Microbial symbiosis and immunity

Microbial symbiosis can occur through interactions between hosts and microbial organisms that are beneficial to both parties.^[1] This symbiotic relationship, called mutualism, is constantly taking place throughout a host human or animal's body.^[2] Microflora takes such a large part in supporting the host’s immunity to harmful pathogens, that it becomes vital to the host's health.^[3]

Microbial Symbiosis in the Gastrointestinal Tract

Symbiotic microorganisms, both beneficial and potentially pathogenic, reside in the gastrointestinal tract of humans. Imbalances in the bacterial composition, known as dysbiosis, are thought to be a major determinant in inflammatory bowel diseases such as Crohn's disease in humans. It has long been known that intestinal microorganisms are important for the development of intestinal tissues. A recent study has demonstrated that a human symbiotic microorganism called Bacteroides fragilis protects animals from experimental colitis induced by Helicobacter hepaticus. Polysaccharide A (PSA) from this bacteria singlehandedly protects humans from the inflammatory bowel diseases.^[4]

The gut is home to an extremely complex microbiome of healthy and unhealthy bacteria. The immune system’s primary home is in the gut; so gastrointestinal microbiota has a direct effect on the body’s immune responses.^[5] Without a regular microbiota, the body is more susceptible to infectious and non-infectious diseases.^[6] A great diversity of symbiotic bacteria is necessary for animals to have fundamental nutrients, digest certain compounds, protect against outside pathogens, and create a healthy intestinal structure.^[7] An equilibrium of symbionts and pathobionts is critical to fight off outside pathogens and avoid inflammatory bowel disease. As we understand more about the roles of microbes in the gut, researchers will be able to discover more treatments like probiotics that can fill in niches of good bacteria to increase intestinal health and improve the immune system.^[8] Heightening the robustness and diversity of bacteria flora in the gut aids in averting allergies, autoimmune disease, and cancer.^[9] There is still much to learn about the details of interactions between microbes and hosts in the gastrointestinal tract, but research on symbionts like Lactobacillus reuteri help us understand how changes in the gastrointestinal microbiome can promote health.^[10]

Microbial Symbiosis on the Epidermis

Natural cutaneous microbiota on human skin is vital for the epidermis to fulfill its role as a line of defense against infection. Important microflora that live on the skin, such as Staphylococcus epidermidis produce antimicrobial peptides (AMPs). These AMPs signal immune responses and maintain an inflammatory homeostasis by reducing the release of extra cytokine. Staphylococcus epidermidis and other important microflora work similarly to support homeostasis and general health in areas all over the human body such as the oral cavity, vagina, gastrointestinal tract, and oropharynx.^[11]

References

1. Walter, Jens, Robert A. Britton, and Stefan Roos. "Host-microbial symbiosis in the vertebrate gastrointestinal tract and the Lactobacillus reuteri paradigm." Proceedings of the National Academy of Sciences 108, no. Supplement 1 (2011): 4645-4652.
2. Kitano, Hiroaki, and Kanae Oda. "Robustness trade‐offs and host–microbial symbiosis in the immune system." Molecular systems biology 2, no. 1 (2006).
3. Gallo, Richard L., and Teruaki Nakatsuji. "Microbial symbiosis with the innate immune defense system of the skin." Journal of Investigative Dermatology 131, no. 10 (2011): 1974-1980.
4. A microbial symbiosis factor prevents intestinal inflammatory disease
5. Round, June L., and Sarkis K. Mazmanian. "The gut microbiota shapes intestinal immune system responses during health and disease." Nature Reviews Immunology 9, no. 5 (2009): 313-323.
6. Round, June L., and Sarkis K. Mazmanian. "The gut microbiota shapes intestinal immune responses during health and disease." Nature Reviews Immunology 9, no. 5 (2009): 313-323.
7. Round, June L., and Sarkis K. Mazmanian. "The gut microbiota shapes intestinal immune responses during health and disease." Nature Reviews Immunology 9, no. 5 (2009): 313-323.
8. Hooper, Lora V., Lynn Bry, Per G. Falk, and Jeffrey I. Gordon. "Host–microbial symbiosis in the mammalian intestine: exploring an internal ecosystem." Bioessays 20, no. 4 (1998): 336-343.
9. Kitano, Hiroaki, and Kanae Oda. "Robustness trade‐offs and host–microbial symbiosis in the immune system." Molecular systems biology 2, no. 1 (2006).
10. Walter, Jens, Robert A. Britton, and Stefan Roos. "Host-microbial symbiosis in the vertebrate gastrointestinal tract and the Lactobacillus reuteri paradigm." Proceedings of the National Academy of Sciences 108, no. Supplement 1 (2011): 4645-4652.
11. Gallo, Richard L., and Teruaki Nakatsuji. "Microbial symbiosis with the innate immune defense system of the skin." Journal of Investigative Dermatology 131, no. 10 (2011): 1974-1980.