The Intersection of Immune Responses, Microbiota and Pathogenesis in Giardiasis

Abstract

Abstract Infection with the protozoan parasite, Giardia, can produce a range of symptoms including diarrhea, severe cramps, and nutrient malabsorption. Our lab and others have previously indicated that immune responses can contribute to pathogenesis. It has also been reported that intestinal microbiota can affect the ability of the parasite to colonize laboratory mice. Our goal was to determine if intestinal immune cells were activated following infection and how the microbiota interacted with intestinal immune responses. Wild-type or CCR2 deficient mice were treated with a cocktail of antibiotics and infected with the GS strain. Control mice were not treated with antibiotics and/or were not infected. Changes in the intestinal microbiome and immune responses were determined using 16S sequencing and flow cytometry of isolated lamina propria and intraepithelial lymphocyte populations, respectively. Sucrase activity was also measured in mucosal lysates. Mice treated with antibiotics or infected with Giardia exhibited shifts in their intestinal microbiomes. With or without antibiotics, we observed an increase in the frequency of CD4+ T cells in the lamina propria at day 7 post-infection. We also observed an increase in macrophage populations and activated CD8+ T cells, but only in mice not treated with antibiotics. Macrophage populations increased in wild-type and CCR2-deficient mice, and EdU labeling suggested in situ proliferation of resident macrophages. Finally, sucrase deficiency correlated with activation of CD8+ T cells. Together these data indicate that the intestinal microbiota contribute to immune cell activation during infections and suggest that the microbiota may contribute to different infection outcomes.