstract

e15754 Background: Obesity is an established risk factor for cancer and cancer-related mortality. Adipocytes may act as a “damage” signal resulting in the accumulation of innate immune cells, fueling an inflammatory micro-environment. Among the innate immune cells, tumor-associated neutrophils (TANs) are confirmed to accumulate inside the tumor. As obesity is a significant risk factor for a poorer prognosis in pancreatic ductal adenocarcinoma (PDAC), we hypothesize that obesity-driven adipose fuels the progression of PDAC in a TAN and inflammasome-facilitated manner. This may happen through several mechanisms, including genomic instability of aggressive PDAC clonal populations. Methods: Tissue from resected tumors of PDAC patients with a body-mass index (BMI) > 27 (obesity, n = 5) and BMI < 22 (normal, n = 5) were incubated with anti-human IL-18 and CD66b antibodies and detected using Alexa Fluor 488-conjugated donkey anti–mouse and Alexa Fluor 594-conjugated goat anti-rabbit secondary antibodies. Images were acquired in a Zeiss Axioplan microscope workstation and analyzed by ZEN and Metamorph software. Results: We identified the presence of CD66b+ neutrophils and IL-18 in all tissue sections. There is a significantly greater density of CD66b+ neutrophils and IL-18 in the tumor environment when compared to adjacent normal areas and IL-18+ signals appear to be deposited alongside the luminal area in a unique lasso-like pattern. These data suggest an association between BMI and inflammasome accumulation in the tumor environment. There does not appear to be an association between tumor stage and TAN or IL-18 accumulation in the tumor area or the adjacent normal tissue in the tissues. Conclusions: Our data uniquely shows that CD66b+ neutrophils accumulate inside PDAC and this is associated with intra-tumoral active inflammasomes. The novel periductal deposition of IL-18 in the tumor areas may be of mechanistic relevance in understanding how inflammation induces progression of PDAC. A larger cohort of tissues from PDAC obtained from low and high BMI individuals will be needed to test our hypothesis and to begin to decipher the role of obesity on inflammation and PDAC progression.