Immune Defense against Disease
What is an infectious disease?
Disease-producing agents
such as bacteria,
protozoans, fungi, viruses,
and other parasites are
called pathogens. (NOT all
microorganisms are
pathogens)
Main sources of
pathogens are soil,
contaminated water, and
infected animals, including
other people.
Reservoirs of pathogens
Pathogens are some causes of infectious diseases.
Transmission of disease
• Pathogens can be transmitted to a host from
reservoirs in four main ways: by direct contact, by an
object, through the air, or by an intermediate
organism called a vector.
Transmission of disease II
• The common cold,
influenza, and STDs are
spread by direct
contact.
Transmission of disease III
• Bacteria and other
microorganisms can be
present on nonliving
objects such as money,
toys, or towels.
• Transmission occurs
when people
unknowingly handle
contaminated objects.
Transmission of disease IV
• Airborne transmission of a disease can occur when a
person coughs or sneezes, spreading pathogens
contained in droplets of mucus into the air.
Transmission of disease V
Diseases transmitted by vectors
are most commonly spread by
insects and arthropods.
Malaria and the West Nile virus
are transmitted by mosquitoes.
Lyme disease and Rocky
Mountain spotted fever are
diseases that are transmitted
by ticks.
Flies also are significant vectors
of disease.
What causes disease symptoms?
When a pathogen invades your body, it encounters
your immune system.
If the pathogen overcomes the defenses of your
immune system, it can metabolize and multiply, causing
damage to the tissues it has invaded, and even killing
host cells.
Host damage by viruses and bacteria
Viruses - are they alive?
Viruses are exceptions to the cell theory
A virus is not a cell. Viruses are made of two chemicals,
protein & nucleic acid, but have no membranes,
nucleus, or protoplasm
Viruses appear to be alive when they reproduce after
infecting a host cell
Host damage by viruses and bacteria
Most of the damage done to host cells by bacteria is
inflicted by poisonous toxins.
These toxins can inhibit protein synthesis in the host
cell, destroy blood cells and blood vessels, produce
fever, or cause spasms by disrupting the nervous
system.
Patterns of Diseases
Some diseases, such as typhoid fever, occur only
occasionally in the United States.
On the other hand, many diseases are constantly
present in the population-endemic disease. (Ex., the
Common cold, rhinoviruses)
Treating Diseases
1 Way -Treating diseases with antibiotics:
An antibiotic is a substance produced by a
microorganism that, in small amounts, will kill or
inhibit the growth and reproduction of bacteria.
Note that antibiotics have NO impact
on viruses, only bacteria!
Your body also has its own built-in multi-layer defense
system— the immune system —that works to keep you
healthy.
Lines of defense
• 1st line: Barrier defense
– broad, external defense
• “walls & moats”
– skin & mucus membranes
• 2nd line: Non-specific defense
– broad, internal defense
• “patrolling soldiers”
–phagocyte (eating) WBCs
Lines of defense
• 3rd line: Immune System Action
– specific, acquired immunity
• “elite trained units”
– lymphocyte WBCs & antibodies
• B & T cells
Innate Immunity
The body’s earliest lines of defense against any and all
pathogens make up your nonspecific, innate immunity.
Nonspecific defense 1
Lining of
1st line of defense:
trachea:
Skin Intact skin is a
ciliated cells
formidable physical
& mucus
barrier to the entrance secreting
of microorganisms
cells
Nonspecific defense 1
1st line of defense:
Body secretions mucus
traps many
microorganisms.
Sweat, tears, and saliva
all contain the enzyme
lysozyme, which is
capable of breaking
down the cell walls of
some bacteria.
Nonspecific defense 2
2nd line of defense:
Inflammation(Inflammatory response) characterized by
four symptoms—redness, swelling, pain, and heat;
histamine released causes blood vessels in the injured
area to dilate,(redness) which makes them more
permeable to tissue fluid. Fluid that leaks from the
vessels helps the body destroy toxic agents and restore
homeostasis (swelling, pain, & heat)
Nonspecific defense 2
2nd
line of defense:
After a few days, infected
tissue harbors a collection
of live and dead white
blood cells, multiplying and
dead pathogens, and body
fluids called pus.
Pus formation usually
continues until the infection
subsides.
Eventually, the pus is
cleared away by
macrophages.
Swelling
occurs
Tissue fluid moves
into injured area
Pus
Phagocytes
Nonspecific defense 2: Fever
2nd line of defense:
When a local response is not enough a
full body response to infection raises
body temperature.
The higher temperature helps in
defense as it slows growth of
pathogens, helps macrophages, and
speeds up repair of tissues.
Nonspecific defense 3
2nd line of defense:
Phagocytosis of
pathogens - white
blood cells that destroy
entire pathogens by
surrounding and
engulfing them.
Macrophages are white
blood cells that provide
the first defense against
pathogens that have
managed to enter the
tissues.
Macrophage “eating” bacteria
Phagocytes
macrophage
bacteria
white blood cells that eat
macrophage
yeast
Nonspecific defense 4
2nd line of defense:
Phagocytosis of pathogens
If the infection is not stopped by the tissue
macrophages, another type of phagocyte, called a
neutrophil, is attracted to the site.
If the infection is not stopped by tissue
macrophages and neutrophils – then Monocytes
are introduced.
Nonspecific defense 5
2nd line of defense:
Protective proteins
Interferon is a group of proteins that protect cells
from viruses.
Complement: help attract phagocytes to foreign
cells and help destroy foreign cells.
Natural Killer cells: type of white blood cell that
destroy the body's own infected cells, and may
attack cells that form tumors.
Nonspecific defense 5
The lymphatic system
2nd line of defense:
The lymphatic system becomes a crucial
battleground during infection.
• It is a network of lymphatic vessels and organs.
• It returns tissue fluid to the circulatory system.
• It fights infections.
• Lymph nodes are key sites for fighting infection.
• They are packed with lymphocytes and
macrophages.
The lymphatic system
Acquired Immunity
• Acquired Immunity ≡ defending against a specific
pathogen by gradually building up a resistance to the
pathogen.
• This acquired immune response enables these white
blood cells to inactivate or destroy the pathogen.
• Acquired immunity involves the production of two
kinds of immune responses: antibody immunity and
cellular immunity:
• your 3rd line of defense
Acquired Immunity
3rd line of defense:
SPECIFIC IMMUNITY
– IMMUNE RESPONSE: a recognition system that
distinguishes “self” from “non-self”.
– responds to foreign molecules called antigens
– Stimulates the body to make antibodies:
• specific defensive proteins which help to
counter antigens in various ways.
How are invaders recognized?
• Antigens ≡ chemical name tags on the surface
of every cell
• Label all cells as “self” vs. “invader”
one of your
own cells
antigens say:
“I belong here”
disease-causing
virus
disease-causing
bacteria
antigens say:
“I am an invader”
antigens say:
“I am an invader”
Lymphocytes
3rd line of defense:
Lymphocyte ≡ type of white
blood cell that carry out the
immune response.
• Two kinds of lymphocyte:
– B cells secrete antibodies
that attack antigens
(antibody immunity)
– T cells attack cells
infected with pathogens
(cellular immunity)
B lymphocyte
B cells & antibodies
3rd line of defense:
• B cells
– white blood cells that attack
invaders in blood
– mature in Bone marrow
i. Patrolling B cells
• make antibodies against invader immediately
ii. Memory B cells
• remembers invader
• make antibodies quickly the next time; protects
you from getting same disease more than once
Antibodies
3rd line of defense:
• Antibodies ≡ Proteins made by B cells that tag invaders
in the blood so macrophages can eat them.
– tag says “this is an invader”  gotcha!
• biological “handcuffs”
– antibody attaches to antigen of invader
B cells releasing antibodies
Y
Y
Y
Y
Y
Y
Y
Invading germs tagged
with antibodies
Y
Y
Y
Y
Y
Y
macrophage
eating tagged invaders
Antibody Immunity
3rd line of defense:
• An antibody molecule
has antigen-binding sites
specific to the antigen.
• Antibodies do not
possess the power to
destroy antigens directly,
but antibodies tag and
identify antigen-marked
cells for destruction by a
variety of mechanisms.
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y Y
Y
Y
Y
Y
Y
Y
Y
“reserves”
Y Y
Y
Y
Y
10 to 17 days
Y
Y
Y
Y
Y
Y
Y
Y
memory B cells
Y
Y
Y
Y
Y
Y
Y
recognition
B cells
Y
release
antibodies
patrol blood
forever
Y
Y
Y
Y
Y
Y
Y
B cells
Y
(foreign antigen)
Y
Y
Y
invader
Y
Y
B cells immune response
Y
T cells
3rd line of defense:
• T cells mature in the Thymus
• Helper T cells
– sound the alarm for rest
of immune system
• Killer T cells
– destroy infected body cells
• Memory T cells
– remembers invader & reacts
against it again quickly
Where’s that?
Attack of the Killer T cells
3rd line of defense:
• Killer T cells destroy infected body cells
– T cell binds to invaded cell & secretes Perforin
• Perforin punctures cell membrane of infected cell
• cell bursts (lysis)
Killer T cell
vesicle
T-cell
membrane
Perforin:
punctures
invaded cell
membrane
I-cell
membrane
invaded cell
Cellular Immunity
Infected cells
Perforin
Pathogen
engulfed by
Displays antigens
on surface and
stimulates T cell
Foreign
antigen
Infected cell lyses
Cytotoxic T cell
Macrophage
Attacks infected
cell
Stimulates
Helper T cell
Cytotoxic T cell
Immune response
invader
skin
invaders in body
invaders in blood
skin
invaders infect cells
macrophages
helper
T cells
B cells
Y
Y
Y
Y
Y
Y
Y
memory
T cells
Y antibodies
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y antibodies
memory
B cells
Y
patrolling
B cells
T cells
killer
T cells
Passive and Active Immunity
Acquired immunity to a disease may be either passive
or active.
Passive Immunity
Passive immunity: short
term, antibodies passed
on, not stimulated by
antigens.
– acquired naturally by
placenta or breast
milk
– artificially acquired
by a vaccine
Active Immunity
Active: long term, conferred
by actual encounter with
infection (naturally
acquired) or vaccine
(artificially acquired).
• Vaccine≡ substance
consisting of weakened,
dead ,or parts of
pathogen or antigen that
when injected , stimulates
the immune system.
Noninfectious disorders
Genetic disorders
• Caused by the
inheritance of genes
that do not function
properly.
• ex: sickle cell
anemia, hemophilia,
cystic fibrosis
Noninfectious disorders
• Degenerative diseases≡
result of a part of the
body wearing out (ex:
degenerative arthritis)
• Metabolic diseases≡
results in an error in a
biochemical pathway
• Cancer≡ abnormal cell
growth
Immune System Disorders
Allergies are overreactions to
certain environmental
antigens called allergens (ex.
animal dander, dust mites,
pollen)
• The release of histamine
causes symptoms:
sneezing, increased mucus
production in the nasal
passages, and redness.
• Antihistamines can relieve
symptoms.
Immune System Disorders
Autoimmune diseases: the
immune system also can
mistakenly attack the
body’s own tissues.
(ex: Rheumatic fever,
Type I Diabetes,
Multiple Sclerosis,
Rheumatoid arthritis,
Lupus)
Rheumatoid arthritis
Immune System Disorders
HIV Replication
Immunodeficiency diseases:
• Immune components are
lacking, and infections
recur
• Ex: Acquired immune
deficiency syndrome
(AIDS)
– AIDS is result of HIV
infection; HIV is NOT
AIDS!
AIDS
• HIV (Human
Immunodeficiency
Virus); the virus that
causes AIDS.
• HIV is transmitted
mainly in blood and
semen.
• HIV kills helper T-cells
and can lead to AIDS.
Attacking transplanted tissue.
• T cells and antibodies also can attack transplanted
tissue, such as a transplanted organ, that comes from
a source outside new host body.
• Blood transfusions with wrong antigens (blood type)
are attacked, leading to clotting.