Development of models to study Salmonella enterica infection of THP-1 cells pre-treated with IL-27
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IL-27 has been shown to have important pro- and anti-inflammatory roles in the adaptive immune response. However, its role in the innate immune response is less well characterized. The goal of this research was to examine the role of IL-27 in the innate immune response. Two in vitro models of Salmonella enterica serovar Typhimurium infection of the human monocytic cell line, THP-1, were developed. S. typhimurium is an intracellular pathogen that can facilitate its own uptake into host cells where it is able to replicate, often leading to host cell death. Based upon previous research on the role of IL-27 in innate immunity, it was hypothesized that IL-27 pre-treatment of THP-1 cells would result in an enhanced ability of THP-1 cells to fight S. typhimurium infection. Infecting THP-1 cells with late stationary phase S. typhimurium resulted in a low level of infection whereas infection of THP-1 cells with late exponential phase S. typhimurium led to a high level of THP-1 cell infection. Adherent THP-1 cells were stimulated with IL-27 for 16 hours prior to infection with either late stationary or late exponential phase S. typhimurium. A gentamicin protection assay was used to quantify internalized bacteria to assess if IL-27 pre-treatment affected the initial invasion and subsequent survival of S. typhimurium in THP-1 cells. THP-1 cells stimulated with IL-27 had the same level of internalized S. typhimurium as untreated THP-1 cells initially and over the subsequent 12 hours. THP-1 cell viability was monitored between 1-12 hours after the addition of S. typhimurium to determine if IL-27 pre-treatment influenced THP-1 cell death. Pre-treatment with IL-27 did not result in a difference in THP-1 cell death. TNFα and IL-6 secretion from S. typhimurium infected THP1 cells were assayed to determine if IL-27 pre-treatment resulted in an altered cytokine response. IL-27 stimulation resulted in significantly higher (p<0.01) levels of TNFα and IL-6 than untreated cells at 1-12 hours after the addition of S. typhimurium indicating IL-27 stimulation of THP-1 cells promotes a pro-inflammatory response. Overall, IL-27 pre-treatment of THP-1 cells did not alter S. typhimurium infection of THP-1 cells but did enhance the pro-inflammatory response by these cells indicating IL-27 has a role in the pro-inflammatory response by innate immune system to S. typhimurium infection. Further work is needed to explore the host-pathogen interaction that resulted in enhanced cytokine production in THP-1 cells and if this plays a significant role in immune cell survival over an extended time frame. Understanding the role of IL-27 in the innate immune response to pathogens will provide more information on how the immune system combats disease.