Three Candidate Probiotic Strains Impact Gut Microbiota and Induce Anergy in Mice with Cow's Milk Allergy.

Cow's milk allergy is a worldwide public health issue, especially since there is no effective treatment, apart from milk and dairy product avoidance. The aim of this study was to assess the beneficial role of three probiotic strains previously selected for their prophylactic properties in a mouse model of ß-lactoglobulin allergy. Administration of Lactobacillus rhamnosus LA305, L. salivarius LA307, or Bifidobacterium longum subsp. infantis LA308 for 3 weeks post-sensitization and challenge modified the composition of the gut microbiota, with an increase in the Prevotella NK3B31 group and a decrease in Marvinbryantia, belonging to the Lachnospiraceae family. Although no impact on markers of sensitization was detected, modifications of foxp3, tgfß, and il10 ileal gene expression, as well as plasma metabolomic alterations in the tryptophan pathway, were observed. Moreover, ex vivo studies showed that all probiotic strains induced significant decreases in cytokine production by ß-lactoglobulin-stimulated splenocytes. Taken together, these results suggest that the three probiotic strains tested lead to alterations in immune responses, i.e., induction of a tolerogenic anergy and anti-inflammatory responses. This anergy could be linked to cecal microbiota modifications, although no impact on fecal short-chain fatty acid (SCFA) concentrations was detected. Anergy could also be linked to a direct impact of probiotic strains on dendritic cells, since costimulatory molecule expression was decreased following coincubation of these strains with bone marrow-derived dendritic cells (BMDCs). To conclude, all three candidate probiotic strains induced strain-specific gut microbiota and metabolic changes, which could potentially be beneficial for general health, as well as anergy, which could contribute to oral tolerance acquisition.IMPORTANCE We showed previously that three probiotic strains, i.e., Lactobacillus rhamnosus LA305, L. salivarius LA307, and Bifidobacterium longum subsp. infantis LA308, exerted different preventive effects in a mouse model of cow's milk allergy. In this study, we evaluated their potential benefits in a curative mouse model of cow's milk allergy. When administered for 3 weeks after the sensitization process and a first allergic reaction, none of the strains modified the levels of sensitization and allergic markers. However, all three strains affected gut bacterium communities and modified immune and inflammatory responses, leading to a tolerogenic profile. Interestingly, all three strains exerted a direct effect on dendritic cells, which are known to play a major role in food sensitization through their potentially tolerogenic properties and anergic responses. Taken together, these data indicate a potentially beneficial role of the probiotic strains tested in this model of cow's milk allergy with regard to tolerance acquisition.

Three Novel Candidate Probiotic Strains with Prophylactic Properties in a Murine Model of Cow's Milk Allergy.

Food allergies can have significant effects on morbidity and on quality of life. Therefore, the development of efficient approaches to reduce the risk of developing food allergies is of considerable interest. The aim of this study was to identify and select probiotic strains with preventive properties against allergies using a combination of in vitro and in vivo approaches. To that end, 31 strains of bifidobacteria and lactic acid bacteria were screened for their immunomodulatory properties in two cellular models, namely, human peripheral blood mononuclear cells (PBMCs) and T helper 2 (Th2)-skewed murine splenocytes. Six strains inducing a high interleukin-10 (IL-10)/IL-12p70 ratio and a low secretion of IL-4 on the two cellular models were selected, and their protective impact was tested in vivo in a murine model of food allergy to ß-lactoglobulin. Three strains showed a protective impact on sensitization, with a decrease in allergen-specific IgE, and on allergy, with a decrease in mast cell degranulation. Analysis of the impact of these three strains on the T helper balance revealed different mechanisms of action. The Lactobacillus salivarius LA307 strain proved to block Th1 and Th2 responses, while the Bifidobacterium longum subsp. infantis LA308 strain induced a pro-Th1 profile and the Lactobacillus rhamnosus LA305 strain induced pro-Th1 and regulatory responses. These results demonstrate that a combination of in vitro and in vivo screening is effective in probiotic strain selection and allowed identification of three novel probiotic strains that are active against sensitization in mice.

Infant gut microbiota is protective against cow's milk allergy in mice despite immature ileal T-cell response.

Faecal microbiota of healthy infant displays a large abundance of Bifidobacterium spp. and Bacteroides spp. Although some studies have reported an association between these two genera and allergy, these findings remain a subject of debate. Using a gnotobiotic mouse model of cow's milk allergy, we investigated the impact of an infant gut microbiota ­ mainly composed of Bifidobacterium and Bacteroides spp. ­ on immune activation and allergic manifestations. The transplanted microbiota failed to restore an ileal T-cell response similar to the one observed in conventional mice. This may be due to the low bacterial translocation into Peyer's patches in gnotobiotic mice. The allergic response was then monitored in germ-free, gnotobiotic, and conventional mice after repeated oral sensitization with whey proteins and cholera toxin. Colonized mice displayed a lower drop of rectal temperature upon oral challenge with b-lactoglobulin, lower plasma mMCP-1, and lower anti-BLG IgG1 than germ-free mice. The foxp3 gene was highly expressed in the ileum of both colonized mice that were protected against allergy. This study is the first demonstration that a transplanted healthy infant microbiota mainly composed of Bifidobacterium and Bacteroides had a protective impact on sensitization and food allergy in mice despite altered T-cell response in the ileum.