Download The Immune System

Biology Today (BIOL 109)
Talk Twelve:
The Immune System
Chapter 20
The Immune System
• Immunity is the ability to react to
antigens so that the body remains
free of disease.
– Disease is a state of homeostatic
imbalance.
• Can be due to infection or failure of the
immune system.
Primary Lymphatic Organs
• Lymphatic organs
contain large numbers of
lymphocytes (White
Blood cells).
• Primary organs are:– Red Bone Marrow.
• Site of stem cells.
– Source of B lymphocytes.
– Thymus Gland.
Lymphocytes from bone
marrow pass through to
form T-lymphocytes
• Produces thymic hormones
(thymosin).
• Aids in T lymphocyte
maturation.
Secondary Lymphatic Organs
• Secondary lymphatic organs are
places where lymphocytes encounter
and bind with antigens.
–
–
–
–
Spleen.
Lymph nodes.
Tonsils.
Peyer’s patches.
Lymphatic Organs
Secondary Lymphatic Organs
• Spleen – upper left of
abdominal cavity behind
stomach. Sectioned off by
connective tissue- white
pulp & red pulp.
– White pulp – lymphocytes
– Red pulp – filters blood.
Blood entering the spleen
passes through red pulp
before it leaves (network
of sinuses)
– FRAGILE
Secondary Lymphatic Organs
• Lymph Nodes – occur along
lymphatic vessels. Formed
from connective tissue.
– Packed full of Blymphocytes
– As lymph courses through
sinuses it is filtered by
macrophages, which
engulf pathogens and
debris.
– Also present- Tlymphocytes – fight
infection and attack
cancer cells
Secondary Lymphatic Organs
• Tonsils – patches of
lymphatic tissue.
• Perform the same
function as lymph nodes
– First line of defense
• Peyer’s Patches – on
the intestinal wall and
appendix. Attack
pathogens that ender
the body by way of the
intestinal tract.
Nonspecific Defenses
• Barriers to Entry.
– Mucous membranes
• Line respiratory, digestive, and urinary tract.
– Oil gland secretions.
• Chemicals that kill or weaken bacteria on
skin
– Ciliated cells.
• Sweep mucus & particles into throat
– Bacteria
• Both in stomach and vagina, prevent
pathogens from gaining a foot-hold.
– Acid
Innate Immunity
• One important function of the immune system is to
promote growth and repair after injury
– Either via physical damage or microorganisms
• The mobilization of innate immune cells to get rid
of damaged cells or microorganisms is called
inflammation
• Small molecules called cytokines are also involved
Innate Immunity
• Inflammatory Reaction.
– Tissue damage causes
– tissue cells and mast cells to release chemical
mediators.
Innate Immunity
• Inflammatory Reaction.
• Histamine and kinins.
– Capillaries dilate and become more permeable.
» Skin reddens and becomes warm.
– Proteins and fluids escape from tissue. Swelling
occurs
Innate Immunity
• Inflammatory Reaction.
– Proteins and fluids escape from tissue and cause
swelling.
» Swelling stimulates free nerve endings, causing
the sensation of pain.
Innate Immunity
– Neutrophils and
Monocytes migrate to
site of injury.
– Amoeboid – can change
shape – squeeze
through capillary walls
and enter tissue fluid.
– Neutrophils engulf
pathogens –destroyed
by hydrolytic enzymes
when fused to a
lysosome
Innate Immunity
• Macrophages:
Monocytes change into
these as they leave
the blood and enter
the tissues.
– These are phagocytic
cells
– Can eat many (100’s) of
pathogens and survive.
– Eat old blood cells and
bits of dead tissue
– Stimulate the immune
response.
• Increase production of
white blood cells in bone
marrow.
Innate Immunity
• Macrophages:
Monocytes change into
these as they leave
the blood and enter
the tissues.
• Macrophages enter
lymph vessels carring
bacteria fragments to
lymph nodes
• This starts a specific
immune response
Protective protein system
• Known as Complement proteins
• Are activated when pathogens enter the body.
• Complement certain immune responses.
Protective protein system
• Attract phagocytes.
• Form holes in bacteria.
• Interferon binds to receptors of non-infected cells
causing them to prepare for possible attack
Specific immunity
• Antigen--shape on cell, allows recognition of
self and detection of foreign cells.
• Antibody--protein that recognizes and binds
antigens.
• Specific defenses respond to antigens.
– Lymphocytes recognize an antigen due to antigen
receptors whose shape allows them to combine
with a specific antigen.
• Immunity is primarily the result of the action of B
lymphocytes and T lymphocytes.
White blood cells
• Granular Leukocytes
– Neutrophils: Most abundant. Have multilobed
nucleus.
• They are the first to respond to infection, and engulf
pathogens during phagocytosis.
– Eosinophils: Have bilobed nucleus
• Known to increase in number in the event of parasitic
worm infection and during allergic reaction.
– Basophils: U-shaped or lobed nucleus.
• In connective tissues release histamines along with
Mast Cells
White Blood Cells
• Agranular Leukocyles
– Monocyles: Largest of the white blood cells.
• Differentiate into even larger Macrophages
• Phagocytize pathogens, old cells and debris
• Stimulate production of other white blood cells
– Lymphocytes: Two types:
• T-lymphocytes – Destroy any cell with foreign antigens
• B-lymphocytes – Produce antibodies that combine with
antigens
– Target pathogens for destruction
Natural Killer Cells
• Natural killer cells kill
virus-infected cells
and tumor cells by
cell-to-cell contact.
– Large, granular
lymphocytes.
T Cells
• Provide cell-mediated immunity.
• Produced in bone marrow, mature in
thymus.
• Antigen must be presented in groove of
HLA molecule.
• Cytotoxic T cells destroy non-self
protein-bearing cells.
• Helper T cells secrete cytokines that
control the immune response.
B Cells
• Provide antibody-mediated immunity against
bacteria.
• Produced and mature in bone marrow.
• Reside in spleen and lymph nodes.
– Circulate in blood and lymph.
• Directly recognize antigen and then undergo
clonal selection.
• Clonal expansion produces antibodysecreting plasma cells and memory B cells.
Clonal selection Theory
• The antigen selects which
lymphocyte will undergo
clonal expansion and produce
more lymphocytes with the
same type of antigen
receptor.
– Some become memory cells –
long term immunity to the same
infection.
– B-cells become plasma cells –
fight infection
– Apoptosis – when danger of
infection is over, all plasma
cells undergo programmed cell
death
Specific Defenses
– Antibodies are
proteins shaped like
an antigen receptor
and capable of
combining with, and
neutralizing, a
specific antigen.
• Classes.
–
–
–
–
–
Antibodies
IgG - Enhances phagocytosis.
IgM - Activates complement proteins.
IgA - Prevents attachment of pathogens.
IgD - Antigen receptors on virgin B cells.
IgE - Immediate allergic response.
Induced Immunity
• Active Immunity.
– Immunization involves
use of vaccines.
– Contain an antigen to
which the immune
system responds.
– Primary
response.
Secondary
(booster)
response.
– Dependent upon the
presence of memory B
and T cells capable of
responding to lower
antigen doses.
Induced Immunity
• Passive immunity
• occurs when an
individual is given
prepared antibodies.
– Temporary.
• No memory cells.
• Primary and
secondary
injections
Issue - Allergies
• Occurs when your immune system reacts atypically
to some antigens to which the host does not need
protection.
• Pollen, dust mites, cats, a hard days work!
– Called Allergens
• The atypical response produces a special antibody
– IgE
• A form of innate immunity
Allergies
• IgE binds to mast cells.
•
When a person later
encounters the same
allergen, the allergen binds
to the IgE on the mast cell
• This triggers the explosive
release of histamine
• Capillaries dilate and
become more permeable.
• Skin reddens and becomes
warm. Proteins and fluids
escape from tissue.
Swelling occurs
–
Allergies
• The large amounts of
histamines released in an
allergic reaction cause
strong symptoms
• Runny eyes, sneezing, or
shortness of breath
• Depends upon the tissue in
which the mast cells were
triggered
Allergies
• As allergy symptoms are caused by histamines,
taking antihistamines stops the build up of
histamines in the cells of blood vessels.
• However, antihistamines do not stop the immune
response or the release of histamines in mast cells
• Other allergies are mediated by T-cells
– Latex, poison ivy, dyes or chemicals in cosmetics or
clothing
– Antihistamines do not help in these allergic reactions
Allergies
• As each allergy is an antigen-specific immune
response it shows memory and a greater response
on the next exposure
– This is why allergies get worse over time
• Thousands of different substances can produce
allergies in people – each triggered by a specific
antigen-specific response
– Why people are usually bothered by only a few
• Appears to be inherited
– Remember human genetics and meiosis!!!!
The End.
Any Questions?