The coordinated immune system

The coordinated immune system

Response is the body's sign of defence. It functions by non-specifically dealing with threats without needing to identify them first. 

That makes it a high-performance, quick-acting barrier that can quickly activate the body's natural barriers like skin, tears, and mucus. These first lines of the innate system.

They keep most invaders from ever reaching the body. 

When a microbe or other threat invades the body, they are spotted by patrolling mast cells that can distinguish between foreign proteins. 

These signals trigger local inflammation, increasing blood flow to the site of infection helping to bring white blood cells, such as neutrophils, and carry molecules toxic to bacteria and fungi.

Healthy bone marrow makes about 100 billion new neutrophils, every day, including acinar cells that create highly toxic proteins. Natural killer cells are also made, which destroy infected host cells to limit the spread of infection.

Macrophages are another important immune cell type. They’re nicknamed ‘Pac-Man’ eating anything that they don't recognize as healthy body cells or tissue from cellular cancer cells whose innate immune response usually lasts for only days in length.

The adaptive immune system is one of the most unique and fascinating parts about the immune system. This amazing network has several key features which sets it apart.

First, it has to learn how to respond when you're born. You don't have adaptive immunity for measles or influenza and these other various infections, which means that during your lifetime it learns to respond.

What does it learn?

It learns to bind things very specifically. What we mean by specific, is that the adaptive immune system can tell the difference between two microorganisms which are almost identical and feel out particular components with ease.

That is why the learning process is so important, as you are exploring which organisms pose a danger and these will be the organisms it responds most powerfully to.

The next key feature is that it has what we call a memory, which simply means that your response with a familiar organism will be different from the first time and you're much more likely to avoid infection. And even if you are not protected from reinfection the infection is much less likely severe. 

Here are some of the ways in which this happens and create an understanding of how an adaptive immune response works. 

Our body's white blood cells, called lymphocytes, are really an important component of our adaptive response - in a way being the ‘brains’ of the immune system.

The big question is: how does it do it?

You have a lot of different types of lymphocytes in your body. They can be found all over, but some live only at specific locations such as nodes. The truly unique thing about lymphocytes is that they have a programmable ability to bind with one specific target and each individual lymphocyte can recognise one thing and only one thing.

So then, how does the whole system work? It still sounds a bit mysterious.

What's crucial is your body is full of many different lymphocytes which can all spot different things. 

When you encounter a microorganism, the first part of your adaptive immune response is learning. 

For example, a lymphocyte encounters a virus that it recognises and becomes activated. 

A lot of this activation is controlled by our innate immune system because when we are infected, we have inflammation which helps to identify any bad microorganisms or allergens present in your body.

The activated lymphocyte then goes through a period of extraordinary growth. It replicates, and it replicates and every eight hours you have twice as many of these lymphocytes. So, in only one day your body can generate 10 times more of the lymphocyte than the day before.

Over a period of one to two weeks you can have many millions of lymphocytes, which recognise that specific organism. Whereas when you’ve never encountered the organism before you only had one or two. Due to this you have millions and millions and millions of these cells, you can now start to do something about the infection. When this happens, lymphocytes start to attack and destroy harmful microorganisms. 

This is carried out by antibodies, which are molecules, and are made up by A B lymphocytes, that circulate throughout your bloodstream. It's present in all your tissues, and each individual antibody molecule binds to something very tightly and specifically. This way once you've got millions of lymphocytes, which have recognised a virus or bacterium, the antibody molecules will bind with it, destroying them before they can carry out an array of functions. 

Antibodies work by binding but can also trigger a wide range of different defence mechanisms including triggering the immune system so white blood cells will get rid of any bacteria or virus cells in sight, directly killing bacteria and blocking a virus from ever being able infect other cells in your body.

All of us experience the process of learning, specific binding and then defence mechanisms. It takes a period of time which is why it takes a while before you can be protected by a vaccine or develop recovery from a particular infection. 

So, when we encounter an infection, first of all we have to learn as our lymphocytes get activated. They replicate and grow in number until they form an army capable enough to attack that pathogen.

The other major feature of an adaptive immune response is the ability to remember. 

What happens is that eventually you recover from the infection. Most of your lymphocytes will now fade away because they're not needed at this time but quite a lot are retained, and those are amazing features because these cells can hang around in your body waiting to potentially encounter that microorganism again.

And so, your body then becomes fully defended all throughout your tissues with what are called memory lymphocytes, and those are much more abundant than if you had never encountered that infection before. 

When you recover from a disease or get vaccinated, your body has many millions of these lymphocytes waiting around. Sitting primed and ready, they can defend and kill against incoming infection quickly by rapidly producing antibodies. They're also distributed in the tissues where you might encounter the infection for a second time.

Now you may have heard of another type of lymphocyte called a T-lymphocyte and they work differently but still maintain this critical feature which allows them to recognize very specific microorganisms.

The combination of the mechanism from the antibodies made by B lymphocytes, together with T lymphocytes, makes an extremely powerful system that can recognise infections with exquisite specificity

Some T cells are called killer T cells. 

When a virus gets inside a cell in your body, the best way to get rid of it is to kill the cell which is virally infected, because if you kill the virally infected cells, you will kill the virus. Killer T cells can roam through your body, sniffing out and tasting any evidence that a tissue is infected with the virus. Once they find it then they eliminate that virus infected tissue for good.

Another type of T lymphocyte is called a helper T lymphocytes, helper T lymphocytes protect our body in a range of different ways instead of directly killing.

Helper T lymphocytes can alert a tissue that there's a virus present, and by alerting the tissue this stimulates an inflammatory response that can prevent the virus from replicating in cells. That is one powerful defence against viral infections.

By building a multi-layered structure, we can create an intricate map of the immune system where lots of different components can talk to other components with many, many different signals.

So, the adaptive immune response can learn, has a long memory and it has a very specific way of recognizing bad microbes.

But it's really important to understand that in order to be effective the adaptive immune response must work in cooperation with the innate immune system. 

So, although we talk about innate and adaptive immune systems as being separate components of one much larger whole integrated system - they're both just parts in an even greater mechanism. 

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