The Immune System: First Line of Defense

Immune System Definition

• The immune system is the body's defense against disease-causing organisms, malfunctioning cells, and foreign particles.

First Line of Defense

• The first line of defense includes barriers that prevent pathogens from entering the body.

Skin

• The epidermis, is the dead, outer layer of skin and forms a shield against invaders
• It secretes chemicals that kill potential invaders
• You shed approximately 40,000 to 50,000 skin cells every day

Mucus and Cilia

• Mucus traps foreign particles and bacteria in the respiratory system
• Cilia are hair-like structures that sweep mucus into the throat to be coughed out or swallowed

Saliva

• Saliva contains chemicals that break down bacteria
• Thousands of different types of bacteria can survive these chemicals

Stomach Acid

• Swallowed bacteria are broken down by incredibly strong acids in the stomach
• The stomach produces a coating of special mucus to protect itself from the acid
• Escherichia coli is common and plentiful in all digestive tracts, helps digest material and is technically outside the body
• E. coli can cause harm if introduced in an unnatural manner

Second Line of Defense

• The second line of defense involves internal defenses to combat pathogens that have entered the body.

White Blood Cells (WBCs)

• White blood cells attack invaders that get inside the body
• WBCs circulate in the blood and enter tissues if invaders are detected

WBC: Phagocytes

• Phagocytes are responsible for engulfing foreign particles
• Organelles called lysosomes break down the foreign particles within the phagocyte

Virus

• Viruses hijack organelles within body cells to replicate themselves
• Infected cells eventually burst, releasing thousands of viruses, that then infect new cells.

Virus: Interferon

• Virus-infected body cells release interferon when under attack
• Interferon is a chemical that interferes with the ability of viruses to attack other body cells

WBC: T-Cells

• T-cells, also known as "natural killer" cells, recognize and attack infected human cells and cancer cells
• They kill infected cells quickly and continue searching for more cells to kill

Inflammatory Response

• Injured body cells release chemicals called histamines, initiating the inflammatory response
• Capillaries dilate
• Pyrogens are released, travel to the hypothalamus, and cause temperature to rise
• Pain receptors activate
• WBCs flock to the infected area

Two Divisions of the Immune System

• Cell-mediated immune system efforts are from WBCs known as phagocytes and T-cells
• Protective factor = living cells
• Phagocytes eat invaders
• T-cells kill invaders
• Antibody-mediated immunity is the other half of the immune system.
• It is controlled by antibodies
• It is the third line of defense in the immune system

Third Line of Defense

Antibodies

• Most infections won't make it past first & second levels of defense
• Antibodies aid those that do and trigger antibodies
• Proteins latch onto damage, clump, and slow foreign particles
• Each antibody binds only to one specific binding site, known as an antigen

Antibodies & WBCs

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

Immunity

• New particles take longer to identify, causing illness until a new antibody is crafted
• Old particles are quickly recognized, preventing illness from that invader, creating immunity
• Immunity is the resistance to a disease-causing organism or harmful substance
• Immunity can be Adaptive or Innate
• Adaptive immunity can be divided into:
• Natural
• Passive (maternal)
• Active (infection)
• Artificial
• Passive (antibody transfer)
• Active (immunization)

Active Immunity

• Living organisms produces the antibodies
• Body has been exposed to the antigen, either by:
• Exposure to the actual disease causing antigen where you fought it and you won
• Planned exposure to a form of the antigen that has been killed or weakened and you detected it, eliminated it, and remember it

Active Immunity: Vaccine

• Antigens are deliberately introduced into the immune system to produce immunity
• Because the bacteria has been killed or weakened, minimal symptoms occur
• Vaccines have eradicated or severely limited several diseases like polio and smallpox
• How long active immunity can last depends on the antigen
• Some disease-causing bacteria multiply into new forms that the body doesn't recognize, requiring annual vaccinations (like the flu shot)
• Booster shots remind the immune system of the antigen
• Others last a lifetime, such as chicken pox
• In 1918, a deadly strain of flu, called the Spanish Influenza, spread across the globe
• It infected 20% of the human population and killed 5%, about 100 million people
• The CDC recommends certain vaccines, but many individuals go without them
• The vaccine for meningitis is recommended for all college students and infects 3,000 people in the U.S., killing 300 annually

Passive Immunity

• Antibodies are not produced by you
• A mother will pass immunities onto her baby during pregnancy
• The antibodies protect the baby for a short period after birth while its immune system develops
• Lasts until antibodies die

Passive Immunity: Allergies

• The immune system mistakenly recognizes harmless foreign particles as serious threats
• This launches an immune response, leading to sneezing, runny nose, and watery eyes
• Antihistamines block the effect of histamines, bringing relief

Acquired Immune Deficiency Syndrome (AIDS)

• Caused by the Human Immunodeficiency Virus (HIV)
• Discovered in 1983
• Specifically targets and kills T-cells
• Because normal body cells are unaffected, the immune response is not launched
• HIV virus doesn't directly kill; it cripples the immune system
• With a shut down immune system, common diseases become life-threatening
• Can show no effects for months up to 10 years
• Transmitted by sexual contact, blood transfusions, and contaminated needles
• As of 2007, it affected an estimated 33.2 million people