Bacillus subtilis exopolysaccharide prevents allergic eosinophilia

To the Editor, The composition of the intestinal microbiota has been linked to the risk for developing allergic disease. Although the mechanism by which the microbiota prevents allergic sensitization is unclear, evidence suggests that it is through modulation of the immune system. In this study, we investigated the ability of the spore‐forming gram‐ positive bacterium Bacillus subtilis to prevent the development of allergic disease. Previous work from our laboratory established B. subtilis as an immune suppressive bacterium that can prevent diarrheal disease from Citrobacter rodentium infection. In this study, we tested the ability of B. subtilis spores to prevent house dust mite (HDM)‐induced eosinophilic inflammation using the treatment protocol shown in Figure 1A that was approved by the Midwestern University Institutional Animal Care and Use Committee. C57Bl/6 mice were orally gavaged with 10 WT B. subtilis spores or 10 epsH spores that are unable to produce exopolysaccharide (EPS), due to a mutation in the eps operon. Our previous work found that EPS was the component of B. subtilis required for protection from C. rodentiuminduced inflammation. Following the final HDM treatment, bronchial alveolar lavage was collected from euthanized mice, by flushing the lungs with 0.8 mL PBS (containing 10% FCS, 1 mmol/L EDTA) and immune cell infiltration was assessed by DiffQuik (Dade Behring, Newark, DE, USA) staining of cytospun cells (Figure 1B‐E). HDM from Dermatophagoides pteronyssinus (XPB82D3A2.5; Stallergenes Greer, Boston, MA, USA) alone induces a significant eosinophilia, shown as both percent and total cells per mL (Figure 1B,C). WT B. subtilis spore treatment significantly reduced the eosinophilia in HDM‐treated mice. The B. subtilis-mediated protection was partially dependent on the production of EPS, evidenced by epsH B. subtilis spores being unable to significantly reduce the HDM‐induced eosinophilia.