Entamoeba nuttalli is an intestinal protozoan with pathogenic potential that can cause amebic liver abscess. It is highly prevalent in wild and captive macaques. Recently, cysts were detected in a caretaker of nonhuman primates in a zoo, indicating that E. nuttalli may be a zoonotic pathogen. Therefore, it is important to evaluate the pathogenicity of E. nuttalli in detail and in comparison with that of E. histolytica. OPEN ACCESS Citation: Guan Y, Feng M, Min X, Zhou H, Fu Y, Tachibana H, et

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... . (2018) Characteristics of inflammatory reactions during development of liver abscess in hamsters inoculated with Entamoeba nuttalli. PLoS Negl Trop Dis 12(2): e0006216. macrophage polarization, there is unambiguous evidence of an intense acute inflammatory reaction in liver of hamsters after infection by both Entamoeba species. Author summary Entamoeba nuttalli is the phylogenetically closest protozoan to Entamoeba histolytica and is highly prevalent in macaques. Previous studies have indicated that E. nuttalli is virulent in a hamster model. In this study, we compared the immunopathological basis of formation of liver abscess in hamsters between E. nuttalli and E. histolytica. Mild liver tissue damage developed after intrahepatic injection of trophozoites of E. nuttalli, and lower expression levels of genes for host proinflammatory factors and amebic virulence proteins were detected at the edges of liver abscesses induced by E. nuttalli. In addition, alternatively activated macrophages were increased in E. nuttalli-induced liver abscesses in the late stage of disease progression. The lysate of E. nuttalli trophozoites also induced higher arginase expression than E. histolytica in vitro. Polarization of macrophages is likely to affect the degree of acute inflammatory reactions in liver in an animal model during E. nuttalli infection. Our data reveal new characteristics of abscess formation by E. nuttalli. Immunopathology of liver abscess by E. nuttalli in hamster PLOS Neglected Tropical Diseases | https://doi. Six-week-old male hamsters were obtained from Shanghai Songlian Experimental Animal Factory. ALA was induced by direct inoculation of 1×10 6 axenic trophozoites of E. histolytica SAW755CR strain or E. nuttalli GY4 strain into liver, as previously described [23]. Pathologic evaluation using liver tissue sections After intrahepatic inoculation of trophozoites, hamsters were euthanized at 3 h, 6 h, 12 h, 24 h, 48 h, 72 h and 168 h post-inoculation. At each time point, 6 to 7 hamsters were used. Liver tissues were harvested and fixed in 4% paraformaldehyde followed by paraffin embedding. Sections were stained with hematoxylin and eosin (HE) or periodic acid-Schiff (PAS) for histopathology [7] . Tissue damage and inflammatory cell infiltration were quantified in high quality images (2560×1920 pixels) captured using a Nikon light microscope. Areas of leukocyte infiltration and liver necrosis were measured using Image-Pro Plus 4.5.1 software (Media Cybernetics). Areas of interest are expressed as a percentage of the total tissue area. Analysis of cytokines by immunohistochemistry and quantitative real-time PCR Immunohistochemical staining was performed as described elsewhere [24]. Briefly, paraformaldehyde-fixed liver sections were deparaffinized, rehydrated by standard protocols and incubated overnight at 4˚C with rabbit anti mouse IFN-γ, TNF-α, IL-1β and IL-6 polyclonal antibodies (Abcam). The slides were subsequently incubated with horseradish peroxidase-Immunopathology of liver abscess by E. nuttalli in hamster PLOS Neglected Tropical Diseases | https://doi.