The immune system protects your body against infection and disease. It recognises what cells belong to our body and what cells are foreign.
What is the immune system?
The immune system protects your body against infection and disease. It recognises what cells belong to our body and what cells are foreign. The immune system acts to get rid of the invading cells so that they do not bring you harm. This includes viruses, bacteria, parasites and toxins (poisons). Your immune system also helps to destroy cells that are old, damaged or have become abnormal.
The immune system is made up of special organs, cells and chemicals that fight infection. The main parts of the immune system that actively fight infection include:
- White blood cells
- The lymphatic system
- The spleen
- The thymus
- The bone marrow
What are lymphocytes?
Lymphocytes are a type of white blood cell and are a major component of the lymphatic system. Lymphocytes are divided into two types: B-lymphocytes or T-lymphocytes (also called B-cells or T-cells), and function to ﬁght infection and prevent disease. They are an important part of a healthy immune system.
- B lymphocytes (B-cells): normal functioning B-cells transform into highly specialised cells called plasma cells in the face of infection. Plasma cells manufacture antibodies which function to ﬁght infections.
- T lymphocytes (T-cells): directly attack foreign invaders such as bacteria and viruses, and also kill cancer cells and rid them from the body.
Lymphocytes can be found in the blood however, the majority of them are normally circulating within the lymphatic system. They are mainly stored in our lymph nodes.
Parts of the immune system
Lymph: is the clear fluid that flows around the lymphatic system. It is formed from plasma. Lymph has an important function where it captures the bacteria and brings them to lymph nodes. The bacteria are then destroyed.
Lymph nodes: are small bean shaped structures. They are usually around 1cm long. There are thousands of them located throughout the body. Lymph nodes filter lymph from nearby parts of the body.
Spleen: the spleen is a pear-sized organ that lies just under your rib cage on the left-hand side of your body. Cells that live in the spleen remove germs and old, damaged cells from your blood.
Thymus: the thymus gland is a small butterfly-shaped gland in your chest. It sits behind your breastbone. T-cells develop and mature into fully working T-cells within the thymus gland.
Bone marrow: is the spongy material at the centre of many of your bones. Its function is to make the blood cells you need. These include red blood cells, platelets, and the various types of white blood cells.
Tonsils and adenoids: tonsils are two lymph nodes located on each side of the back of your throat. They function as a defence mechanism and help prevent your body from getting an infection. Adenoids are glands located behind the nasal cavity. They look like small lumps of tissue and help protect the body from viruses and bacteria.
Immunity – our body’s protection
The immune system is made up of different parts and these work in different ways. There are also different types of immunity that protect our body. These are called innate immunity and acquired immunity.
Innate immunity is the immunity you are born with. This includes physical barriers and phagocytes.
- Physical barriers prevent organisms getting into the body. Physical barriers include skin and mucous membranes. Mucous membranes are the soft, moist linings of areas such as your mouth, nose, gut and breathing passages. Fluids such as saliva and tears help with washing away of the germs. Our stomach acid helps to destroy any germs that you swallow.
- Phagocytes can ingest and destroy germs and any cells that are no longer of any use to your body. Types of phagocytes are called macrophages and neutrophils.
- Macrophages develop from white blood cells called monocytes. They ingest any germs and any old, dead or damaged cells.
- Neutrophils are found in the bone marrow and bloodstream but move into tissues when there is an infection.
Acquired immunity is the immunity you develop throughout your life as you get exposed to infections. This type of immunity prevents you from getting the same infections again.
Vaccinations expose you to a small dose or inactivated form of the infection so your immune system can recognise this infection in the future.
Lymphocytes are a very important part of the acquired immune system.
Lymphocytes are important in giving you immunity to an infection when you have already had that infection in the past.
Antibodies are proteins made by lymphocytes to fight infection. B Lymphocytes (B-cells) are made in the bone marrow. They live mainly in lymph nodes and the lymphatic system. B lymphocytes turn into plasma cells.
Plasma cells produce antibodies that are known as immunoglobulins. Antibodies fight infection by sticking to the proteins of the invading germs. These proteins are called antigens. Antibodies fight infection by stopping germs getting into our cells, telling other immune cells that the cell should be killed and switching on proteins to destroy the cells. Once the infection is gone, many of the B cells and plasma cells die. A few cells remain called memory cells. They will help fight infection in the future.
- T Lymphocytes (T-cells) are made in the bone marrow but mature in the thymus gland. They then live in the lymph nodes. Each T-cell can only recognise one antigen. If it comes into contact with that antigen it makes copies of itself. The copies work in different ways.
- Cytotoxic T-cells kill the germ and they also look out for abnormal cells of your body that they will then kill.
- Helper T-cells signal to B-cells to make more antibodies and by switching on macrophages and neutrophils.
- Memory T-cells remain when the infection is gone. They remain so they can respond to that infection in the future.
- NK cells (natural killer) kill cells that have been infected by a virus or are turning into cancer.