What is Passive Immunity?
This occurs when antibodies are passed into your body from a source, other than yourself. For example, as a baby, you can receive antibodies from your mother's milk, or even from the placenta, whilst still in utero. This is called natural passive immunity. This type of immunity however, is only temporary, as the antibodies are removed by the liver.
You can also achieve passive immunity artificially from an injection that you would receive for protection from various conditions, such as tetanus. Again, this protection against disease is only temporary.
What is Active Immunity?
This is when the body creates its own antibodies after exposure to an antigen. Once exposed to infection, the body begins an immune response. This process though, is slow, so you can begin to suffer symptoms of your illness, unless of course, you have been exposed to the same antigen before, in which case your body's response is fast and no - or only a few symptoms - may appear.
How does Vaccination work?
Vaccination introduces the antigen in some form into the body so that antibodies are produced without you experiencing any symptoms of the disease. It can work in different ways:
- Living pathogens that will multiply, but have been weakened, eg. Rubell
- Artificial antigens that have been grown in a laboratory fermenter and harvested as a vaccine
- Toxoids such as tetanus in which the toxin is made harmless by using formaldehyde
- Dead micro-organisms that though harmless, still produce an antibody response
All of these options produce an active immune response because it causes you to synthesise your own antibodies.
How does Infection get into your body?
Your body has many defence shields to prevent infection:
- Tears protect the eyes
- Your skin
- Cell layers that cover the mouth, vagina, nose and alimentary canal
- Acid in your stomach
- Clotting mechanism in the blood
If the infection gets past any of these and antigens infect and reproduce within your bloodstream then there are two further processes that can destroy the pathogen - your immune response and phagocytosis.
What is phagocytosis?
Simply put, phagocytosis is when a plasma membrane forms a depression around the antigen in the bloodstream, which then surrounds it, pinching it off to form a vacuole, preventing the antigen from reproducing. Phagocytosis only occurs in a few specialised cells in the body and these specialised cells cause the vacuole to degrade and die.
ImmunodeficiencyThis occurs when the immune response is severely weakened or completely absent. Transplant patients take special drugs to suppress their immune system to prevent rejection of their transplanted organ, or there are those that have to take chemotherapy drugs to treat cancer and these people can be severely immunocompromised. There are also some people with acquired immunodeficiency syndrome (AIDS) that is caused by HIV, a virus that indirectly attacks the immune system.
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