#10 Immune system and microbiome

Why is it important to care the immune system?

As an owner of six dogs and a veterinary professional for over 12 years, I've come to learn that the immune system is everything! Our medical system, including human medicine, can be quite compartmentalized, but the core issue is the weakened immune system. Our pets and ourselves don't have strong functional systems to protect our bodies, and there are many reasons for that.
How many dogs need to visit for anti-allergy injection? How many cats develop respiratory issues? How many dogs have skin issues?  It's all related to the immune system.
​Because of my love for food medicine, I'd like to explore how the microbiome and immune system are related.

Summaries of studies about the immune system and microbiome

​The interdependence between the microbiome and the immune system is critical for animal health. The microbiota are comprised of billions of microorganisms that live inside and outside the body, shielding it from pathogenic bacteria and stimulating intestinal immune responses. These microorganisms regulate the intestinal environment, neutralizing harmful substances and oxygen tension to prevent invasive bacterial colonization. A healthy immune system depends on this protective mechanism.

Approximately 80% of the body's active B cells are situated in the gut, fighting possible invasion. However, the body must carefully balance inflammation in the intestinal wall to successfully adjust to the scores of microbiota in the gut's ecosystem. Any alteration or imbalance causes dysbiosis, which destabilizes the microbiota, wreaking havoc on immune function and leading to an array of health issues.

Allergies have surged in Western societies, even among pets, due partially to changes in their microbiota. Nutritional values of food also impact and shape the microbiota of pets. The relationship between nutrient metabolism and the immune system is multifaceted, occurring on various levels from hormone signaling to direct nutrient sensing by immune cells. Understanding pets' dietary needs and changes to their diet is crucial to their nutritional well-being.

Microbes communicate with their host's immune system via metabolites, nutrients and other means. This communication is critical to establish functional, innate and adaptive immune responses effectively. Early-life microbial contacts are particularly vital in developing a newborn's immune system. The microbiota generates microbial-associated molecular patterns that aid the immune system's functional development through enterocyte toll-like receptors.

Although dogs and cats have different digestive systems and nutritional requirements, their microbiota's balance is fundamental to their gut's health and, consequently, the immune system. A balanced gut microbiota is particularly vital for the canine gastrointestinal tract, controlled by diet, antibiotics, genetics, management, and environmental factors. The microbiota also varies along the gastrointestinal tract based on nutrient availability and localized microenvironments. Cats require a high protein diet as obligate carnivores, and dysbiosis of their microbiota can cause multiple gastrointestinal disorders. Proper nutrient absorption and digestion are necessary for adequate immune function.

Dysbiosis often causes diseases like canine chronic enteropathy and inflammatory bowel disease, with antibiotics as a common cause. The development of allergies has also been linked to dysbiosis. To uphold optimal animal health, it is crucial to maintain a balanced microbiota, understand the interdependence between the microbiota and immune system, and provide appropriate animal health care.

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References:

Tizard, I. R., & Jones, S. W. (2018). The Microbiota Regulates Immunity and Immunologic Diseases in Dogs and Cats. The Veterinary clinics of North America. Small animal practice, 48(2), 307–322. https://doi.org/10.1016/j.cvsm.2017.10.008
Kau, A. L., Ahern, P. P., Griffin, N. W., Goodman, A. L., & Gordon, J. I. (2011). Human nutrition, the gut microbiome and the immune system. Nature, 474(7351), 327–336. https://doi.org/10.1038/nature10213
Knezevic, J., Starchl, C., Tmava Berisha, A., & Amrein, K. (2020). Thyroid-Gut-Axis: How Does the Microbiota Influence Thyroid Function?. Nutrients, 12(6), 1769. https://doi.org/10.3390/nu12061769
​Marsilio S, Pilla R, Sarawichitr B, et al. Characterization of the fecal microbiome in cats with inflammatory bowel disease or alimentary small cell lymphoma. Scientific Reports. 2019;9(1). doi:https://doi.org/10.1038/s41598-019-55691-w
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