Lead Research Specialist Emory Univ. Sch. of Med., United States
Introduction/Rationale: The Western diet, rich in fats and low in fermentable fibers, has been associated with a range of immune-mediated inflammatory diseases. Dietary fiber is the main energy source for gut bacteria, promoting a rich microbial diversity. We have previously demonstrated that microbiota changes induced by a low-fermentable fiber diet (LFF) impair the development of several intestinal T cell populations. However, the importance of dietary fiber for the intestinal humoral immune system is less understood. Secretory IgA (sIgA) is essential for maintaining gut microbiota homeostasis.
Methods: Here, we show that sIgA is significantly reduced in the small intestinal and fecal contents of mice fed a low fiber diet compared to mice fed a standard chow (SC).
Results: IgA secretion by PC is not impaired, as shown by ELISA of culture media from sorted IgA+ PC from SC and LFF-fed mice. However, flow cytometry and ELISpot assays revealed that low IgA levels are due to a reduction in numbers of small intestinal lamina propria IgA+ PC in LFF-fed mice, while other isotypes are not affected. Using T cell deficient mice, we demonstrate that LFF diet reduces T-dependent, but not T-independent, sIgA.
Conclusion: Future studies will elucidate how changes in the microbiota and dietary fiber result in the loss of IgA+ PCs. To this end, time-stamping of PC will allow to track survival and turnover rate in LFF and control mice. These results provide insight into the interactions between fiber, the microbiota, and B cell responses, and further our understanding on how diet modulates the mucosal immune response.
