Transcript The Maintenance of Balance by the Immune System

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The Maintenance of Balance
by the
Immune System
Also Known As…
Why the aliens died at the end of
War of the Worlds and we didn’t.
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The Lines of Defence
• Your body has three lines of defence that it uses to
defend you from invading pathogens.
• A pathogen is the term used to describe any
disease-causing organism and/or entity.
• These three lines of defence are…
– The External Defence
– White Blood Cells
– Antibody Formation
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External Defenses
• The first line of defence is mainly physical with
some chemical warfare on the side.
• Skin – Impenetrable layer surrounding the body. The skin
has a low pH of 3-5.
• Mucus, Saliva & Sweat – These chemicals surround open
areas and contain lysozyme – an antimicrobial enzyme.
• Cilia – Tiny hair-like projections on cells that trap invaders
and sweep them back out of the body.
• Stomach acid/enzymes – Some pathogens, that are
ingested, make their way down the throat hit this area and
soon die because of the harshness of the environment.
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Second Line of Defence (I)
• The second line of defence is made of leukocytes
– white blood cells (WBC’s).
• Phagocytosis may be used by WBC’s to engulf
and destroy pathogens. There are WBC’s called
macrophages that do this.
• Neutrophils (kamikazes) respond to a chemical
signal released by damaged cells and engulf
invaders and release hydrolytic enzymes. The leftovers from this battle is pus.
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Macrophages in Action!
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Second Line of Defence (II)
• The action of the WBC’s initiates the
inflammatory response – a non-specific
response triggered by damaged cells that
includes swelling, redness, heat and pain. All
of these are associated with increased blood
flow and delivery of WBC’s.
• Fever – The hypothalamus turns up the
heat to about 40° which makes it hard for
invaders to survive.
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Third Line of Defence
• The third line of defence involves specific
identification and attack through complement
proteins and antibody formation.
• Complement proteins float freely in the blood
and are inactive until a pathogen is present. The
complement recognizes marker proteins on the
pathogen and do one of the following…
• Coat & immobilize pathogen.
• Puncture pathogen so it swells and bursts.
• Attach to pathogen and attract leukocyte for phagocytosis.
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Antibody Formation
• Antibodies are proteins that target, inactivate
and destroy antigens – the proteins on the
surface of pathogens.
• Antibodies are made by specialized WBC’s called
lymphocytes.
• There are two types of lymphocytes…
• T Cells - made in the bone marrow and matured in the
thymus gland (T for thymus). The role of the T cell is to
seek out intruders and signal the attack. Tattle-tales!
• B Cells - made and processed in the bone marrow.
Each B cell makes a single type of antibody. Some B cells
can become plasma cells that can produce as many as
2000 antibodies. Blasters!
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What Does the Antibody Do?
• The antibody is a Y-shaped molecule that has
two arms that attach to the antigen – the two
proteins match like key-n-lock.
• The antibody…
• Enlarges the pathogen – making it more conspicuous to
WBC’s.
• Changes pathogen shape to disallow entry into cells.
No getting through a protein portal unless you have the
perfect shape.
• HIV infects T cells so they can’t be tattled on!
They match up with and hide inside the T’s.
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Antibodies & Antigens
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How Do the T’s & B’s Work?
1. A macrophage will engulf a pathogen and push
its antigens to the outside where the T cells can
identify the antigen.
2. The T cell makes a “blueprint” of the antigen.
3. The T’s go to the B cells which read the
“blueprint” and make the matching antibody. Many
copies of this antibody are made.
4. Antibodies attach to antigen of invading
pathogens…you know what happens from here.
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T’s and B’s in Action!
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Other Interesting Immune Cells
• Killer T cells - seek and destroy microbes and cells that are infected
by viruses so the virus is destroyed and cannot reproduce.
• Suppressor T cells - signal the immune system to shut down and
conserve energy once the battle has been won.
• Memory B cells - generated during the infection which holds an
imprint of the antigen. The immune system is capable of recording the
information about an invading antigen so it does not get a foothold on
your body again.
• Most T cells and B cells die during the infection or die off within a
few days but the memory B cells remain and quickly recognize any
invader should they come back.
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The Overall Picture
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FIN