What is the immune system? The immune system helps to protect us
against diseases caused by tiny invaders (called pathogens) such as
viruses, bacteria, and parasites.
The immune system is made up of specialised organs, cells, and
tissues that all work together to destroy these invaders.
Some of the main organs involved in the immune system include the
spleen, lymph nodes, thymus, and bone marrow.
How does it work?
The immune system develops all kinds of cells that help to destroy
disease causing microbes. Some of these cells are specifically designed
for a certain kind of disease. All throughout the body, disease fighting
cells are stored in the immune system waiting for the signal to go to
battle. The immune system is able to communicate throughout the entire
body. When pathogens are detected, messages are sent out, warning that
the body is being attacked. The immune system then directs the correct
attacking cells to the problem area to destroy the invaders.
Antigens and Antibodies
Scientists call the invaders that can cause disease 'antigens'.
Antigens trigger an immune response in the body. One of the main immune
responses is the production of proteins that help to fight off the
antigens. These proteins are called antibodies.
How do the antibodies know which cells to attack?
In order to work properly, the immune system must know which cells
are good cells and which are bad. Antibodies are designed with specific
binding sites that only bind with certain antigens. They ignore 'good'
cells and only attack the bad ones. You can see from the picture below
that the antibodies each have a specially designed binding site. They
will only bind with the antigen that has a 'marker' that matches up
How do we get immunity?
The immune system is very smart and can adapt to new infections. Our
bodies gain immunities in two ways: natural and acquired.
Natural - When we are born, our bodies already have some immunity.
Babies get antibodies from their mother as they are growing in the womb.
They may also gain some antibodies from their mother's milk.
Acquired - Our bodies also learn immunities over time. When we get
sick, our body learns how to fight off the disease. The next time that
disease invades, our body is ready for it and can quickly produce
antibodies to prevent infection. We can also gain immunity from