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Much of the body’s immune response depends upon the gastrointestinal microbiome, and understanding its complexities and potential therapeutic targets is essential, particularly in times of stress and/or when risk of infection increases. The composition of the gut microbiota is under the surveillance of the mucosal immune system.¹ Studies suggest that the maintenance of a healthy gut microbiome is inseparable from host health;¹ there is, in fact, a bidirectional relationship between the gastrointestinal microbiome and the innate immune system.² Inflammation, which is caused by abnormal immune responses, influences the balance of the gut microbiome, resulting in intestinal diseases.² Likewise, supporting a balanced intestinal microbial community is essential for the integrity of the immune system, for the prevention and response to infections, and for recovery from illness.^1,2 The microbes and their metabolites influence physiological function (particularly metabolism), local mucosal homeostasis, inflammation, and interactions between multiple body systems.^1,3-5 Therefore, an imbalanced intestinal microbiota may have system-wide effects and contribute to immune health.⁶

 Intestinal homeostasis is maintained by a complex interplay among the epithelium, immune factors, and the microbial flora.⁷ The most recent research identifies cytokines as crucial moderators in the maintenance of intestinal homeostasis. These small proteins secreted in the gut support intestinal homeostasis by governing key cellular processes like cell death, proliferation, molecular transport, and inflammatory responses against pathogens. Cytokines can modulate the division of epithelial cells and assign appropriate immune cells to establish feedback loops.⁷

Changes in the microbial composition induced by diet, alcohol, or antibiotic intake, or due to pre-existing genetic factors, can lead to dysbiosis in the gut and deregulation of cytokine signatures.⁷ Associative links exist in the research between alterations in the microbiome and immune health, as well as some chronic immune/metabolic disorders.⁸ Gut microbiota alterations due to unhealthy lifestyle factors and dietary triggers may contribute not only to inflammation, but also to intestinal permeability; dysbiosis of gut microbiota has been closely linked to several diseases, such as obesity, type 2 diabetes, hypertension, necrotizing enterocolitis, and inflammatory bowel diseases.^1,2Healthy lifestyle factors, including a diversified diet, limited consumption of processed and refined foods, and consumption of adequate dietary fiber, may all promote a healthy microbiome.^1,9 Foods and nutrients that potentially boost immune function also tend to promote gut health. For example, consuming a diverse array of fruits and vegetables rich in antioxidants, anti-inflammatory nutrients, and phytochemicals may reduce oxidative stress, support the liver to promote efficient biotransformation and detoxification, and boost overall immune system function.^10-14 These same fruits and vegetables also contain soluble fibers that “feed” the commensal microbial community in the colon to optimize gut balance and health and insoluble fibers that assist in the efficient processing and elimination of waste from the intestinal tract.¹⁵

References

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2. Shi N, Li N, Duan X, Niu H. Interactions between the gut microbiome and mucosal immune system. Mil Med Res. 2017;4:14. doi:1186/s40779-017-0122-9
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5. Cryan JF, O'Riordan KJ, Cowan CSM, et al. The microbiota-gut-brain axis. Physiol Rev. 2019;99(4):1877?2013. doi:1152/physrev.00018.2018
6. Brzozowski B, Mazur-Bialy A, Pajdo R, et al. Mechanisms by which stress affects the experimental and clinical inflammatory bowel disease (IBD): role of brain-gut axis. Curr Neuropharmacol. 2016;14(8):892-900. doi:2174/1570159x14666160404124127
7. Vahapatro M, Erkert L, Becker C. Cytokine-mediated crosstalk between immune cells and epithelial cells in the gut. Cells. 2021;10(1):111. doi:3390/cells10010111
8. Alemao CA, Budden KF, Gomez HM, et al. Impact of diet and the bacterial microbiome on the mucous barrier and immune disorders. Allergy. 2021;76(3):714-734. doi:1111/all.14548
9. Kashtanova DA, Popenko A, Tkacheva ON, Tyakht AB, Alexeev DG, Boytsov SA. Association between the gut microbiota and diet: fetal life, early childhood, and further life. Nutrition. 2016;32(6):620-627. doi:1016/j.nut.2015.12.037
10.  Hodges RE, Minich DM. Modulation of metabolic detoxification pathways using foods and food-derived components: a scientific review with clinical application. J Nutr Metab. 2015;2015:760689. doi:1155/2015/760689
11.  Jackson SJ, Singletary KW, Murphy LL, Venema RC, Young AJ. Phytonutrients differentially stimulate NAD(P)H:quinone oxidoreductase, inhibit proliferation, and trigger mitotic catastrophe in hepa1c1c7 cells. J Med Food. 2016;19(1):47-53. doi:1089/jmf.2015.0079
12.  Abbaoui B, Lucas CR, Riedl KM, Clinton SK, Mortazavi A. Cruciferous vegetables, isothiocyanates and bladder cancer prevention. Mol Nutr Food Res. 2018;62(18):e1800079. doi:1002/mnfr.201800079
13.  Jiang X, Liu Y, Ma L, et al. Chemopreventive activity of sulforaphane. Drug Des Devel Ther. 2018;12:2905-2913. doi:2147/DDDT.S100534
14.  Minich DM, Brown BI. A review of dietary (phyto)nutrients for glutathione support. Nutrients. 2019;11(9):2073. doi:3390/nu11092073
15.   Holscher HD. Dietary fiber and prebiotics and the gastrointestinal microbiota. Gut Microbes. 2017;8(2):172-184. doi:1080/19490976.2017.1290756