8 February 2016

Our microbiota helps us fight colds

Our immune system is a fantastic well-oiled machinery where each component has a defined role. If we remember our Biology classes, there are two main types of immunity: a non-specific one (the innate) and a specific one (the adaptive, capable of learning baddies’ attacks and remembering how to fight them off).

All these immunity (police) agents have elected certain sites such as the skin, the intestines and the appendix as their home because their biggest job is to keep our residing micro-organisms under control. It is not surprising then that they ended up interacting, right?

In fact, it is our own police agents who decide that it would be OK to accept those microbes to populate our body, right from birth:
When a baby gets born, his skin, body, or gut doesn’t contain any microbes (although this is now a debatable matter, more on this later). As soon as baby is out through the birth canal or through his mum’s belly, baby picks up microbes. But bizarrely, he’s fine with it, he doesn't get sick. The reason for this acceptance is that a growing baby’s immune system is purposefully down to accept the little bugs, knowing that they will be useful later on.

baby

From this, we can already wonder if there is a difference then between being born naturally and being born by C-section. This is a very interesting point and I’m planning on addressing it very soon in another article.

For now, let’s come back to our gut immune cells and microbes working together to fight off illnesses:

The way it works is complex. But let’s imagine a virus trying to infect us. Infection intensity will depend on 1. how well we are physically, 2. what our genetics say, and 3. where the virus is attacking. This viral invasion triggers highly specialized populations of cells to collect cues from right, left and centre in order to develop responses that will allow to fight the virus.

It was recently discovered that when our gut bacteria break down the fibres from our food, they produce short chains fatty acids, SCFA. These amazing SCFA were shown to regulate the part of our immune system that modulates our human genes. This in turn results in a positive effect on essential components of our adaptive immune system (T cells and dendritic cells) that will fight the invasion for us (I will be exploring the impact of low fibre diet very soon).

NK cell attacking a cancer cell
Two immune cells attacking a cancer cell

The innate immune system also can be modulated by our gut bacteria, fungi or viruses that all live and act for everyone’s sake:

Indeed the reason why our tiny allies are fighting for us is also to defend their home by stopping the bad invaders to colonise their territories. They do so by forbidding the virus to eat on site, or by creating a difficult place to live in (acidic environment, production of natural killing juice).

Most of our immune cells reside where our friendly bacteria are, for a mutual protective role – Do you want to tweet this?

Clever little buggers, aren’t they? Bu then again, they have been existing for far longer than us…

Do you remember the basics in immunity we used to learn at school? Do you think next generations will or should study this as part of their normal curriculum?

I based my article on the review by Belkaid Y and Hand TW, 2014 that was published in Cell, a highly reputable scientific journal.

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My bugs and I Published @ 2014 by Ipietoon