Download Important Immune System Handout

The Immune System
The immune system protects the body
against disease or other potentially
damaging foreign bodies. When functioning
properly, the immune system identifies and
attacks a variety of threats, including
viruses, bacteria and parasites, while
distinguishing them from the body’s own
healthy tissue.
The Lymphatic system consists of bone
marrow, spleen, thymus and lymph nodes.
 Bone marrow produces white blood
cells, or leukocytes.
 The spleen is the largest lymphatic
organ in the body contains white
blood cells that fight infection or
disease.
 The thymus is where T-cells mature.
T-cells help destroy infected or
cancerous cells.
 Lymph nodes produce and store cells
that fight infection and disease.
Lymphocytes and leukocytes are small
white blood cells that play a large role in
defending the body against disease.
The two types of lymphocytes are:
 B-cells, which make antibodies that
attack bacteria and toxins, and
 T-cells, which help destroy infected
or cancerous cells.
Leukocytes are white blood cells that
identify and eliminate pathogens.
Your Immune System
Your immune system uses a huge army of defender cells - different types of white blood cells. You make about
1000 million of them every day in your bone marrow.
Some of these cells, called macrophages, constantly patrol your body, destroying germs as soon as they enter. This
is your 'natural' or inborn immunity. But if an infection begins to take hold, your body fights back with an even more
powerful defence of T-cells and B-cells. They give you acquired immunity, so that the same germ can never make
you as ill again.
What do T- and B-cells do?
T-cells and B-cells are highly specialised defender cells; groups of cells are
tailored to different germs. When your body is infected with a particular germ,
only the T- and B-cells that recognise those specific germs it will respond. These
selected cells then quickly multiply, creating an army of identical cells to fight the
infection. Special types of T-cells and B-cells 'remember' the invader, making you
immune to a second attack.
Your T-cells and B-cells recognise invaders by the shape of molecules, called
antigens, on the surfaces of the invaders (think logo on their team jersey). Your
immune system can produce a T-cell and B-cell to fit every possible shape (logo).
You have millions of these immune cells, one for every foreign antigen you might ever encounter.
Having recognised the invader, different types of T-cells then have different jobs to do. Some send chemical
instructions (cytokines) to the rest of the immune system. Your body can then produce the most effective weapons
against the invaders, which may be bacteria, viruses or parasites. Other types of T-cells recognise and kill virusinfected cells directly. Some help B-cells to make antibodies, which circulate and bind to antigens.
B-cells make special Y-shaped proteins called antibodies. Antibodies stick to antigens on the surface of germs,
stopping them in their tracks, creating signals that alert your body to the presence of intruders. Your body then
starts to make toxic substances to fight them. Patrolling defender cells called phagocytes engulf and destroy
antibody-covered intruders.
Your Immune Response Step By Step
1. Bacteria cells enter your body through a break in the skin.
2. The Bacteria multiply and double in numbers every 20 minutes.
3. Eventually, the mass of bacteria begin to produce enough toxin to be noticed by your immune system's
macrophages.
4. Macrophages are huge and engulf the bacteria and then digest the bacteria using enzymes. They can "eat"
about 100 bacteria each.
5. Macrophages secrete 2 different enzymes. One causes localised swelling by drawing water into the affected
area. This in known as inflammation. The 2nd enzyme they secrete is a messenger signal to other immune
cells and give information about the location of the invaders and the type of invader.
6. This 2nd signal calls in Neutrophils (suicide cells) to the battle. Neutrophils are incredibly powerful and
release toxins and other chemicals which trap and kill the invading bacteria. Unfortunately, they also
damage nearby healthy cells. Therefore, they are programmed to commit suicide (self-destruct) after about
5 days to avoid causing too much damage to your own cells.
7. If the macrophages and neutrophils are not enough to win the war against the invaders, then dendritic cells
become active and begin collecting samples of the invading bacteria. Now that the dendritic cells have
analyzed the invaders, they either call forth an army of anti-viral defenders or anti-bacterial defenders. In
this case, it calls on anti-bacterial defenders.
8. This message travels to the nearest lymph node and seeks a Helper T-Cell that has the matching shape to the
bacteria's antigen (now displayed on the outside of the dendritic cells.
9. Once a Helper T-cell match is found, the Helper T-Cell becomes activated and quickly duplicates many copies
of itself.
 Some of these T-cells will become specialized as Memory T-Cells which will remain in the lymph node
and make you immune to future invasions by this particular type of invader.
 Some become Killer T-cells and will travel to the site of the infection and begin to fight the bacteria.
 A 3rd group of Helper T-cells will travel to the center of the lymph node and activate a matching BCell to begin production of an important substance in the immune response: antibodies. The Helper
T-cells will provide some support to the B-Cells in order to help them keep pumping out antibodies
until the war is over.
10. Now millions of antibodies flood into the battle field and assist in a number of ways. 1) They disable the
bacteria making them helpless or killing them outright; 2) They stun the bacteria paralyzing them so it is
easier for the macrophages, neutrophils and Killer T-cells to attack the bacteria; 3) They also attach to the
antigens on the bacteria acting as a beacon for the macrophages and other defenders making it easier for
the defenders to target the invaders.
11. Now the defenders begin to win the war. Millions of your healthy cells may have been damaged or
destroyed by this time. The body can easily replace the damaged body cells.
12. Now that most of the immune cells are no longer needed, they self-destruct so they don't waste any of the
body's resources. The notable exception to this are the Memory Helper T-Cells and the Memory B-Cells (in
the lymph node). If the invader is ever encountered again in the body, the Memory cells can pump out antibodies immediately and overwhelm the invaders before you ever even become aware of the infection.
Draw a series of diagrams to illustrate the steps outlined in the attack against bacterial cells