The Human Immune System

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What is the immune system?

• The body’s defense against disease causing organisms, malfunctioning cells, and foreign particles

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The First Line of Defense�~Skin~

• The dead, outer layer of skin, known as the epidermis, forms a shield against invaders and secretes chemicals that kill potential invaders
• You shed between 40 – 50 thousand skin cells every day!

• As you breathe in, foreign particles and bacteria bump into mucus throughout your respiratory system and become stuck
• Hair-like structures called cilia sweep this mucus into the throat for coughing or swallowing

The First Line of Defense�~Mucus and Cilia~

Don’t swallowed bacteria have a good chance of infecting you?

What’s the first thing you do when you cut your finger?

The First Line of Defense�~Saliva~

• Swallowed bacteria are broken down by incredibly strong acids in the stomach that break down your food
• The stomach must produce a coating of special mucus or this acid would eat through the stomach!

The First Line of Defense�~Stomach Acid~

Think of the human body as a hollow plastic tube…

The food is digested within the hole in the tube, but it never actually enters into the solid plastic material.

Tube inner surface ~Digestive System~

Plastic interior ~Body~

Tube outer surface ~Skin~

Escherichia coli�is common and plentiful in all of our digestive tracts. Why are we all not sick?

The Second Line of Defense�~White Blood Cells~

• If invaders actually get within the body, then your white blood cells (WBCs) begin their attack
• WBCs normally circulate throughout the blood, but will enter the body’s tissues if invaders are detected

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• These white blood cells are responsible for eating foreign particles by engulfing them
• Once engulfed, the phagocyte breaks the foreign particles apart in organelles called ________

White Blood Cells

~Phagocytes~�

Lysosomes

Where could invaders hide from phagocytes?

Viruses

Viruses enter body cells, hijack their organelles, and turn the cell into a virus making-factory. The cell will eventually burst, releasing thousands of viruses to infect new cells.

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The Second Line of Defense�~Interferon~

• Virus-infected body cells release interferon when an invasion occurs
• Interferon – chemical that interferes with the ability to viruses to attack other body cells

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What happens to already infected cells?

White Blood Cells�~T-Cells~

• T-Cells, often called “natural killer” cells, recognize infected human cells and cancer cells
• T-cells will attack these infected cells, quickly kill them, and then continue to search for more cells to kill

The Second Line of Defense�~The Inflammatory Response~

• Injured body cells release chemicals called histamines, which begin inflammatory response
• Capillaries dilate
• Pyrogens released, reach hypothalamus, and temperature rises
• Pain receptors activate
• WBCs flock to infected area like sharks to blood

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Two Divisions of the Immune System

• The efforts of the WBCs known as phagocytes and T-cells is called the cell-mediated immune system.
• Protective factor = living cells
• Phagocytes – eat invaders
• T-cells – kill invaders

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Two Divisions of the Immune System

• The other half of the immune system is called antibody-mediated immunity, meaning that is controlled by antibodies
• This represents the third line of defense in the immune system

The Third Line of Defense�~Antibodies~

• Most infections never make it past the first and second levels of defense
• Those that do trigger the production and release of antibodies
• Proteins that latch onto, damage, clump, and slow foreign particles
• Each antibody binds only to one specific binding site, known as an antigen

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Antibody Production

• WBCs gobble up invading particles and break them up
• They show the particle pieces to T-cells, who identify the pieces and find specific B-cells to help
• B-cells produce antibodies that are equipped to find that specific piece on a new particle and attach

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Immunity

• New particles take longer to identify, and a person remains ill until a new antibody can be crafted
• Old particles are quickly recognized, and a person may never become ill from that invader again. This person is now immune.

What is immunity?

• Resistance to a disease causing organism or harmful substance
• Two types
• Active Immunity
• Passive Immunity

Active Immunity

• You produce the antibodies
• Your body has been exposed to the antigen in the past either through:
• Exposure to the actual disease causing antigen – You fought it, you won, you remember it
• Planned exposure to a form of the antigen that has been killed or weakened – You detected it, eliminated it, and remember it

What is this second type of exposure called?

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Vaccine

• Antigens are deliberately introduced into the immune system to produce immunity
• Because the bacteria has been killed or weakened, minimal symptoms occur
• Have eradicated or severely limited several diseases from the face of the Earth, such as polio and smallpox

How long does active immunity last?

• It depends on the antigen
• Some disease-causing bacteria multiply into new forms that our body doesn’t recognize, requiring annual vaccinations, like the flu shot
• Booster shot - reminds the immune system of the antigen
• Others last for a lifetime, such as chicken pox

Think the flu is no big deal?

• Think again…
• In 1918, a particularly deadly strain of flu, called the Spanish Influenza, spread across the globe
• It infected 20% of the human population and killed 5%, which came out to be about 100 million people

Do we get all the possible vaccines we can?

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• Although the Center for Disease Control (CDC) recommends certain vaccines, many individuals go without them
• Those especially susceptible include travelers and students
• Consider the vaccine for meningitis, which is recommended for all college students and infects 3,000 people in the U.S., killing 300 annually

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Passive Immunity

• You don’t produce the antibodies
• A mother will pass immunities on to her baby during pregnancy - through what organ?
• These antibodies will protect the baby for a short period of time following birth while its immune system develops. What endocrine gland is responsible for this?
• Lasts until antibodies die

Why doesn’t the mother just pass on the WBCs that “remember” the antigens?

Immune Disorders�~Allergies~

• Immune system mistakenly recognizes harmless foreign particles as serious threats
• Launches immune response, which causes sneezing, runny nose, and watery eyes
• Anti-histamines block effect of histamines and bring relief to allergy sufferers

Aquired Immune Deficiency Syndrome

• Caused by the Human Immunodeficiency Virus
• Discovered in 1983
• Specifically targets and kills T-cells
• Because normal body cells are unaffected, immune response is not launched

AIDS�~The Modern Plague~

• The HIV virus doesn’t kill you – it cripples your immune system
• With your immune system shut down, common diseases that your immune system normally could defeat become life-threatening
• Can show no effects for several months all the way up to 10 years

AIDS�~The Silent Spread~

• Transmitted by sexual contact, blood transfusions, contaminated needles
• As of 2007, it affects an estimated 33.2 million people

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