What are the major functions of
the Immune System?
 Regulation and Protection
 Fight disease
 Prevent future infections
What is a pathogen?
 Any disease causing agent
 Ex: bacteria, viruses, parasites, toxins, fungi
What is the difference between
innate and adaptive immunity?
 Innate immunity – target
any pathogen
(nonspecific); found in
all organisms
 Adaptive immunity –
targets one specific
pathogen (specific) –
varies from individual to
individual (genetics!)
FIRST LINE OF DEFENSE:
NONSPECIFIC EXTERNAL DEFENSES
 Skin – water-proof barrier
 Sweat
 Tears
 Cilia – respiratory tract
 Mucous membranes
 Acids in stomach
 Commensal microbes living
on the skin
Ex: INTERNAL DEFENSES
 Macrophages – large phagocytic white blood cells
 Natural Killer (NK) cells – WBCs that target cancer
cells
 Interferons – proteins produced by viral infected cells
to limit spreading of viral infection
How Interferons Work:
What is the role of a phagocyte
(macrophage)?
 Nonspecific White blood cells
 Engulf and destroy any material they do not
recognize
 Act as “Antigen Presenting Cells” following
phagocytosis for possible specific response
SECOND LINE OF DEFENSE:
NONSPECIFIC Inflammatory Response
SECOND LINE OF DEFENSE:
Inflammatory Response
 FUNCTION: to disinfect and clean injured tissues;
prevent spreading of infection
 Triggered by any damage to tissue
 Can be localized or widespread
 Results in Redness, Heat Production, Swelling
Why is the inflammatory response
considered to be innate immunity?
 The response is the same regardless of whether the
invader has been previously encountered
THIRD LINE OF DEFENSE:
ADAPTIVE IMMUNITY
 “custom-tailored” defenses to each specific invader
 Provides a strong and long lasting defense
 Lymphocyte activity (B-cells and T-cells)
What is an antigen?
 Any molecule that elicits an adaptive (specific)
immune response
 Ex: parts of microbes, proteins on microbes, toxins,
mold, pollen
 Foreign Molecules!
What are the two major divisions
of mammalian adaptive immunity?
 Cell-Mediated – T cells (lymphocytes)
 Humoral – B cells (lymphocytes)
How is the specific immune
response triggered?
 Non-specific phagocytes present antigens from
pathogens to lymphocytes (B and T cells)
 Interconnectedness between nonspecific and
specific defenses!
Cell-Mediated Response
 Specific T-cells are
developed to target
specific antigens
 These T-cells trigger
the destruction of
those pathogens
and infected cells
through cell-cell
interactions
How do cytotoxic T cells destroy
infected cells?
 Following recognition and binding to the
MHC/antigen complex on infected cells, T-cells will
“shoot” a perforin complex into the membrane of cells
which triggers cell death via lysis or apoptosis
Cytotoxic T cell Activity
What about T-helper cells?
 Lymphocytes (T-cells) that support the action of the
specific immune response (humoral and cell
mediated)
 Cell-cell communication (autocrine AND juxtacrine)
Adaptive Immune Response OVERVIEW
Humoral Response
 Specific B-cells are
developed that produce
and secrete antibodies
that bind to specific
antigens.
 These antibodies bind to
the antigens on
pathogens and target
them for destruction by
T-cells, phagocytes, or
prevent them from
causing further infection
How is the “perfect” antibody
found and produced?
How are the perfect T-cells found?
How is the correct B and T cell
discovered for a specific antigen?
 CLONAL SELECTION
 T-cells and B-cells have specific receptors on their cell
membranes that respond to specific antigens
 Only cells whose receptors react with the specific
antigen undergo rapid cell division
 This results in a MASSIVE and EFFICIENT adaptive
immune response
What is an antibody?
 “Y-shaped” protein produced by B-cells
 Attaches to one specific antigen and helps counter its
effects
**One gene can synthesize millions of
Different antibodies via alternative splicing**
Antibodies do not kill pathogens,
what do they do?
 Antibodies
bind to
antigens and
prevent further
infection
 Mark
pathogens for
destruction by
macrophages
How does the production of
memory cells help promote long
lasting immunity?
 B-lymphocytes (and some T-lymphocytes) produce
memory cells which last for a very long time
 Activated by a second exposure to the antigen
 Stronger and faster response
What is the purpose of a vaccine?
How are vaccines produced?
 To prevent infection from a specific pathogen by
introducing the antigens of the pathogen to the
immune system
 Two types of vaccines:
 Live-attenuated viruses (weakened)
 Dead viruses
What happens in your body when
you receive a vaccination?
 Humoral immune response is triggered
 Production of antibodies and memory cells
 **Why is it that vaccines do NOT always provide life-
long lasting immunity?**
 Mutations in the pathogens DNA changes their
antigens, making the produced antibodies ineffective
What is the difference between
active and passive immunity?
 Passive Immunity:
receiving premade
antibodies; short lasting
 Ex: breastmilk, antibody
injection; antivenom
 Active Immunity: the
person’s own immune
system actively produces
antibodies; long lasting
 Ex: vaccine, natural
exposure to a pathogen
What about Allergies?
 Immune response to non-pathogenic foreign
molecules (allergens)
 Inflammatory response activated (often in the
respiratory system) due to release of histamine
 Treatment: antihistamines, epinephrine
What is an autoimmune disease?
 Immune response to populations of body cells
 Treatments: immunosuppressant drugs; alleviation of
specific symptoms
 Ex: Type 1 diabetes mellitus: cytotoxic T cells attack
insulin producing cells
 Ex: MS: T cells react against myelin sheath
 Ex: Rheumatoid arthirtis: antibodies target cartilage
and bone cells at joints
Prokaryotes Immune Systems
 Restriction Enzymes!
 Cut up foreign DNA (of a bacteriophage) at specific
restriction site sequences
 Protect their own DNA by adding methyl groups to the
same restriction sites (preventing cutting)
 Bacteriophages have evolved mechanisms to evade this
defense
Prokaryotic Immunity
 A: Restriction Enzyme is
successful
 B: Evolved mechanisms
in bacteriophages to
evade degradation
Fungi and Plants Immunity
 Rely on the production of a wide variety of chemicals
that can cause unpleasant effects in would-be
pathogens and predators
Fungi – Death Cap Mushroom
 If consumed, can cause
irreversible liver failure
in humans
Fungi – Penicilium genus
 Produce antibiotics (like penicillin) to protect against
bacterial infections
Plants – Defenses against
Pathogens
 First line of defense – physical barrier of epidermal
cells
 If that fails, plant cells are damaged by infection…
 In response, plants…
 Seal off the infected areas
 Release microbe-killing chemicals to signal local cells to
do the same -> infected and local cells induce cell death
 Plant hormones also secreted to prevent systemic
spreading of the pathogen to other parts of the plant
AND to stimulate production of defense chemicals
Figure 33.13B_s6
5
3
Enhanced
local
response
1
Binding of the
pathogen’s Avr
protein to the
plant’s R protein R protein
6
4
Avirulent
pathogen
Avr protein
2
Signal
transduction
pathway
Hormones
Additional
defensive
chemicals
Signal
transduction
pathway
Recognition between R and Avr proteins, Systemic acquired
leading to a strong local response
resistance
Plant defenses against herbivores
 Herbivores are animals that mainly eat plants.
 Plants use chemicals to defend themselves against
herbivores and pathogens.
 Plants counter herbivores with
 physical defenses, such as thorns, and
 chemical defenses, such as distasteful or toxic
compounds.
Figure 33.13A_s5
Plant defense against herbivores
5
4
Wasp is attracted
The
wasp
lays
eggs
3
Synthesis
and release
of chemical
attractants
Plant cell
1
Damage to plant
and chemical in
caterpillar saliva
2
Signal
transduction
pathway
Animals – Invertebrates - Insects
 Innate Immunity Only (LACK adaptive immunity)
 Examples of Physical Barriers:
 Exoskeleton
 Low pH
 Lysozyme enzyme secretion to break down bacterial cell
walls
 Immune cells capable of phagocytosis
 Production of antimicrobial proteins to help destroy
invaders