The Mouse Model of Amebic Colitis Reveals Mouse Strain Susceptibility to Infection and Exacerbation of Disease by CD4+ T Cells

Abstract

Amebic colitis is an important worldwide parasitic disease for which there is not a well-established animal model. In this work we show that intracecal inoculation of Entamoeba histolytica trophozoites led to established infection in 60% of C3H mice, while C57BL/6 or BALB/c mice were resistant, including mice genetically deficient for IL-12, IFN-γ, or inducible NO synthase. Infection was a chronic and nonhealing cecitis that pathologically mirrored human disease. Characterization of the inflammation by gene chip analysis revealed abundant mast cell activity. Parasite-specific Ab and cellular proliferative responses were robust and marked by IL-4 and IL-13 production. Depletion of CD4+ cells significantly diminished both parasite burden and inflammation and correlated with decreased IL-4 and IL-13 production and loss of mast cell infiltration. This model reveals important immune factors that influence susceptibility to infection and demonstrates for the first time the pathologic contribution of the host immune response in amebiasis.

Crosstalk at the initial encounter: interplay between host defense and ameba survival strategies

“…Our previous study has reported an increased mast cell infiltration associated with substantially up-regulated mast cell protease genes in infected mouse ceca at 10 weeks post challenge (51). However, the fundamental question that whether mast cells contribute to parasite clearance or play a pathologic role in tissue damage remains unanswered.…”

Resistance of C57BL/6 Mice to Amoebiasis Is Mediated by Nonhemopoietic Cells but Requires Hemopoietic IL-10 Production

“…Indeed, gene expression analysis suggests the absence of a response to amoeba in B6 mice (only 1 of 12,422 genes or expressed sequence tag was dysregulated between B6 sham-and B6 amoeba-challenged mice; data published in (9) and available at ͗https://genes.med.virginia.edu/public data/index.cgi͘). Moreover, B6 resistance does not rely on an innate proinflammatory response in that IL-12p40-deficient, inducible NO synthase-deficient, phagocyte oxidase-deficient, MyD88-deficient, or neutrophil-depleted B6 mice remain resistant (8,9).…”

“…To define the host mechanisms of resistance to intestinal amoebiasis, we have used a mouse model of amoebic colitis that develops upon intracecal inoculation of trophozoites (4,8,9). A majority of CBA or C3H (either TLR4 mutant or wild-type (WT)) 3 mice develop patent infections upon challenge.…”

“…One-half of the cecum was placed in Hollande's fixative, cut into three to five equal cross-sections, paraffin embedded, and 4-m sections were stained with H&E. Histopathology was scored blindly for each mouse as described previously (8). Briefly, numbers of histologically visible amoeba were scored 0 -5 (0, none; 1, present but difficult to locate; 2, occasional, up to 10% of the lumen occupied by ameba; 3, moderate, up to 25% of lumen occupied; 4, heavy, up to 50% of lumen occupied; 5, virtually complete occupation of the lumen by ameba).…”

“…Cecal contents were cultured in trypsin-yeast-iron (TYI-S-33) medium supplemented with 25 U/ml penicillin and 25 mg/ml streptomycin until trophozoite growth was axenic as confirmed by the absence of bacterial growth on Trypticase soy agar with 5% sheep blood (BD Biosciences). For all intracecal inoculations, axenic trophozoites were grown to the log phase and counted with a hemacytometer, and 2 ϫ 10 6 trophozoites in 150 l were injected thrice intracecally after laparotomy as described (8).…”