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Fecal Microbiota Of Humans Colonized By Protozoa Regulates The Intestinal Immune Response In Gnotobiotic Mice

The intestinal microbiota plays a fundamental role in the development and regulation of the intestinal immunity. Despite the close interactions between protists and bacteria in the gut, there is little knowledge about the influence of intestinal protozoa over the local balance between intestinal microbiota and immunity.
To know if protozoa-associated human gut microbiota modifies the regulation of the immune response in the gut, a humanized mice model was created by transferring human microbiota into germ-free mice by fecal microbiota transplant from people colonized with multiple intestinal protozoa, such as Entamoeba dispar, Blastocystis hominis, Endolimax nana, Chilomastix mesnili, Iodamoeba butshlii and Entamoeba coli, and from people without intestinal protozoa. Changes on immune regulation were evaluated by measuring intestinal cytokine production, counting lymphocyte populations in colon, and by evaluating the expression of marker genes of intestinal epithelium integrity and mucus production.
The results showed a general downregulation of the immune response in the mice transferred with protozoa-positive fecal samples, characterized by a lower production of pro-inflammatory cytokines such as IFN-g, IL-6 and IL-12, and changes in the architecture of the intestine, such as an increased production of colonic mucus, changes in the gene expression of the tight junction protein tjp1, and in the gene expression of the antimicrobial peptide reg3g.
The protozoa-associated fecal microbiota seems to downregulate the immune response in the gut.