Role of Gut Microbiome in Allergy Development
In the last blog, we discussed the central role of gut microbiome and how it plays an integral role in determining your well-being — through a complex interplay that includes the immune system as well as a host of physiological activities and responses.
Let us understand what research tells us about the role of gut microbiome in allergy development.
But first, a quick recap.
What is an allergy? (or at least what we know about it!)
Allergy occurs when there is a problem with the immune system. We know that the immune system keeps us safe from diseases. It protects our body from internal and external threats. And it is an extremely powerful system capable of hurting you very badly. So it makes sense not to rub this chained beast the wrong way.
The immune system knows how to distinguish between self and non-self — something that is part of your body, and something that is foreign. When it encounters anything foreign, it may deem it to be harmful to the body and gives an appropriate response. If it is a harmful, disease-causing bacteria, it will give a response that results in the destruction of the bacteria, before it can cause a severe infection.
An immune response does result in some tissue damage — a small price we pay for overall protection. Unfortunately, there are times when our immune system gives a disproportionate response to a seemingly innocuous foreign particle, say a pollen grain. Under no circumstances is the pollen grain capable of causing any harm to our body. But if the immune system thinks otherwise, it mounts a response that does more harm than good. Being sensitive to foreign particles is good; the problem is when the immune system becomes “hypersensitive.” In an effort to “clear” the supposed harmful foreign particle (the harmless pollen), our immune system mounts a response that leads to widespread tissue damage, along with a host of other problems. In some cases, such a response can actually lead to death.
This condition is called “hypersensitivity” and allergies are classified as Type 1 hypersensitivities. Let’s not go into the other three types as the area of our interest has already been mentioned.
How is gut microbiota related to allergy?
Okay, let us understand certain things. Just because everything is genetically controlled, doesn’t mean that if you or I have a gene that makes us prone to something, it will happen to us. There is something called “epigenetics” — the science of the impact of our environment on our genes. But that is for another time.
If an individual is genetically predisposed to allergy, she is called “atopic.” Whether this atopy will manifest as an allergy depends on many factors.
Consider this. A set of twins are atopic. Let us assume that they may develop an allergy towards ‘Allergen Z’. Immediately after birth the twins are separated geographically; one (A) is carried all the way to live on an Antarctic station, while the other (B) stayed at the place of her birth. While both the siblings are genetically similar, B will encounter Allergen Z and has more chances of her atopic condition manifesting as an allergy. Sibling A, on the other hand, never comes across Allergen Z throughout her life and so she may never develop the allergy.
In the above scenario, we have assumed the absence or presence of the allergen in the environment as a factor in the development of the allergy. But even if the allergen is always present in the environment, there are many factors that will determine whether an allergy will develop or not.
In this light, it has been examined that the gut microbiota composition during the first months of life influences allergy development, and supports the theory that factors influencing the early maturation of the immune system might be important for subsequent allergic disease.
In a research study, scientists performed a retrospective study on children in two countries — Sweden and Estonia. They concluded that “differences in the composition of the gut flora between infants who will and … will not develop allergy are demonstrable before the development of any clinical manifestations…, we believe that our findings could indicate a role for the intestinal microflora in the development of and protection from allergy.”
Scientists have also demonstrated, for instance, that a low gut microbial diversity during the first month of life precedes the development of atopic eczema and asthma in children at 2 and 7 years of age, respectively.
Whether a child is born naturally (vaginal delivery) or through a Caesarean section (C-section) has a great impact on composition of the child’s gut microbiota. This in turn makes the child vulnerable to many health issues in the future. One of them is allergy.
Another interesting fact associated with the development of a healthy, symbiotic gut microflora in the child is the mother’s nutrition and her own gut microbiome during pregnancy and post-delivery, when she is breast feeding the child.
In the last blog, we talked about the “Hygiene Hypothesis” and how the enhanced levels of cleanliness are one of the reasons for rise in autoimmune disorders (AD). It is clear that if the immune system (as it is evolving in a growing child) doesn’t receive enough challenges during the course of time, it is likely to malfunction and this may manifest as an AD or any other chronic disorder.
Parting thoughts
The gut microflora, as we have seen, plays a vital role in modulating the immune system. A healthy, balanced gut flora is of prime importance in maintaining a well-functioning immune system. If the gut flora is not balanced, or is qualitatively inferior, it may fail in its primary function of keeping the immune system healthy. This, in turn, may result in allergy manifestations in atopic individuals.
The rapid rise in allergy cases in the last couple of decades makes us realize that our changing lifestyles are responsible for drastic changes in our gut microbiota diversity, making us vulnerable to a host of chronic disorders, including autoimmunity and allergies.
In the next article, we shall discuss how gut flora helps keep our immune system and that we are harboring a very powerful, and potentially dangerous system that has the ability to (literally) kill us, if its awesome powers go awry.
Till then, stay tuned.
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