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An Alliance Between Intestinal Micro-flora And Immunity

Updated on March 17, 2017

Human beings have a mini ecosystem in their bodies, which is constituted by myriads of microflora (also called microbiome or microbiota). Human microflora is made up of communities of symbiotic, commensal and pathogenic bacteria along with fungi and viruses, all of which call our bodies their home. These communities inhabit everything from our skin and genitals, to our mouths and eyes, and, of course, our intestines. Out of them, commensal bacteria have a free ride, whereas the symbiotic bacteria offer a mutually beneficial relationship. Always lurking among them are some disease-causing opportunistic microbes.

The communities in our micro-flora carry out a variety of functions, which are not only vital to our health and well-being but also our very survival.

Intestinal micro-flora –

Bacteria line our intestines and help digest food. During digestion, they make vitamins that are vital for life, send signals to the immune system and make small molecules (metabolites) that can help brain work. Without them, we wouldn’t be anything as they are essential to our health.

The researchers have found that people with certain diseases often have a very different mix of bacteria in their intestines compared to healthier people. It’s not the presence or absence of one particular type of bacteria that makes a flora a healthy one but rather the diversity of bacteria.

In the stomach and small intestine relatively few species of bacteria are generally present. In contrast, the colon contains a densely-populated microbial flora with up to 1012 cells per gram of intestinal content.

The bacterial flora of the small intestine aids in a wide range of intestinal functions. In addition, the large intestine contains the largest bacterial flora in the human body.

Functions of intestinal micro-flora –

They have following key functions:

  • They defend against pathogens, fortifying host defense by its role in developing and maintaining the intestinal epithelium.
  • They induce anti-body production.
  • They metabolize indigestible compounds in foods.
  • They play role in developing immune system.
  • They act as gut-brain axis as biochemical signaling takes place between the gastrointestinal tract and the central nervous system.

Close association between intestinal micro-flora and immunity –

The human gut is home to some 100 trillion bacteria, comprising between 250 and 500 species. This astounding array of organisms is collectively known as gut micro-flora. There exists a close involvement of gut micro-flora and various aspects of health, such as nutritional status, disease behavior and stress response. A presence of pathogenic bacteria requires a well-functioning and strong immune system to prevent infections, which is greatly influenced by the nature and composition of the gut micro-flora.

Probiotics are the groups of naturally occurring microbial species that help perform essential intestinal functions. They have shown their importance and efficacy in controlling a host of immune responses. They do several things that contribute to enhance our immunity.

Common natural probiotics that are present in gastro-intestinal tract are different strains of lactobacilli, bifidobacteria, streptococcus thermophilus, and enterococcus faeceium. Probiotic bacteria develop a mutually advantageous symbiosis within the human gastrointestinal tract. They benefit from the foods we ingest and our bodies utilize the byproducts of their life processes.

They benefit us in the following ways:

  • Probiotics act by promoting non-immunologic gut defense barrier, which includes normalization of altered gut micro-ecology.
  • They also improve intestine’s immunologic barrier, thereby alleviating intestinal inflammatory responses, which produce a gut-stabilizing effect.
  • Many probiotic effects are mediated through immune regulation, particularly through balance control of pro-inflammatory and anti-inflammatory processes. Moreover, distinct regulatory effects have been detected in healthy subjects and in patients with inflammatory diseases.

According to a new study, the researchers have successfully "listened in" on the crosstalk between gut microbes and the immune system. They found that some microbes may up-regulate certain genes to create a more hospitable environment for themselves, while others may down-regulate certain ones to create a more hostile one for harmful bacteria.

When researchers analyzed bacterial effects on genes that regulate the activity of cytokines -- signaling molecules responsible for inducing inflammation in response to infection, cancer and other diseases -- they again found the same balancing dynamics at play viz. some bacteria boosted the activity of these genes while others turned it down.

Summary –

Our bodies have ecosystem of their own, which is essential for their normal functioning. The ecosystem comprises of a number of micro-flora consisting of symbiotic, commensal and pathological bacteria along with fungi and viruses.

Intestinal micro-flora performs a number of functions that are beneficial to us in many ways, one of them being a key role in developing our immunity. Probiotics are naturally occurring microbial species in the gastro-intestinal tract, which help promote our immunity by means of regulating the balance of pro-inflammatory and anti-inflammatory processes.

Reference -

Harvard Medical School. "Scientists monitor crosstalk between intestinal microbes and immune system." ScienceDaily. ScienceDaily, 16 February 2017.

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