Are seasonal allergies affecting the quality of your life from March to September?
Allergic diseases have been on the rise over the past couple of decades, but only recently research has been able to identify the cause - our gut microbiota. Gut microbiota are in charge of training our immune system and modulating the immune response, both its innate and adaptive branches. Thus, if you are tired of having to bow to your allergies every summer (or indeed throughout the year), it might be time to look after your microbiome.
The term ‘microbiome' refers to all the microorganisms (bacteria, viruses, yeast, protozoa, etc.) that populate our gut and their respective genes. The actual microorganisms are collectively called ‘microbiota'. It is believed that the number of bacteria in our body are of the same number as the number of all human cells, and there are as many as 1000 bacterial species that populate our gut.
Our gut microbiome is generally formed in the first three years of life. It is highly dynamic and constantly undergoes transformation depending on a variety of environmental factors, such as diet, level of stress, medications we take or any toxins that we are exposed to. Studies on children have shown that treatments by antibiotics in the first year of life negatively impact the diversity of the gut microbiota and lead to a high occurrence of allergic reactions later in life. Having a house pet, such as a dog, in childhood, has been shown to help the enrichment of the gut with the type of bacteria that serve to protect us against later allergies.
Our gut serves two major functions: provide nutrition and the line of defence to our body. Here, the nutrients from the foods we have eaten are absorbed, at the same time a protective barrier in the gut is constantly working as a guard checking for any pathogenic bacteria. Most antigens (foreign invaders such as toxins or viruses) in our gut come from dietary factors, and our gut microorganisms are crucial at modulating our immune tolerance. The immune defence is comprised of the skin, airway and internal defence mechanisms. Multiple studies have shown that gut microorganisms can either promote skin, gut and respiratory system health by strengthening the gut barrier integrity, or on the opposite, they can alter skin integrity and damage the gut and airway protective barrier, with the results of food allergies, atopic dermatitis or asthma.
So what are the mechanisms by which the gut microbiota can either protect us against allergies or on the opposite cause an allergic reaction that nearly always tends to appear ‘out of the blue’?
An allergy is defined as “an overall, systemic immune reaction against a foreign invader, whereas the body’s disease-fighting immune cells misidentify harmless substances as dangerous bacteria or viruses.”
The immune cells attack the allergen trying to expel it from the body. They produce chemicals called IgE antibodies that bind to the allergen, causing the release of histamine, which is responsible for the symptoms of allergies - running nose, wheezing, red or swollen skin, etc.
Our gut bacteria are critical for helping the immune cells to function well and also to mature. When we were children, most of our immune cells matured in the thymus gland (a small organ under the breastbone), which as we grow older becomes less and less involved in the production of immune cells. In adults, immune cells are made in the bone marrow and then migrate to the thymus, the lymph nodes and an area called GALT (gut-associated lymphoid tissue) - just under the surface of the intestinal lining. More than half of the cells that produce antibodies are found here, in the bowel wall. These cells recognise harmful substances, such as pathogens, and mark and destroy them.
The beneficial bacteria in our gut help the immune cells to mature properly because they interact with the cells in our GALT. Research over the past 15 years has shown that our gut contains almost 70% of the entire immune system. So if the good bacteria are not thriving or are outgrown by the ‘bad bacteria’, the production of the immune cells is susceptible to dysfunction.
The families of bacteria in our gut thrive best in balance, where the ‘good bugs’ and the ‘bad bugs’ share the same environment. An imbalance of the bugs, where the amount of healthy bacteria is too low is called dysbiosis.
Dysbiosis can cause a lot of intestinal symptoms, generally diagnosed by a physician as an IBS or IBD (inflammatory bowel disease). The symptoms range from chronic constipation, diarrhoea, gas, bloating, abdominal cramps or nausea after eating, to a general feeling of unwell after eating a meal.
Dysbiosis has a major effect on our immunological tolerance. The specific cells of the immune system - T regulatory cells (Treg) and T helper cells (Th) stop working as necessary and produce an increase in inflammatory agents - cytokines (interleukine 4, IL-4) and antibodies immunoglobulins E (IgE), causing an allergic reaction. So it is the bacterial dysbiosis that is often the cause of a variety of allergic reactions, such as inflammatory disorders of the skin - atopic dermatitis or eczema, psoriasis, and also food allergy, respiratory allergy and asthma.
What can you do if you suffer from an allergy?
Think of your gut as your internal garden, where all the bacteria need to grow with the right amount of good soil, hydration and nutrients. The soil is your intestinal wall, what you have inherited, however, the nutrients are the most important components for the growth of your garden’s plants. Research has demonstrated that our microbiome is very quick to adapt to the changes in our diet, and new families of bacteria start to populate our gut in just two days from changing the diet.
The good bacteria in our gut thrive on the fibre in our diet. They feed on it and grow. The best sources of fibre are vegetables and fruit. Most of the fibre we ingest in not digested by our body, but when it ferments in our gut, families of good bacteria are produced. The best sources of that fibre are green leafy vegetables - broccoli, bok choy, Brussel spouts, rocket, spinach, kale. Eat them raw or grilled, or sauteed in butter - that’s my favourite! But that is an entirely different blog post all together.
Stay healthy! Stay strong!
References:
- Microbiome and Allergic Diseases, “Frontiers in Immunology”, 2018, 9. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6056614/
- Allergy and the Gastrointestinal System, “Clinical and Experimental Immunology”, 2008, 9. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2515351/
- Microbiome and its Impact on Gastrointestinal Atopy, “Allergy’, 2016, 6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976690/
- The Gut Microbiota, environmental factors, the links to the develpment of food allergy, “Clinical and Molecular Allergy”, 2020, 4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7119288/
- Allergy Associations with the Adult Fecal Microbiota: Analysis of the American Gut Project, “EBioMedicine”, 2016, 1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4739432/
- Gut Microbiome as Target for Innovative Strategies Against Food Allergy, “Frontiers of Immunology”, 2019, 2. https://www.frontiersin.org/articles/10.3389/fimmu.2019.00191/full
- Interaction Between the Gut Microbiome and Mucosal Immune System, “Military Medical Research”, 2017, 4. https://mmrjournal.biomedcentral.com/articles/10.1186/s40779-017-0122-9
- The Role of Gut Microbiota in Immune Homeostasis and autoimmunity, “Gut Microbes”, 2012, 1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3337124/
