The Immune
System
Activate your Prior
Knowledge!
• Discuss with a partner:
• What do you remember about the immune system?
What is it?
• How does it protect your body?
• Why does your body get sick?
• How come when you get injured, that area tends to
become red and feel warm?
If microbes are everywhere,
why aren’t we sick all the time?
• Microorganisms are EVERYWHERE!!!
• Bacteria thrives on your skin
E.g. Staphylococcus and Streptococcus species
• Bacteria colonizes your large intestines
E.g. E. coli
How many grams of bacteria inhabit our bodies?
- 1 gram, 100 gram, 1000 g?
Answer
1000 grams or 1 kilogram!!!
There are more bacteria in
and on our body than
human cells
What is the immune system?
• The body’s defense against disease causing
organisms, malfunctioning cells, and foreign
particles
• It is made up of networks of cells, tissues, and
organs
First Line of Defense
• Innate or non-specific defense responses. Including:
o
o
o
o
o
Skin
Tears
Saliva
Cilia and mucous
Gastric juice in your stomach
Skin
Skin
• The outer most layer of skin is made up of 20-30
layers of dead epithelial (skin) cells.
• Serves as a protective barrier against microbes
(bacteria and viruses) and other foreign
substances.
Tears
• Aka lacrimal secretion
• Continuously lubricates and cleanse eyes
• Contains lysozyme – an enzyme that destroys
bacteria
Saliva
• What’s the first thing you do when you cut your
finger?
• Saliva contains many chemicals that break down
bacteria
• However, thousands of different types of bacteria
can survive these chemicals
• Also contains lysozyme
Cilia and Mucus
Cilia and Mucus
• Cilia
o Propel debris-laden mucus away from nasal cavity and
lower respiratory passages
o Directs them out of the body
• Mucus
o Traps microorganisms and foreign particles from respiratory
and digestive tracts.
Stomach Acid
• Swallowed bacteria are broken down by incredibly
strong acids in the stomach
• What is this acid?
o Hydrochloric Acid (HCl)
o pH below 2
• How does the stomach protect itself from the acid?
Stomach Acid
Review
• First Line of Defense
o
o
o
o
o
Skin
Tears
Saliva
Cilia and mucous
Gastric juice in your stomach
• Acts as a barrier that prevents pathogens from
entering the body.
• As long as pathogens stay outside the body this
defensive line will handle things just fine.
Exit Slip
• What did you learn from today’s class?
• What is found in both tear and saliva
that can destroy harmful bacteria?
• How does the immune system defend
your body from infections and
diseases?
It’s time to get an STI
• Exchange body fluids with 4 other people (mix both
solutions together and then divide equally between
the two beakers)
Second Line of Defense
• AKA innate or non-specific defense (immune)
responses.
• Includes:
o
o
o
o
White Blood Cells (macrophages and neutrophils)
Inflammation
Fever
Interferon
White Blood Cells
• Macrophages
o “Big eaters”
o Phagocytic – engulfs foreign particles
• Neutrophils
o Most abundant white blood cell
o Phagocytic – engulfs foreign particles
• Once engulfed, the phagocyte breaks the foreign
particles apart in organelles called Lysosome.
• Note the difference between Lysosome and
Lysozyme, they both break down foreign particles
but Lysosome is an organelle and Lysozyme is an
enzyme.
Inflammatory Response
• Is triggered whenever body tissues are injured.
E.g. cuts, scrapes, bone fractures, infection, etc.
• Injured body cells release chemicals called
histamines, which begin inflammatory response
• Histamines are produced from basophils AND mast
cells.
Inflammation
• 4 classical symptoms:
o Redness
o Swelling
o Heat
o Pain
Main events in Inflammation
1) Vasodilation – capillaries dilate to allow blood to
flow to injured area
o This is responsible for the redness and heat.
o Allows WBCs flock to infected area like sharks to
blood
2) Dilated capillaries increase permeability, so fluid
and cells are able to leak out, this causes swelling.
Fever
• Systemic response to invading microorganisms
• Abnormally high body temperatures above 37oC
• Pyrogens are chemicals released from
macrophages, reach hypothalamus, and
temperature rises
• (Pyro = Fire)
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.
Cell before infection…
…and after.
Interferon
- Virus-infected body cells release interferon when an
invasion occurs
-
Interferon – chemical that interferes with the ability of viruses to attack
other body cells
• What happens to already
Infected cells?
Antigens
• Are substances that initiates the third line of defense
and causes your immune system to produce
antibodies
• Could be any foreign substance from the
environment
o E.g. Chemicals, bacteria, viruses, pollen
Antigen
Third Line of Defense
• Adaptive or specific defense system
• Includes:
o Humoral Immunity
• B lymphocytes  production of antibodies
o Cell-Mediated Immunity
• T lymphocytes
• Both B and T lymphocytes are produced in the
bone marrow
Bone Marrow
Third Line of Defense
• 3 important aspects:
1) It is specific
2) It is systemic
3) It has “memory”
Takes longer to activate than non-specific responses.
Humoral Immunity
• Also known as the antibody mediated
immunity
• B lymphocytes mature in the bone marrow
o Are antibody producing cells
• These are called plasma cells
o Antibodies are Y-shaped molecules
o Also manufactures “memory” cells.
Antibody
• Antibodies have receptors to bind to antigen
Cell-Mediated Immunity
• Involves living cells as protective factors
• These cells are T lymphocytes
o Recognizes infected human cells and cancer
cells
o T lymphocytes will attack these infected cells,
quickly kill them, and then continue to search for
more cells to kill
o T lymphocytes mature in the thymus gland
Thymus Gland
T Lymphocytes
• Different types of T cells
• Th – T helper cells
o Activates all aspects of immune response
• Tc – cytotoxic T cells (killer T cells)
o Highly specific, kill abnormal cells
Helper T Cells
• Primary task is to activate B cells and
cytotoxic T cells.
• BUT they themselves must be activated
Activation of Helper T Cells
Activation of Cytotoxic T
Cells
• All nucleated cells present antigens that represent
what's happening in the cell
• If something is not right (presents non-self antigen),
then the Cytotoxic T cells will detect this and kill the
cell
• Secrete specialized proteins called perforins that
poke holes in cell membrane and granzymes that
tell the cell to kill itself.
• Note* require activation factors from an activated T
helper cell to become active
Don’t copy
Activation of B cells and
production of plasma
and memory cells.
Humoral revisited
• used to fight extracellular threats
• Does so by the production of antibodies (AKA
immunoglobulins)
• Antibodies serve several functions:
- Attract phagocytes
- Complement system activation (pokes holes in
bacterial causing them to lyse)
- To neutralize certain toxins (example snake venom)
Cell mediated revisited
• used to fight intracellular pathogens or abnormal
cells
• Does so by killing infected (virus, bacteria, parasite)
cells or abnormal cells.
Scene 1
• (PLAY)
• ________ was happily riding a bicycle, when
suddenly he/she lost balance, fell and scraped
his/her knee.
• Abrasion on the skin allows for bacteria to enter into
the body.
• (PAUSE)audience answer before proceeding
• What do you think happens next?
Scene 2
• (PLAY)
• Histamines are released from basophils and mast
cells that starts the inflammation response
• How does _________’s injured area appear and feel
like now?
• (PAUSE) audience answer before proceeding
• (PLAY)
• Macrophages flock the injured area, engulfs the
bacterial cells
• Inside the macrophages, lysosomes digests the
antigen (bacteria) and presents fragments of the
antigen on its cell surface.
Scene 3
• A helper T cell comes along and binds to the
antigen complex that the macrophage cell is
presenting on its cell membrane
• The helper T cell is now happily activated and goes
on to warn the others.
• What types of cells do helper T cells goes on to
activate?
• (PAUSE) audience answer before proceeding
Scene 4
• (PLAY)
• Meanwhile, B lymphocytes finds an antigen it can
bind to specifically and waits for the helper T cell to
come and activate it.
• Once activated, the B cells will divide to produce
plasma cells and memory cells
• Plasma cells will produce an army of antibodies
• Memory cells will be on guard for future attacks by
the same antigens.
Scene 5
• Helper T cells will also go on to activate killer T cells.
• Killer T cells hunts for infected and abnormal body
cells and eliminates them.
Immunological Memory
• Primary Immune Response:
o First time the body encounters a particular
antigen
o Antibodies detected in serum between 710 days
Immunological Memory
• Secondary Immune Response:
o Upon re-exposure to the same antigen,
the body’s immune response will be much
faster, more effective and prolonged
since memory cells have been made
previously that target for these types of
antigens specifically.
o Antibodies detected in the serum
between 3-5 days.
Antibody response after exposure to antigen
What is immunity?
• Resistance to disease causing organism or
harmful substance
• Two types
- Active Immunity
- Passive Immunity
Active Immunity
- YOU produce the immune response! (e.g.
antibodies)
- Your body has been exposed to the antigen in the past
either through:
- Natural exposure (daily exposure to foreign particles)
- Artificial exposure (immunizations/vaccines)
- You fought it, you won, you remember it
- Active immunity develops slowly but lasts for years.
Passive Immunity
•
•
•
•
You DON’T produce the immune response directly
Pre-made antibody molecules enter the body
Immediate effect
Short duration (2 weeks to 1 month)
o Natural (A mother will pass
immunities on to her baby during pregnancy)
• Through what organ?
Placenta
o Artificial (antibody produced in another
host injected. E.g. anti-rabies antibodies)
Active Immunity
Passive Immunity
How long does active
immunity last?
• It depends on the antigen
• Some disease-causing
bacteria and viruses mutate
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
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
HIV
• HIV stands for Human Immunodeficiency Virus
• It is found in blood, semen, and vaginal secretions.
• The virus commonly enters the body through blood
transfusions or blood-contaminated needles and
during sexual intercourse.
HIV
• HIV attacks the helper T cells of the immune system
• Therefore, activation of B lymphocytes and
cytotoxic T cells cannot occur.
• HIV doesn’t kill you – it cripples your immune system
AIDS
• AIDS stands for Acquired Immune Deficiency
Syndrome
• It is caused by HIV
• Diseases your immune system can
normally defeat now becomes lifethreatening
• The first symptoms of AIDS are
similar to those of a cold.
Koch’s Postulates
• Proposed by Robert Koch in 1877
4 criteria to identify the specific pathogen that
caused the specific disease:
1)The pathogen must be isolated from every
patient with the disease
2) The pathogen must be isolated from the host
and grown in pure culture.
3) The pure culture of the pathogen must cause the
same disease when inoculated in healthy
susceptible animals.
4) The pathogen must be re-isolated from the
animal
EXIT SLIP
Write down one thing you’ve learned
from today’s class.
Self and Non-self
• Our immune system has an incredible ability to
recognize our cells as “self” and foreign cells as
“non-self”
• Our own cells carry distinctive “self” marker
molecules that tell the immune system to leave
those cells alone and to not destroy them.
Self and Non-self
• Recall, foreign “non-self” cells that are capable of
triggering an immune response.
Organ Transplants
• Cells and tissues from another person carries their
own self markers and therefore, will be recognized
as “non-self” in our bodies.
• This is the reason why some organ transplants are
rejected and unsuccessful.
Organ Transplants
There are 4 major types of transplants called grafts.
1. Autografts – tissue grafts transplanted from one
body site to another from the same person.
2. Isografts – graft from a genetically identical
individual. E.g. identical twin
Organ Transplants
3. Allografts – grafts from the same species but not
from a genetically identical individual
4. Xenografts – grafts from animals
Immune Disorders
Autoimmune Diseases
• Results when the body’s immune system fails to
recognize its own body cells
• It launches an attack against its own cells thinking
that they are foreign antigens
Autoimmune Diseases
• Examples of autoimmune diseases are rheumatoid
arthritis and type 1 diabetes.
• These diseases cannot be cured, they can only be
treated to relieve symptoms and prevent long-term
damage
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
Name some things people might be allergic to?
Lymphatic System
• The lymphatic system is a major part of the
immune system
• It is made up of
o Lymphatic vessels
o Lymph nodes
o Lymph
Lymphatic Vessels
• Lymphatic vessels consists of blind-ended tubes
which carries lymph in one direction – only towards
the heart.
• Lymph is made up of the fluid leaked from blood
• (lymph = clear water)
• Pathogens and cancer cells may spread
throughout the body via the lymphatic stream
Lymphoid Cells
• Lymphoid cells include lymphocytes, plasma cells
and macrophages.
Lymph Nodes
• Significant lymphoid organ
• Function:
o Filter lymph – by using macrophages to remove and
destroy microorganisms and other debris
o To help activate the immune system – lymph nodes
are sites with high density of immune cells (e.g. T and
B lymphocytes, macrophages)
Other Lymphoid Organs
Spleen
• Largest lymphoid organ
• Function:
o Site for lymphocyte proliferation
o Destroys old and defective red blood cells
Other Lymphoid Organs
Thymus
• Most active during early years of life.
• Function:
o Site of T lymphocyte maturation
Other Lymphoid Organs
Tonsils
• Simplest lymphoid organ
• Function:
o Gather and remove many of the pathogens entering
the pharynx in food or in inhaled air.