Do you ever think about all those minute micro-organisms that are dwelling in your body? 

After having looked at the role of genetics in immunity and whether adaptogens can have an effect on the immune system, we turn to gut microbiota and how it influences the immune system. 

Let’s start with the basics.

What is the microbiome?

The microbiota living in our body comprises of several microbes, which include bacteria, fungi, protozoa, helminths and viruses; the genes they collectively encode is identified as our microbiome (1). 

Believe it or not, these very microbes in our gut help regulate the immune system – they fight microbes from the outside. This is why it’s necessary for us to learn why gut microbes are so important.

The human microbiome is a complex and important subject and it has an effect on our health and well-being. Tremendous work on this is underway in the biomedical research space, and most of the research work being done is on the gut microbiome(2). The composition of the human microbiome depends on genetic, immunological and environmental (including diet and environmental biodiversity) factors.  

Why the emphasis on gut microbes?

The human gut is the place with the highest concentration of immune cells and microbiota (bacteria) and, therefore, it is a major site for learning about the immune system(3). Studying it thoroughly can help us prevent immune disorders. 

Immunity is the ability of our body to fight against, or get rid of, foreign organisms or abnormal cells or substances that have the potential to cause harm to us, while the immune system is the entire network of cells, tissues that works together to successfully do this. 

Coming back to the question at hand – what’s the connection between the overall immune system and gut health?

How are microbiome and the immune system related?

Microbiome and the immune system are intertwined and these two systems are continuously influencing each other(2). Research shows that microbiome is linked to both innate and adaptive immunity and, to a certain extent, influences the optimal functioning of the immune system(5). The bacteria of the gut influence the development of the immune system, especially the adaptive immune system. 

The interaction between the host immune system and microbiota may be symbiotic or pathogenic, and takes place mostly in the gastrointestinal system(6). One of the major functions of the immune system is to control our relationship with the microbiota. 

Let’s understand this connection better by learning how the immune system of a newborn develops. Initially, the immune system of the baby is not totally functional yet, making infants very susceptible to infections. The colonisation of the microbiota in the gut of a baby starts around the time of birth (from micro-organisms from mother), during delivery and after birth (micro-organisms from the environment). It starts maturing with age and as the infant is exposed to different environmental factors(3). One of the key factors is the commensal microbiota present in the body of the infant. The immune system, in turn, has an effect on the composition of the microbiota.

The symbiotic bacteria in our body seems to have developed means and methods through which it protects us from pathogenic microorganisms. If there are lowered levels of symbiotic organisms and their beneficial molecules, it may lead to disease(6). Health issues such as allergies, autoimmune and inflammatory disorders occur because of uncontrolled immune response against the self, microbiota or environmental antigens(5).

Simply put-

A large part of our immune system has evolved in the process of maintaining a symbiotic connection with the highly complex and diverse groups of microbes in the body. The microbial population helps to stimulate, and also regulate, the various facets of our immune system. 

In other words, we can say that our complex immune system is dependent on the microbiota residing in our body.

What happens when the microbiome equilibrium is disturbed?

If, for any reason, the microbiome equilibrium is disturbed, it affects the immune system response of the host. If the defence system of the host is disrupted, it leads to the development of disease, the treatment of which may affect the microbiome. This demonstrates how the pathways of microbiota and immune system are strongly interwoven(2).

What is the role of probiotics and prebiotics in influencing gut microbiome? 

Probiotics are beneficial bacterial species such as mainly Lactobacilli and Bifidobacteria, which are thought to promote health. A prebiotic is a non-digestible food ingredient which favourably affects host health by selectively encouraging the growth and activity of bacteria in the large intestine. 

Prebiotics are a group of nutrients such as fructo-oligosaccharides and galacto-oligosaccharides that are degraded by gut microbiota(7). They are present in foods like wheat, onion, banana, garlic and chicory(8). 

Probiotics and prebiotics together influence the composition and growth of beneficial bacteria in the gut. They help in the maintenance of the microbiome equilibrium, and hence have an effect on the immune system too.

It is extremely important to pay attention to what one eats so that the diet promotes the growth of beneficial bacteria in the gut, which will then boost immune system too. We have also explored the role of antioxidants in improving immunity here.  In the end, it looks like the intricate and multifaceted defence system constructed by our body against microbes is, itself, regulated by the microbes in our body(6). Understanding how the microbiome and immune system work in relation to each other can help us prevent infections and allergies. Here are other measures to boost immune system.