Your immune response

Your immune response is one of the most important systems in your body – it protects you from invaders and disease.  Your immune response is made up of lots of different parts that work together to keep out microbes or find and destroy any that manage to get through your first line of defence.

The thousands of germs that your body is exposed to every day are often defeated by your body’s first line of defence.  These defences are your external defences and include your skin, the mucus in your ears, nose, throat, lungs and bowels and the acid in your stomach.  Also part of your first line of defence is saliva and the oils and sweat that your skin makes which all have an antibacterial action – they work against bacteria.  Tough defences!  But what happens if microbes get past these defences?  Your second line of defence jumps into action – it is your immune response and it works on the inside.

There are lots of different parts to your immune response including your lymphatic system, your white blood cells and lots of other things.  Your lymphatic system produces lymph, which is a clear fluid that carries white blood cells.  Lymph flows to all the different parts of your body, carrying white blood cell defenders wherever they are needed.  As lymph patrols your body, it finds and picks up any microbes that that have gotten into your body.  These are passed on to your lymph nodes, which are also called your glands.  In your glands, there are special cells that gobble up the microges and destroy them.  These are called phagocytotic cells and are very important defenders.  You have several hundred glands that you can find in your armpits, neck and groin.  If you have an infection, your glands help to gobble up most of the microbes and they also produce antibodies to help destroy them.  You can easily tell if your body is fighting a big invasion – your glands swell up because they are working so hard!

The white blood cells in your blood are the main defenders inside your body – they are cells of your immune response.  White blood cells are also called leukocytes (like our friend Luke O’Cyte).  They find and fight any invaders that manage to get through your first line of defence.  You would have a pretty difficult time staying healthy without your leukocytes! 

Your leukocytes are made in your bone marrow and come in lots of different types.  Some of the most important types are:

• Lymphocytes – these come in two different types; B cells and T cells
• B cells – make antibodies (see below)
• T cells – find invaders that might be hiding in the cells of your body or find cells that are not healthy and destroy them before they make you sick
• Macrophages – these are the biggest blood cells in your body.  They patrol different parts of your body and clean up any invaders or damaged cells they find.  They are phagocytic cells that gobble up and dissolve away the invaders or damaged cells.
• Neutrophils – these patrol your body, finding and destroying invaders.

One type of leukocyte has a job that is vital to your health – your Bcellsmake antibodies.  Antibodies are proteins in your blood that travel around fighting microbes.  Each antibody is unique, it only recognises it’s the one microbe it can fight, but they are really important in keeping you healthy.  When your body sees a microbe for the first time, it does all it can to fight it.  Sometimes you don’t notice that a microbe has invaded, other times you may get a little sick but when you recover, you have antibodies against that microbe in your body.  If that microbe tries to invade your body again, the antibodies are ready and waiting.  They remember how to fight the microbe and quickly destroy it.  Your body will pull out all the stops and will even make more antibodies, all to make sure you don’t feel sick!  Your body is invaded by microbes thousands of times each day but the antibodies of your immune system protect you as much as they can!

If you have antibodies for a particular microbe, it means that you are immune to that microbe and won’t get the disease it causes.  Your body makes antibodies if you have been sick with a disease or if you have been vaccinated.  When you are vaccinated against a particular microbe, the doctor will give you a tiny piece of that microbe that is dead or has had the dangerous part removed so that is safe.  It is enough microbe to make sure your immune system would recognise it if it saw it again, but not so much that you will get sick.  Your body makes antibodies to the vaccine and you are then protected if that microbe ever tries to get past your first line of defence again!

Your immune system is very clever, it know which are the bad cells they should attack and which are good cells they should leave alone.  A perfect example of this are the friendly bacteria like GI Jake that live in your gut, helping to digest your food and keeping you healthy!  These cells live on the surface of your gut and don’t try to invade your cells so your immune system leaves them alone. 

The cells of your body all have a special type of marker that tells your immune system that ‘you’ are you!  You immune system won’t attack your cells because it knows they belong to ‘you’!  When microbes invade or if you have something like an organ donation or skin graft from someone else, your body does not see the markers that say that this is part of ‘you’ and it attacks and destroys the invader.  This is why it can take so long for doctors to find a ‘match’ if they are transplanting an organ or skin.  It can take a very long time to find the very close match that means the immune system won’t destroy the new organ or skin. 

If something goes wrong with your immune system it can lead to a lot of problems.  Your immune system could end up not seeing the markers that say ‘you’ and start attacking your own cells!  Sometimes your immune system can just overreact to harmless things which can lead to allergies to common things like dust or pollen!