The immune system is made up of specialized cells. Some are white blood cells called B cells, T cells and phagocytes, and they are produced in the bone marrow and thymus. Another component is a system of plasma proteins called the complement system. When the immune system is missing any of these parts, people are vulnerable to specific types of diseases.
Click each immune system component to learn more about it. Immune system components:
T cells are responsible for disease resistance. There are three types of T cells, each with a special purpose.
- Helper T cells detect infection and get the other cells of the immune system ready to do battle. Helper T cells also tell B cells to produce antibodies.
- Cytotoxic T cells attack virus-infected cells.
- Suppressor T cells tell the immune system when the battle with the infectious pathogens is over and to stop fighting.
B cells mature into plasma cells to make antibodies. Antibodies are highly specialized blood proteins also known as immunoglobulins. Antibodies attach themselves to invading pathogens and make them easier for other cells and complements to kill. Each antibody has a unique shape that gives it the ability to stick to a certain pathogen.
There are five main types of antibodies:
- IgM antibodies are the first to respond to an invading pathogen. They offer important protection during the early days of infection. These antibodies tend to stay in the bloodstream where they aid in killing bacteria.
- IgG antibodies are the next to respond after IgM antibodies. These antibodies are formed in large quantities and work in the blood and tissues of the body. They bind to destructive pathogens so that the immune cells (for example, macrophage) have an easier time ingesting them. IgG antibodies can pass from a mother to her unborn baby through the placenta.
- IgA is produced along the surface linings of the lungs and intestines and is secreted in body fluids such as tears, saliva, and mucus. This antibody also protects against infection in the respiratory tract and intestines. IgA passes from mothers to newborns through breast milk.
- IgE is normally present in trace amounts and is important in allergic reactions.
- IgD may be present on the surface of B cells.
Antibodies make pathogens easier to kill by alerting the immune system that the germs need to be destroyed.