What is your immune system?
Your body’s immune system is the complex system of cells and organs which gives you protection against infection and illness. You can see some of it, for example your skin, tears, and mucus. But there’s much more if it you can’t see, including specialist blood cells and bone marrow.
Your immune system knows which cells are part of your body and recognises anything unfamiliar which poses a threat. Its job is to get rid of any outside attacks before you can get ill.
The first line of defence
The front line of your immune system tries to stop bad microbes from getting inside your body in the first place. These are the bits of your immune system you can see or feel: your skin, mucus membranes, tears, saliva, and blood clots. It also includes the normal body flora in the lining of your nose and digestive system.
Did you know that the human gut contains around 1kg of good bacteria?
The second line of defence
If an invading infection manages to get past all that, your immune system activates the next stage of protection. This includes phagocytes (a type of white blood cell).
How does your immune system recognise your own cells?
It’s pretty amazing, really! Your body’s cells all have a kind of ID-tag on them called antigens. Antigens identify your own cells as a natural part of your body. By reading this tag, your immune system knows these cells are yours and belong in your body. If a virus, germ, or bacteria tries to get into your body, your immune system will know it is an invader because of the strange antigens.
Did you know that your antigens are unique to you, unless you are one of a pair of identical twins?
What your immune systems guards against
Your immune system will do its best to protect you against anything unfamiliar. This includes infections, bacteria, and parasites. Virus particles are tiny and can enter healthy cells. Bacteria are larger than viruses, but still small enough to invade our cells. Some bacteria are useful and necessary like the gut bacteria that helps us digest our food.
Your immune system works hard to know the difference and get rid of the dangerous type but it can also backfire by being a little over enthusiastic! It can over react to harmless external invaders (which is what happens when you have hay fever) or it can attack donated blood cells or organs from a donor. Sometimes, a person’s immune system can turn against the body’s own cells- this is called autoimmune disease.
1000 million defender cells
Your immune system really is incredible. It uses a huge army of white blood cells (called defender cells) to fight off infection and bacteria. Your body makes about 1000 million defender cells every day in your bone marrow. Defender cells include macrophages which circulate around your body constantly looking out for foreign invaders. This is the natural immunity you are born with.
If an infection gets past your macrophages and starts to multiply in your body, your immune system sends in the second line of attack: T- and B-cells. These are the cells that give you acquired and permanent immunity, protecting you from the same kind of infection in future.
When you get an infection, your body will rally the immune system to fight and destroy the germs. However this can take some time, especially if it is the first time you have had this specific infection. Once you have been infected the first time, your body will remember what to do and if you ever get the same infection again, it will respond more quickly. This kind of permanent immunity lasts a lifetime.
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