does the body fight invaders?
The immune system has two approaches to attacking invaders:
Ingestion by certain migrating cells, such as macrophages and a type
of white cell known as neutrophils.
These cells are like an amoeba. They move around the
body and actually "eat" germs. Once inside the white cell,
enzymes break down and destroy the invader. Cancer cells, which the
immune system recognizes as foreign, are also combated in this way.
Binding and inactivation by protective molecules, called antibodies.
These either circulate in blood and lymph
vessels or are attached to membranes of cell surfaces, as described
previously. When they bind to foreign molecules, they make it easier
for the invaders to be broken down. In the case of viruses, the binding
can also stop the division of the virus.
Immunity to certain
diseases and infections can be developed in two ways:
1. Natural Immunity
This is the kind that you are born with. It is genetic.
There are differences in immunity among species. For example, humans
don't catch dog distemper. Dogs don't catch human colds.
are two ways to acquire immunity:
response to infection or exposure to certain substances. This means
that you actually come down with the illness, infection, or virus, but
develop the defenses to fight it off and avoid it in the future. The active
response takes several days to build up, but the protection may last
transfer of antibodies from certain vaccines or from the milk of nursing
mothers. The passive protection
from certain vaccines or mother's milk provides immediate protection,
but the effects may only last a few days or weeks.
"Sneaky Pete" Organisms:
some microbes hide from the body's defense system by inserting
themselves into the cells. The parasite that causes malaria is a good
example; it hides inside red blood cells.
Let's focus on the white blood cells for a moment, since
they are at the center of the immune system.
For more about infectious disease, check the
"Kids Health" web site;
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