Download Specific resistance to infection

Human Biology ATAR & General Unit 3
Keywords
 Pathogen
 Antigen
 Lymphatic system
 Lymph node
 Long bond
 B-cells
 Plasma cell
 Memory B cell
 Antibodies
 T-cells
 bone marrow
 Specific immunity
 Humoral reponse
 Antibody mediated immunity
 Cellular response
 Cell mediated immunity
 Macrophage
 Phagocytosis
Helper T cell
Killer T cell
Suppressor T cell
Memory T cell
Cytokines
Primary response
Secondary response
Immunity
 Passive immunity
 Active immunity
Vaccination
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 Lymphocyte
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Immune system
The immune system involves:
 Lymphatic system
 Lymph nodes
 Thymus
 Spleen
 Long bones
 Bone marrow
The main types of white blood
cells involved:
 Macrophages
 Lymphocytes
Leucocytes:
lymphocytes & macrophages
 Both macrophages and lymphocytes are types of
leucocytes (white blood cells)
 Macrophages engulf pathogens to destroy them
(phagocytosis)
 Lymphocytes are produced in the lymph nodes
 Both are able to leave the blood stream and lymph
vessels to enter the tissues in search of pathogens
The immune response
The immune response is a homeostatic mechanism.
There are 3 parts to the immune response:
1.
The humoral response
involves the production
of special proteins
called antibodies.
It is also called
antibody-mediated
immunity
2. The cell mediated
response involves the
formation of special
lymphocytes that
destroy invading
agents
3. Macrophages are involved in phagocytosis and work
alongside the humoral and cell mediated responses
The lymphatic system
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All three aspects of the immune response involve
lymphoid tissue
Much of the lymphoid tissue is composed of 2 types
of lymphocytes:
B cells which provide antibody-mediated immunity
(matured in the bone marrow)
T cells which provide cell-mediated immunity
(matured in the thymus)
Blood
capillary
Lymph capillary
Lymph & blood
vessels
 The lymphatic and
circulatory
systems are closely
connected
 Their proximity
allows leucocytes
to easily travel
from the lymph
fluid to the blood
and back again
Section through a lymph node
Efferent lymph
vessels
Cortex
(T cells)
Medulla
(macrophages)
Germinal centre
(B cells)
Afferent lymph vessels
The Miles Kelly Art library, Wellcome Images
Antigens and antibodies
 The body produces self antigens that are unique to
each individual.
 A non-self antigen is a foreign substance that enters
the body. It will trigger a specific immune response
 These non-self antigens could be:
 Proteins, carbohydrates, lipids, nucleic acids
 Viruses
 Bacteria and other micro-organisms
 Pollen grains, tissues transplanted from another
person, dust particles
Antigens and antibodies
 An antibody is a specialised protein
that is produced in response to an
antigen
 It belongs to a group of proteins
called immunoglobulins (Ig)
 Each antibody is specific for an
antigen
 They fit together like a lock and
key, forming an antigen-antibody
complex
Antigen-antibody
complex
Antibody mediated immunity
 Involves B-cells
 Produce antibodies
 Each B-cell is specific for
an antigen
 Therefore there are many
different types of B-cells
in the body
Antibody mediated immunity
Steps
1. An antigen comes into contact with a B-cell and the Bcell becomes activated
2. The B-cell enlarges and divides into a group of cells called
a clone
3. Most of the clone cells become plasma cells
4. The plasma cells secrete the specific antibody capable of
attaching to the active site of the antigen
5. The B cells of the clone that did not differentiate into
plasma cells remain as memory cells
6. These memory cells spread to all the body tissues to allow
the response to occur more rapidly next time
How antibodies work
Antibodies may:
 Inactivate foreign enzymes or toxins by binding with
them
 Bind to viruses to prevent them from entering cells
 Cause antigens to clump together (agglutination)
 Dissolve micro-organisms
 Make antigens more easily consumed by
macrophages by:
 Coating bacteria
 Making soluble substances insoluble
Cell-mediated immunity
 Involves T cells
 Provides resistance to the intracellular phase
of bacterial and viral infections
 The intracellular phase is when the pathogen
uses the host’s own cells to replicate. This occurs
with viral infections
 There are thousands of different types of T cells
Cell-mediated response
Steps
1. When a non-self antigen enters the body, the
corresponding T-cell becomes sensitised
2. This sensitisation occurs after a B-cell or a
macrophage encounters the foreign antigen, travels
to the nearest lymph node and presents it to the Tcell
3. The sensitised T-cells enlarge and divide, each giving
rise to a clone
4. Some cells remain in the lymphoid tissue as memory
cells
Cell-mediated immunity
5. The T cells that do not become memory cells develop
further into:
 Killer T cells
 Helper T cells
 Suppressor T cells
Killer T-cells
Killer T cells
 Killer T cells migrate to
the site of infection and
attach themselves to the
invading cells
 They secrete a substance
that destroys the antigen
Helper T-cells
 Helper T cells play a role
in both humoral and
cellular immunity by
secreting substances
(cytokines) that help
the immune response
 Sensitise T-cells
 Attract macrophages
(chemotaxis)
 Increase the phagocytic
activity of macrophages
Suppressor T-cells
 Suppressor T-cells act
when the immune
activity becomes
excessive or when the
infection has been dealt
with
 They release substances
that inhibit the activity
of T and B cells
B cells
T cells
Antibody mediated immunity Cell mediated immunity
Chemical-based system
Cell-based system
Produce antibodies (Ig)
Produce killer cells, helper
cells, suppressor cells
Lymphocytes matured in
bone marrow
Lymphocytes matured in
thymus
Effective against
extracellular bacteria
Effective against intracellular
viruses & cancer cells
Antibody mediated immunity
1. Pathogen
displaying
antigens
2. Antigen recognised
by compatible antibody
6. Cytokines cause B
cell to mature into
plasma cell
7. Plasma cell
secretes antibody
3. B cell digests antigen &
displays antigen fragments
T
helper
cell
B cell
4. Helper T cell
recognises
antigen
5. Activated Helper
T cell releases
cytokines
Cell mediated immunity
1. Pathogen
ingested by
macrophage cell
Memory
T cell
4. Cytokines
stimulate killer T
cells to divide
Killer
T cell
Helper
T cell
2. Pathogen digested &
fragments presented to
T cells
B cell
Killer
T cell
3. Helper T
cells secrete
cytokines
Helper
T cell
Cytokines activate B
pathway
5. Killer T cells
hunt and destroy
infected cells
Primary & secondary response
 The immune response on first exposure to an antigen
is called the primary response
 During this time the body’s immune system responds
fairly slowly, taking a few days to build up large
amounts of antibodies
 The primary response leaves the immune system with
a memory of that particular antigen
Primary & secondary response
 With a subsequent exposure to the same antigen, the
response is much faster because of the mem0ry cells
 With a secondary response, plasma cells are able to
form very quickly
 The secondary response is a rapid response to the
invading pathogen
Primary & secondary responses
Types of immunity
 Immunity is resistance to
infection by invading
micro-organisms
 Natural immunity occurs
without any human
intervention
 Artificial immunity
results from giving people
an antibody or antigen
 Both natural and artificial
immunity can be either
passive or active
Passive immunity
 Passive immunity is when a person is given antibodies
produced by someone else.
 This can occur naturally (ie mother and baby through
placenta or breast milk)
 It can also be artificial, such as when a person is injected
with antibodies to combat a particular infection
 Passive immunity is short term - it only lasts until the
antibodies are broken down. The body doesn’t produce
memory cells
Types of immunity
 Active immunity results when the body is exposed to
a foreign antigen and manufactures antibodies in
response to that antigen
 It can be naturally induced, eg. when you are exposed
to a virus
 It can be artificially induces eg. Vaccination
 This type of immunity lasts long-term because it
produces memory cells
Passive immunity
Natural
Exposure
Effects
Immune
response
Antibody enters
baby via placenta
or breast milk
Baby does not get
ill - obtains
immediate, shortterm protection
Baby does not
acquire immunity
– will get ill on
subsequent
exposure
Person does not
get ill - obtains
immediate, shortterm protection
Person does not
acquire immunity
– will get ill on
subsequent
exposure
Artificial Serum
Active immunity
Exposure
Dosage
Effects
Immune
response
Natural
Active
pathogen
Very small
amount
Person gets
ill
Acquires
active
immunity
Artificial
Dead or
altered
pathogen
= vaccine
Very large
amount
Person does Acquires
not get ill
active
immunity
Crash Course
 Immune system (15 minutes)
https://www.youtube.com/watch?v=CeVtPDjJBPU
Vaccines
 Immunisation means programming the immune
system so that the body can respond rapidly to
infection
 Vaccination is the artificial introduction of antigens
of pathogenic organisms so that the ability to produce
the appropriate antibodies is acquired without the
person have to suffer the disease
 A vaccine is the antigen preparation used in artificial
immunisation
Type of vaccine
Components
Example
Living attenuated
micro-organisms
Contains live micro- Measles, mumps,
organisms with
rubella
reduced virulence
Dead microorganisms
Contains whole
dead microorganisms
Cholera, whooping
chough
Toxoids
Contains toxins
Diphtheria, tetanus
Subunit vaccines
Contains fragments
of the microorganism eg.
Hepatitis B
Vaccines
 Modern vaccines use recombinant DNA
techniques
to produce less virulent strains
to insert certain DNA segments from the
pathogen into a harmless bacteria, so that the
harmless bacteria produces antigens that are
characteristic of the pathogen.
Vaccine delivery