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The Immune System
What is the Immune System?
What is the Immune System?
The immune system is made of special cells, proteins, tissue
and organs, which defend people against foreign material and
microorganisms
The Immune System protects the body
from injury….
• Injury can be due to….
A pathogen is anything that
causes disease
Four major types of pathogens
•
•
•
•
Bacteria
Viruses
Fungi
Internal parasites
virus
Parasitic worms,,,
bacteria
Fungus
Allergen
• a non-parasitic substance that the body perceives as a threat, triggering a
specific immune response
• stimulates the production of IgE antibodies
• Possible reactions: sneezing, coughing runny nose, sore throat, diarrhea,
vomiting, itching, and hives
• Severe reactions: breathing difficulty, death
ragweed
Examples of allergens
Dust mites
pollen
cat dander
Ragweed
Food Allergies
• The Food and Drug Administration recognizes 8 foods as being common
for allergic reactions: peanuts, tree nuts, eggs, milk, shellfish, fish, wheat
and their derivatives, soy and their derivatives, and sulphites (often found
in flavors and colors in foods) at 10ppm parts per million) and over
Milk allergy is caused by
an enzyme deficiency
(lactase deficiency)
Unlike other body systems,…..
• The immune system is not an organ system
like the digestive system, with a one-way
discrete “tract.”
• Its structures are a collection of molecules and
trillions of immune cells…. all circulating
throughout the body
Organs/structures of the Immune
System
Composition of Blood
Blood Smear
Monocyte
Red blood cell
Neutrophil
Lymphocyte
Pluripotent cells
from bone
marrow give rise
to many types of
cells
Where are blood cells made?
The Big Picture
Body Defenses
• 1. Nonspecific Defense System- responds
immediately to protect the body from foreign
substances (innate immunity)
• 2. Specific Defense System (adaptive
immunity)-defends against SPECIFIC foreign
substances--- and must be primed by an initial
exposure to a foreign substance
Examples of Defense
• Non-specific Defense:
– Surface membrane barriers
– Phagocytes
– Natural Killer cells (NK)
– Inflammatory Response
• Specific Defense:
– Lymphocytes
– Antibodies
– monocytes
“Innate immunity” vs. “adaptive
immunity”
• Innate immunity:
• The body recognizes and responds to a foreign
substance, but the response is the SAME each time
• Adaptive immunity:
– the body recognizes and destroys foreign
substances, but the response improves each time
the foreign substance is encountered
INNATE VS. ADAPTIVE IMMUNITY
• Innate: rapid response (hours),constant
• Adaptive: slow response (days to weeks),
improves over time
What do these pictures have to do
with the immune system?
sebum
Skin
Tears
Stomach acids
Innate Defense System
•
•
•
•
•
Skin
Mucous membranes
The inflammatory response (heat, redness, swelling)
phagocytosis
NK cells
• The skin,mucous membranes, and the inflammatory
response are always prepared to defend the body
The first line of defense is the skin
and mucous membranes
• The keratinized epidermis is a strong barrier to
microorganisms that swarm on the skin
• Acid pH of skin inhibits bacterial growth
• Sebum contains chemicals which are toxic to bacteria
Blood, sweat, tears, and stomach
acid
• The stomach mucosa secretes HCl and
proteases. Both kill pathogens
• Saliva and tears contain lysozyme, an enzyme
that kills bacteria by destroying the cell wall
• Sticky mucus traps many pathogens that enter
digestive and respiratory tracts
Effects of pH and temp on bacteria
The Inflammatory Response
• A non-specific response to tissue injury
• Types of injury: physical trauma, heat, chemicals,
and infection due to bacteria and viruses
• Signs: redness, heat, swelling, pain
• In asthma, there’s inflammation of another kind;
symptoms include bronchoconstriction, mucus
production
Acute vs. chronic inflammation
• Acute: extreme reaction, happening all of a
sudden
• Acute asthma: an attack, which could lead to
death
• Chronic: happening over a long period of time
• Chronic asthma: asthma symptoms occur over
a long period of time
What is inflammation?
• An inflammation is the immune system's response to
invading organisms or substances. These may be bacteria,
viruses, fungi, allergens, or, in the case of an autoimmune
disease, the bodies’ own tissue. A typical example of
inflammation is the painful red swelling associated with acne.
Signs of inflammation
• heat
redness
swelling
pain
What is “trauma?”
The Inflammatory Response
• Trauma- mast cells produce histamine
capillaries dilate and become leaky--- fluid
enters the tissues- (swelling)pain receptors
are stimulated (pain)-- phagocytes are
attracted to area by chemical signals(chemotaxis) dilation of blood vessels
increases blood flow to area (thus, redness,
heat, and pain) ---> bacteria are destroyed---------- tissue repair
Infection of the Lungs
• Neutrophils fill the alveoli in this case of a
patient with acute bronchopneumonia
Other inflammatory effects
• An increase in local temperature has an
antibiotic effect.
• A large number of signaling molecules
(chemokines) are released by affected cells to
“call” more cells (WBC) to the area.
Evidence of inflammation
• The pus that often results is the debris of dead
bacteria, leukocytes and other cells.
The inflammatory response
• http://www.sumanasinc.com/webcontent/anim
ations/content/inflammatory.html
http
Ht ://www.youtube.com/watch?v=CmbWE3jLUgM
www.youtube.com/watch?v=d-3114YDZIU&NR=1
Two types of defense
• Cellular defense: cells engulf foreigners
• Humoral (antibody) defense- foreign antigens
stimulate the production of antibodies
Phagocytosis
Cellular Defense
• Phagocyte----a WBC which engulfs foreign particle
• Phagocytosis: microbe binds to phagocyte phagocyte pulls
microbe inside-a vesicle containing microbe antigen forms
(phagosome)-vesicle is fused with lysosome
(phagolysosome)-- microbe in vesicle is digested by
enzymes-undigested material removed by exocytosis
Eating or attacking?
• An amoeba is eating algae
Natural Killer Cells (NK)
• recognize certain sugars on target cell membrane’s surface.
• attack the target cell’s membrane and release a lytic
chemical called perforins--- causing disintegration of target
cell membrane and nucleus
An "NK" cell (N) attached to a "target" cell "T".. The NK cell will kill the now helpless
target cell quickly, by the injection of deadly perforin. (Courtesy of Dr. G. Arancia and K.
Malorni, Rome)
Why do babies get sick more often
than middle-aged adults?
It is because adults acquire immunity
• Some white blood cells, called T cells and B
cells have MEMORY for invaders they’ve
encountered before….
• They can detect a previous invader
(bacterium) and “jumpstart” an immune
response to it.
Adaptive Immunity
• Comprised of lymphocytes, macrophages, and
antibodies---- all very specific!!!!
Humoral (antibody) response
• Antibodies (orange) are attacking specific
antigens on cells
The Adaptive Immune system consists of
white blood cells, antibodies, and lymphatic
tissues
.
Two types of lymph tissue
• central lymphoid tissue (bone marrow, thymus)
and…..
• peripheral lymphoid tissue (lymph nodes,
spleen, mucosa-associated lymphoid tissue):
Types of white blood cells
in innate immunity
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•
•
•
•
1.
2.
3.
4.
4.
phagocytes (neutrophils, macrophages)
mast cells- skin, lungs, GI tract
NK cell
Basophils
Eosinophils
Natural Killer (NK) cells
Neutrophil,
eosinophil
Cells of Inflammation
The hallmarks of Adaptive Immunity
are specificity
and memory
• Specificity: the ability to recognize a particular
substance
• Memory: the ability to remember PREVIOUS
encounters with a particular substance
What’s Going On?
It all starts with a foreign antigen….
• The immune response starts with an antigen
approaching a cell of the immune system, a
dendritic cell or macrophage
Substances that stimulate
Adaptive Immunity are called
antigens
Foreign antigen: molecule introduced into
body
Self antigen: molecule produced by one’s
own body
Antigens
• Stimulate the production of antibodies
• Examples: A,B blood proteins
Other antigens
• pollen, animal hairs, foods, microorganisms..
or proteins on the cell membranes of
microorganisms
Antibodies
• Proteins found in plasma
• produced by B lymphocytes
• Part of “humoral immunity”
Antigen-antibody reaction
• When a foreign antigen enters the body, an
antibody is produced and “clumping” occurs
Cells of Adaptive immunity
B lymphocytes
T lymphoctyes
Dendritic cell
B cells vs. T cells
• Both are types of LYMPHOCYTES (made in
red bone marrow, travel to lymph tissue)
• T cells: cell-mediated immunity
• B cells: antibody-mediated immunity
The macrophage engulfs the antigen
by phagocytosis
foreign antigen
Lysosome with
enzymes
Antigen Processing
The vesicle containing an antigen fuses with a
lysosome. The enzymes in the lysozome break
down the antigen into fragments.
This is called “antigen processing”
Processed antigens move to cell
surface
enzymes and
proteins combining
Inside the macrophage,
the processed antigens
combine with special
class II MHC proteins.
These proteins can move
to the cell surface
membrane.
Class II
MHC proteins
Antigen-MHC complex
The antigen/MHC protein complex is
“presented” on the immune cell surface
membrane.
Cell-mediated immunity:
Antigen-presenting cell presents a
foreign antigen to a lymphocyte
Antigen-presenting cells: dendritic
cells
Dendritic cell
Once a dendritic cell phagocytizes a cell, it places some of its
proteins, called epitopes, on its surface—much like a fighter plane
displaying its hits. These surface markers serve as an alarm to
other immune cells. All cells that do this are called antigen
presenting cells (APCs).
•
Cell-Mediated Immunity
• 1. An MHC molecule displays a foreign
antigen (viral coat protein) on the surface of a
macrophage
• 2. Helper T-cell receptor binds to MHC
molecule/antigen complex
• 3. Cytotoxic T cell activated
• 4. Co-stimulation by cytokines (interleukin),
released by Helper T cell
• 5. More Cytotoxic T cells, memory T cells
produced
The Cascade Effect
Antibody-mediated immunity:
• 1. An MHC molecule displays a foreign antigen (viral
coat protein) on the surface of a macrophage
• 2. Helper T-cell receptor binds to MHC
molecule/antigen complex
• 3. B cells activated.
• 4. B cells divide and produce a clone of B cells,
specific to a particular foreign antigen
What’s happening here?
You are a clinical researcher. You want
to make a drug which will increase the
number of antibodies made to a
particular antigen in a group of
patients.
What could you do?
How could you decrease the
number of antibodies made to a
particular antigen?
A person who had the chicken pox as a
child becomes immune to the virus
Is this an example of innate or adaptive immunity?
What makes you say that?