Conflicting data has emerged regarding a role for eosinophils in IgA production, with some reports that eosinophils support both secretory and circulating IgA levels during homeostasis. Previous studies have compared antibody levels between wildtype and eosinophil-deficient mice, but these mice were obtained from different commercial vendors and/or were not littermates. Thus, the possibility remains that extrinsic environmental factors, rather than an intrinsic lack of eosinophils, are responsible for the reports of reduced IgA in eosinophil-deficient mice. Here we used wild-type and eosinophil-deficient (dblGATA) mice that were purchased from a single vendor, subsequently bred in-house and either co-housed as adults, co-reared from birth or raised as littermates. We found no differences in the levels of secretory IgA or in the numbers of small intestinal IgA-producing plasma cells between wild-type and dblGATA mice, demonstrating that under controlled steady-state conditions eosinophils are not essential for the maintenance of secretory IgA in the intestinal tract. While we found that levels of IgM and IgE were significantly elevated in the serum of dblGATA mice compared to co-reared or co-housed wild-type mice, no significant differences in these or other circulating antibody isotypes were identified between genotypes in littermate-controlled experiments. Our results demonstrate that eosinophils are not required to maintain secretory or circulating IgA production and the absence of eosinophils does not impact circulating IgG1, IgG2b, IgM, or IgE levels during homeostasis. These findings emphasize the importance of optimally controlling rearing and housing conditions throughout life between mice of different genotypes.

Intestinal helminth infection can impair host resistance to co-infection with enteric bacterial pathogens. However, it is not known whether helminth drug-clearance can restore host resistance to bacterial infection. Using a mouse helminth-Salmonella co-infection system, we show that anthelmintic treatment prior to Salmonella challenge is sufficient to restore host resistance to Salmonella. The presence of the small intestine-dwelling helminth Heligmosomoides polygyrus at the point of Salmonella infection supports the initial establishment of Salmonella in the small intestinal lumen. Interestingly, if helminth drug-clearance is delayed until Salmonella has already established in the small intestinal lumen, anthelmintic treatment does not result in complete clearance of Salmonella. This suggests that while the presence of helminths supports initial Salmonella colonization, helminths are dispensable for Salmonella persistence in the host small intestine. These data contribute to the mechanistic understanding of how an ongoing or prior helminth infection can affect pathogenic bacterial colonization and persistence in the mammalian intestine.

Heligmosomoides polygyrus is a helminth which naturally infects mice and is widely used as a laboratory model of chronic small intestinal helminth infection. While it is known that infection with H. polygyrus alters the composition of the host’s bacterial microbiota, the functional implications of this alteration are unclear. We investigated the impact of H. polygyrus infection on short-chain fatty acid (SCFA) levels in the mouse intestine and sera. We found that helminth infection resulted in significantly upregulated levels of the branched SCFA isovaleric acid, exclusively in the proximal small intestine, which is the site of H. polygyrus colonization. We next set out to test the hypothesis that elevating local levels of isovaleric acid was a strategy used by H. polygyrus to promote its own fitness within the mammalian host. To test this, we supplemented the drinking water of mice with isovalerate during H. polygyrus infection and examined whether this affected helminth fecundity or chronicity. We did not find that isovaleric acid supplementation affected helminth chronicity, however, we found that it did promote helminth fecundity, as measured by helminth egg output in the feces of mice. Through antibiotic-treatment of helminth-infected mice, we found that the bacterial microbiota was required in order to support elevated levels of isovaleric acid in the proximal small intestine during helminth infection. Overall, our data reveal that during H. polygyrus infection there is a microbiota-dependent localized increase in the production of isovaleric acid in the proximal small intestine and this supports helminth fecundity in the murine host.

Background During homeostasis eosinophils are highly abundant in the lamina propria of the small intestine. Eosinophils have been reported to play a role in promoting barrier function in the steady state intestinal tract, and in the control of intestinal colonization by harmless or symbiotic members of the bacterial microbiota. However, the role eosinophils play during enteric infection with a bacterial pathogen is unknown. Aims Our study aims to confirm the previously reported role of eosinophils in supporting intestinal barrier function and to investigate how the absence of eosinophils affects intestinal colonization by an enteric bacterial pathogen. Methods We used wildtype BALB/c and eosinophil-deficient (dblGATA knockout) BALB/c mice that had been cohoused, or bred as littermate controls, to normalize bacterial microbiota populations between mice used for experiments. To investigate steady state barrier function in these mice we used naïve mice to quantify levels of small intestinal IL-1α and IL-1β by cytometric bead arrays, and we used ELISAs to measure levels of immunoglobulin A (sIgA) and serum IgA. Levels of lamina propria-resident B220-IgA+ plasma cells were quantified using flow cytometry. To investigate the contributions of eosinophils to enteric bacterial infection, mice were orally infected with Salmonella enterica serovar Typhimurium. Salmonella burdens along the intestinal tract as well as in the liver and spleen were quantified. Results We found that levels of IL-1α and IL-1β were significantly decreased in the small intestine of naive eosinophil-deficient mice, compared to wildtype mice. In naïve wildtype and eosinophil-deficient littermate control mice, we did not detect any differences in sIgA or serum IgA levels. Additionally, levels of IgA producing plasma cells were similar in the small intestinal lamina propria between wildtype and eosinophil-deficient mice. Following oral Salmonella infection, Salmonella burdens were similar between wildtype and eosinophil-deficient mice both 24 hours and three days post-infection. Conclusions Our data supports a role for eosinophils in modifying steady-state cytokine levels in the intestinal tract. For the first time we report data on IgA levels from littermate controls of wildtype and eosinophil-deficient mice, and contrary to previously published reports, we found that eosinophils are not critical for the maintenance of intestinal sIgA, serum IgA or lamina propria resident IgA producing plasma cells. Our data further concluded that an absence of eosinophils did not impact control of Salmonella infection. Funding Agencies CIHR

Background Chronic infections with intestinal helminths occur primarily in world regions where infections with bacterial pathogens are also common. Research so far has shown that helminths can promote bacterial infection, however, the precise mechanisms of this are unknown. Current helminth control strategies involve mass deworming programs, and it is as yet unclear how deworming impacts susceptibility to bacterial infections in helminth-affected areas. Aims Our aims were to decipher the mechanistic details by which helminths can promote intestinal bacterial infection, and to determine how deworming affects susceptibility to intestinal colonization by bacterial pathogens. Methods Using a mouse model of enteric helminth-bacterial coinfection, we examined how the small intestinal helminth Heligmosomoides polygyrus promotes intestinal colonization by Salmonella enterica serovar Typhimurim. To study the effect of deworming of concurrent Salmonella infection, we treated our helminth-infected mice with the anthelmintic drug Strongid P both before and after Salmonella (co-) infection. To examine whether heightened Salmonella colonization during helminth infection depended on the ability of Salmonella to invade host tissue, we compared the ability of wild-type Salmonella or an invasion-deficient mutant (ΔinvA) to colonize during helminth co-infection. Results An ongoing helminth infection resulted in high levels of Salmonella in the small intestine after co-infection, however, when mice were dewormed prior to Salmonella co-infection, they were no longer susceptible to high small intestinal Salmonella burdens. In contrast, when helminth-infected mice are dewormed after Salmonella has already co-colonized, high Salmonella burdens persisted in the small intestine. Further, we found that during helminth co-infection, Salmonella primarily expands in the gut lumen rather than in the small intestinal tissue, and in line with this, a Salmonella invasion mutant was able to colonize the intestine to a similar extent to wild-type Salmonella during helminth infection. Conclusions Deworming experiments have revealed that the effects of H. polygyrus on promoting Salmonella colonization in the small intestines depend on the ongoing presence of the helminth. Deworming did not revert bacterial burdens once Salmonella had colonized, suggesting that an ongoing helminth infection reduces colonization resistance to Salmonella infection but was not required for Salmonella to persist after initial colonization by Salmonella. Further, we discovered that Salmonella expansion during helminth infection is independent of bacterial invasion of host tissue. Funding Agencies CIHR