Probiotics – a dietary supplement that may control food allergies                                      

We have always been told the only way to prevent a specific food allergy from happening again is by eliminating that food from our diet! Let’s take a step back to define what food allergy is and why the body is reacting against something that is supposed to be harmless (and tasty). Food allergy is when your immune system unnecessarily reacts against a particular protein in foods. Those proteins are called allergens, and the reaction is an allergic reaction. 

An allergic reaction usually starts with antigen-presenting cells, such as dendritic cells, catching an antigen. It will then present that antigen to its surface so other immune cells can recognize it. When T helper 2 cells acknowledge it, they secrete cytokines such as interleukin 4 and 13. These cytokines will push the B cells to differentiate into plasma cells to release Immunoglobulin E (IgE). The IgE will attach to granulocytes like basophils and mast cells. These cells contain granules that store inflammatory mediators such as histamine. The release of histamine then will cause rashes on the skin, tightening of the respiratory system, and disrupt the gastrointestinal tract, and sometimes, all at the same time. However, the reaction could also be independent of IgE; in that case, it is called a non-IgE-mediated food allergy, during which the allergic person will suffer from vomiting and diarrhea. 

The reason why some people are more prone to adverse reactions to food than others is still a mystery. However, scientists pinpointed that genetic and environmental factors could affect our immune system’s tolerance. 

The digestive tract is one of the most affected organs during an allergic reaction. Thus, the gut needs extra attention. In addition, it is proven that microbiota in the intestine could hold the key to many diseases, including allergies. And as the research on intestinal health expanded, probiotics became popular. Probiotics generally contain living microorganisms that can balance the gut microbiota and regulate the immune system, if administered correctly. 

Based on this concept, researchers examined whether probiotics can help or reduce a condition as chronic as food allergy. Since it has been reported that probiotics can regulate the allergic immune response, Jingyi Ma and colleagues tried to understand the mechanism behind the immune regulation by using induced allergy-like reactions in mice. They utilized the most common allergen in egg white, the ovalbumin protein (OVA), as the inducer.

The researchers first observed that allergy factors and immunoglobulins released by mast cells and plasma cells, respectively, significantly declined on probiotic administration. Another interesting result showed that the intestines of the mice having probiotics+OVA treatment had an accumulation of tolerogenic dendritic cells. These DCs enhanced the differentiation into T regulatory cells and their induction into intestinal tissues such as peyer’s patches and mesenteric lymph nodes. There, T regulatory cells act as a turn-off switch for inflammatory immune cells.

Surprisingly, when they fed the non-allergic mice with probiotics only, they did not observe any changes in the frequency of dendritic cells and T regulatory cells. This suggested that OVA administration may disrupt microbiome homeostasis in the intestine which is in turn affecting the frequency of tolerogenic immune cells. And probiotics by themselves do not affect the microbial composition. In fact, the researchers determined by sequencing that the amount of Falsiporphyromonas, Clostridium XVIII, Staphylococcus, and especially Bacteroides genus increase with OVA-induced allergy but decrease with probiotic administration while Vampirovibrio and Acetatifactor genus behave contrastingly.

We next want to explore if probiotics only affect T regulatory cells, dendritic cells, and microbiota. Or do they influence the intestine membrane as well? The intestinal cells have different types of junctions in between them. Each junction adds to the barrier function of the intestine and regulates the movement of different substances, such as ions, water, and sometimes antigens, which frequently try to cross the intestinal epithelium cells (IECs). 

For that, another study done on mice showed that probiotics tightened these IEC junctions. As a result, it decreases the ability of antigens to cross the barrier and reduces their capability to be presented to immune cells. Furthermore, they saw that probiotics impact the pro-inflammatory signaling of IECs, and as a consequence, lower the inflammation of the intestinal tissues and lead to homeostasis.

To conclude, probiotics could hold great potential, since they significantly decreased food allergies in mice. On the other hand, the clinical study could be complex due to different factors affecting the results, such as the duration of probiotic intake, family genetics, and a significant variation of the microbiome within individuals. Yet, it would be an excellent remedy if something as small and natural as probiotic bacteria could contribute to resolving such a global issue as food allergies. 

Sources:

• Gu, S., Yang, D., Liu, C., & Xue, W. (2023). The role of probiotics in prevention and treatment of food allergy. Food Science and Human Wellness, 12(3), 681-690.
• Ma, J., Zhang, J., Li, Q., Shi, Z., Wu, H., Zhang, H., … & Sun, X. (2019). Oral administration of a mixture of probiotics protects against food allergy via induction of CD103+ dendritic cells and modulates the intestinal microbiota. Journal of Functional Foods, 55, 65-75.

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