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I
Immunity
Antibodies and antigens
Types of immunity
Active immunity
Vaccinations
Passive immunity
Antibodies and antigens
Invading pathogens can be
recognised by your white blood
cells as foreign because of their
surface protein molecules. These
protein molecules are called
antigens. Your white blood cells
construct Y-shaped antibodies
that lock onto the antigens,
making it easy for other white
blood cells to destroy the
pathogen.
Antibodies
When a pathogen starts to
multiply within the body,
special blood cells trigger
the production of purposebuilt antibodies to fight it.
Characteristic surface molecules (called antigens) on
the pathogen are identified, and the antibodies exactly
fit these molecules. With the antibody attached, the
pathogen is quickly destroyed by white blood cells.
Some pathogens (such as the flu virus) change their
antigens frequently, so that last year’s antibodies no
longer fit.
6H 5 Friendly fungi
6H 6 Resisting resistance
Types of immunity
Once your body has made antibodies for a particular
pathogen, the cells that made it stay available in case
they are needed again. A few antibodies remain in the
blood ‘on patrol’. If particles carrying those specific
antigens return, the antibodies lock on and a large
number of new antibodies are produced, preventing
illness. We say you are immune to that disease.
Most of the time, once you’ve recovered from an
infectious disease, you’ll be immune to it. However,
some pathogens, such as colds, influenza and
noroviruses, keep on changing their surface antigens so
they can reinfect the same people many times.
Active immunity
When the body makes its own antibodies we say it has
active immunity to that particular pathogen.
Anyone who has got sick and then recovered from the
disease will have active immunity.
Vaccines
A vaccine is an injection of dead or weakened
pathogens. These develop active immunity by
triggering the formation of antibodies but are unable
to cause the illness.
It often takes more than one dose of the vaccine to
build up full immunity to the disease.
A kitten develops the
skills needed to catch
and kill mice by training
on harmless dead mice
or toys.
The dead or weakened
pathogens in a vaccine
act like this kitten’s toy
mouse. Your body can
study the pathogen and develop antibodies to it
without any risk of illness.
Some vaccines today simply contain a shell covered
in the key surface proteins, without any viral genetic
material – very much like this toy!
Passive immunity
Young babies are very vulnerable to diseases because
they are still making their own antibodies. To help
them survive those early months, the mother's
antibodies pass through the placenta before birth and
her breast milk contains additional antibodies.
The maternal antibodies remain ‘on
patrol’ for a few months, but are
eventually destroyed by the baby’s
own immune system.
Immunity provided by maternal
antibodies is passive immunity
because the antibodies were made by
the mother, not the baby.
Sometimes patients infected with a particularly
serious disease will be given injections of antibodies
(also called immunoglobulin) to that disease. These
antibodies may have come from a person who has
recovered from the disease, or sometimes from the
blood of an animal such as a horse that has been
stimulated to produce the required antibodies.
Injections of this type provide artificial passive
immunity for a short period.
Immunity
Immunity from disease is created by antibodies, which
are specific to each pathogen. Some pathogens change
frequently, so last year’s antibodies no longer work.
Natural active immunity
Body makes own
antibodies after getting
sick and recovering from
an infection.
Natural passive immunity
Babies get short-term
protection from mother’s
antibodies via placenta
and breast milk.
Artificial active immunity
Body makes own
antibodies after injection
of dead or weakened
pathogens (vaccination).
Artificial passive
immunity
Injections of antibodies
(immunoglobulin) to fight
some serious illnesses.
6H 5 Friendly fungi
6H 6 Resisting resistance
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