 The
Immune System and Foreign Invaders
AAAACHHOOO!! Your friend has a terrible cold, and he sneezes right
next to you without covering his mouth. Not only is this gross,
it sprays millions of cold viruses into the air around you. Luckily,
you don’t get sick. Why not? Your body has an amazing internal
defense mechanism called the immune system which protects you from
bacteria and viruses that can lead to illness. A healthy immune
system produces a variety of different cells to attack the invading
bacteria and viruses.
 
Your immune system patrols and
protects your body from harmful invaders |
If your immune system finds an invader,
it takes care of the problem |
Your blood contains many different types of cells. Red blood cells
carry oxygen to all the parts of your body. Platelets stop bleeding
by helping with blood clotting. White blood cells, known as leukocytes
(LUKE-oh-sites), make up the immune system portion of the blood.
Leukocytes are divided into three main groups:
- Granulocytes – cells which contain
granules which contain chemicals that are
used to kill bacteria and viruses
- Lymphocytes- cells which attack most
of the bacterial and viral infections in our bodies
- Monocytes - cells which become macrophages,
large cells that engulf harmful particles in our bodies
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These three types of leukocytes are even further divided into more
specialized cells, each with their own unique task in the immune
system. To learn more details about the immune system, see Additional
Resources.
How does your immune system know which cells to attack and which
cells are part of your own body? Your immune system can recognize
cells based on the proteins present on the surface of cells. Viruses,
bacteria, and other foreign cells are recognized as being different
from your own cells and are attacked by your immune system. Sometimes,
one of your own cells changes, or mutates, giving
the cell the ability to multiply continuously. Such mutations often
are the cause of cancer. Your immune system has the ability to recognize
mutated cells and attack them before they can grow into a tumor.
Not an invincible defense…
Despite the amazing ability to protect your body, the immune system
is not foolproof. Not only can certain viruses outwit your immune
system's defenses, but genetic malfunctions can result in an ineffective
immune system. The Human Immunodeficiency Virus (HIV), infects the
CD4+ T-cells, a type of lymphocyte, causing the cells to die. If
enough cells are killed, the immune system no longer functions and
the person becomes susceptible to many different diseases. An example
of a genetic disease of the immune system is lupus
which causes your immune system to mistakenly attack your body’s
healthy cells.
 
Damage to the immune system can
cause problems to go undetected |
Exposure to certain toxic chemicals can also affect your immune
system. The study of substances that harm the immune system is called
immunotoxicology (immuno: related to the
immune system, toxicology: the study of harmful substances).
After exposure to an immunotoxicant, a chemical
that harms the immune system, your body may not be able to produce
the variety or number of defense cells that it needs to protect
itself. If the immune system is damaged, it cannot attack foreign
cells such as viruses, bacteria or tumor cells that can cause health
problems.
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