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Immune System
Pre-AP Biology
Chapter 40-2
Immune System Overview
• Function: fight infection through the production
of [specialized] cells that inactivate foreign
substances or cells
• It is main defense against pathogens
▫ Recognizes, attacks, destroys, and “remembers”
each type of pathogen that enters the body
• 2 general categories:
▫ Nonspecific defenses (fortress walls of the body)
▫ Specific defenses (security guards of the body)
Nonspecific Defenses
• First line of defense: skin
▫ Most important nonspecific defense!
▫ Very few pathogens can penetrate the skin
 Must have an opening – a cut, scratch, mouth, nose
▫ Mucus, saliva, and tears have lysozyme – enzyme
that breaks down bacteria’s cell wall
▫ Oil and sweat glands produce acidic environment
▫ Mucus and cilia in nose and throat trap and push
pathogens away from lungs
▫ Acid and enzymes destroy bacteria that make it to
your stomach
Nonspecific Defenses
• Second line of defense: inflammatory response
▫ Reaction to tissue damage caused by injury/infection
▫ When pathogens are detected:
 White blood cells flood area through blood vessels near
wound
 Many WBC are phagocytes – engulf and destroy
 Releases chemicals that increase core body temperature
(fever)
 Many pathogens only survive in narrow temp. range
 Increased temp also increases heart rate = more WBC
Nonspecific Defense to Viruses
• Sometimes, virus-infected cells produce a group
of proteins that help other cells resist infection:
Interferons
▫ Named this because they “interfere” with growth
of the virus
▫ Slows the progress of infection and gives specific
defense system time to respond
Specific Defenses
• Called “immune response”
• Triggered by antigens
• 2 types of lymphocytes
▫ B lymphocytes (B cells) – work in body fluids
 Humoral immunity
▫ T lymphocytes (T cells) – work in living cells
 Cell-mediated immunity
Humoral Immunity
• B cells detect pathogen and multiply rapidly
▫ Produces large numbers of plasma cells and
memory B cells
• Plasma cells release antibodies (proteins that
recognize and bind to antigens – recall blood
types!)
▫ Antibodies carried in the blood stream to attack
• Memory B cells remain capable of producing
antibodies specific to that pathogen after
exposure
Antibody Structure
• Antibody is shaped like a “Y” and
has two identical antigen binding
sites
▫ Differences in amino acids affect
shape of binding sites
▫ Shape of binding site is how
antibody recognizes antigen
▫ Healthy adult can produce about
100 million different types of
antibodies!
Cell-Mediated Immunity
• Primary defense against own cells when cancerous
or infected
• Also important for fighting fungi and protists
• Process: T cells divide and differentiate into…
▫ Killer T cells – destroy bacteria, fungi, protozoan or
foreign tissue with the antigen
▫ Helper T cells – produce memory T cells
▫ Suppressor T cells – shut down killer T cells after
pathogenic cells brought under control
▫ Memory T cells – cause response if same antigen
enters again
Transplants
• Killer T cells make organ transplants difficult
▫ Recognize new organ as foreign and attack it
 Called “rejection”
▫ To prevent rejection, donor should have cell
markers nearly identical to recipient; and
▫ Recipient usually takes drugs for the rest of their
life to suppress cell-mediated immune response.
Acquired Immunity
• Remember Jenner’s smallpox??
▫ Cowpox infection to create immunity to smallpox
• Can be active or passive
Active vs. Passive Immunity
Active
Passive
• Type of immunity produced
by reaction to a vaccine
• Vaccination: injection of
weakened or mild form of
pathogen
• Stimulate immune system to
create plasma cells
• Plasma cells are ready to make
specific antibodies
• Appears AFTER exposure
• Can be natural or deliberate
• Antibodies produced by other
animals injected into the
bloodstream
• Lasts for short time – body
eventually destroys them
• Can be natural or deliberate
• Natural: from mother to fetus
or in breastmilk
• Deliberate: vaccine
▫ Tropical diseases
▫ Rabies