1 introduction to immune system
DESCRIPTION
immuneTRANSCRIPT
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Prof Ammu K. Radhakrishnan FOUNDATION (Medical)
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Learning Outcomes:
You will be able to:
1. describe the functions of the immune
system
2. name the cells of the immune system
3. describe the types of immune
responses that protect host from
infections
4. discuss the different types of
immunity with examples
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Immune System
A body system that can
recognise and dispose
foreign/non-self
Microorganisms
Proteins
Organs/tissues
Other material
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Immune System
The body system that
1. protects host from infections
2. helps host to fight/recover from
infections
3. prevent recurrent infections
4. helps host in healing
5. protects host from cancers
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Immune System: Functions
1. Defence against infections
recognise & destroy harmful
micro-organism
provide long-term protection
against recurrent infections
2. Defence against tumours/
cancers
3. Key role in inflammation,
recovery & healing 24 October 2013
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Immune System
A complex body system
Involve many types of:
Cells Molecules
Soluble proteins
Organs Lymphoid organs and tissues
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Immune System: Main
Components
Cells
White blood cells
Leucocytes
Soluble defense proteins
Antibodies
Cytokines
Complement proteins
Others
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Immune System
Deals with microorganisms and
substances that are VERY
SMALL
How “Small is Small”?
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How Small is Small? Germs and the
Immune System: Getting a Sense of
Scale…
Picture the flat end of a pin, that
is about 1 mm across.
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1 mm
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How Small is Small? Germs and the
Immune System: Getting a Sense of
Scale…
If we placed some bacteria-
eating leucocytes end-to-end
across the flat end of a pin
would have room for 50
leucocytes in a line
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How Small is Small? Germs and the
Immune System: Getting a sense of
Scale…
If we did the same for a typical
bacterium
we would have room for 500
bacteria in a line!
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How Small is Small? Germs and the
Immune System: Getting a sense of
Scale…
If we did the same again for a
typical virus
we would have room for 10,000
viruses in a line!
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How Small is Small? Germs and the
Immune System: Getting a sense of
Scale…
If we did the same yet again for
an antibody molecule
we would find room for perhaps
100,000 antibody molecules in a
line
that stretched for just 1 mm!
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Phagocyte (WBC) > Bacteria >
Virus > Antibody
All very small
Invisible to the human eye!
How Small is Small? Germs and the
Immune System: Getting a sense of
Scale…
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Edward Jenner (1749-1823)
Noticed that:
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1
• An attack of smallpox protected against further smallpox disease
2
• Milkmaids who recovered from cowpox were protected from smallpox
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Immunisation: Live Microbes
Daring experiment!
Idea of using cowpox
virus to induce
“protection”
(immunity) to
smallpox
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Immunisation: Live Microbes
May 1796
inoculated an
8-year old
boy with
cowpox virus
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Immunisation: Live Microbes
The boy went
through the
normal
course of
cowpox
disease
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Immunisation: Live Microbes
July 1796
Inoculated the
same boy with
small pox
Child did not get
Smallpox! 24 October 2013
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Immunisation: Live Microbes
First demonstration of using a live not-so virulent form of micro-organisms
To protect against live, virulent form of the same/similar micro-organism
Pathogens shared some structural similarities
“cross-reactivity”
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Louis Pasteur (1888)
Studied the
pathogenesis of
cholera infection
in chicken
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Immunisation: Attenuated
Microbes
Live,
fresh
cholera
culture
DEAD 24 October 2013
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Immunisation: Attenuated
Microbes
Dead/weak
“old” cholera
culture
ALIVE ! 24 October 2013
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Immunisation: Attenuated
Microbes
ALIVE ALIVE
1. Inject dead, old
cholera
2. Inject live,
fresh cholera
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Immunisation: Attenuated
Microbes
First demonstration of using a weakened micro-organisms
to protect against live, virulent form of the same micro-organism
Attenuated micro-organism
usually alive but greatly weakened
virulence & pathogenicity
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Vaccinations
Immunisation
Many successful vaccinations
were demonstrated
In 18-19th century
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Defense Mechanisms
•Non-specific
•Natural/Native
•Specific
•Acquired
Innate Immune
Responses
Adaptive Immune
Responses
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Innate Immune Response:
General Characteristics
A type of host defense that is always present in healthy individual
Provides the initial protection against infections
1. Block entry of microbes
2. Rapidly eliminate microbe that enter host
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Innate Immune Response:
General Characteristics
Can effectively combat many
infections
Some pathogens have evolved
to resist innate immunity
Need to activate adaptive
immune response
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Adaptive Immune Response: Key
Characteristics
Host defense that is stimulated
by microbes that has invaded
the tissues
Develops more slowly and later
Mediates a more effective
defense against infections
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Invasion by Pathogens
Innate
defense mechanism
Adaptive
defense mechanism
Barriers
Skin
mucous lining
Acid & Enzymes
Inflammation
Phagocytes
Interferon
Complement
Antibody-
mediated
Cell-
mediated
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Immune System
Useful Terminology
Self and non-self
Antigen
Epitope
Antibody/immunoglobulin
Immunity
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What is “SELF”?
NORMAL
CONDITIONS
everything that
is coded within the
genome of an organism
IT IS IN THE GENES!
Rule does
not apply to
autoimmune
conditions
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What is “NON-SELF”?
Not coded for by the self
genome
Examples:
1. harmful micro-organisms
2. foreign proteins
3. transplant organs/tissues
4. incompatible blood transfusions
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Antigens
Substances that can trigger the adaptive arm of the immune system
E.g.
1. Foreign proteins, cells
2. Pathogens
E.g. Bacteria, Virus, Fungus, parasitic worms
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Antigen (Ag)
Substances recognised by:
1. Specific receptors on surface of B- or T- lymphocytes
T-cell receptors (TCR)
B-cell receptors (BCR)
2. Antibody/Immunoglobulin (Ig)
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Epitopes
Antigenic determinants
Areas exposed on antigens
that are recognised by:
1. Antibody (Ig)
2. Lymphocyte receptors (TCR,
BCR)
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Epitopes
Antigen
4 possible
Epitopes 1
2 4
3
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Immunodominant Epitope
The epitope on an antigen to
which there is the highest
immune response to
Useful in the design and
development of recombinant
vaccines
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Immunoglobulin (Ig)
Also known as antibody (Ab)
Defense glycopproteins in
plasma
Produced by Plasma cells
B-lymphocytes will differentiate
into plasma cells when activated
by specific antigens
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Immunoglobulin (Ig): Basic
Structure
Fc Region
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Immunoglobulin (Ig): Classes
5 classes of antibodies
1. IgG
2. IgA
3. IgM
4. IgE
5. IgD
Based on genes utilised
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IMMUNITY
Latin word “immunitas” which
means “Protection”
Does not refer to type of immune
response
There are two types of
protections
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IMMUNITY
PASSIVE ACTIVE
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Passive Immunity
A type of protection that does
not require activation of host’s
immune system
Host immune system is not
activated
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Passive Immunity
How is protection conferred to
individuals?
Transfer of lymphocytes or
antibodies from another
individual who is immune to a
naïve individual
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Passive Immunity
Limited period of protection
Depends on lifetime of transferred lymphocytes or antibodies
Short-lived
Used for rapidly conferring immunity even before individual is able to mount an active immune response
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Passive Immunity: Examples
1. Anti-Rhesus; anti-toxin, anti-
venom,
2. Maternal IgG that crosses the
placenta to the foetus
3. IgA from mother’s milk
Colostrum
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Active Immunity
Requires activation of host’s
immune system
Produce long-lived memory
cells
Those who recover from some
epidemic or infectious diseases
were exempt from further attacks
Long-lived immunity/protection
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Active Immunity: Examples
1. Recovery from infections
2. Vaccinations
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Types of Immune Responses
Blood consist of:
Fluid part (plasma)
Living cells (cells)
Early 18-19th
debates about which component of blood is responsible for the immune response
Cells or fluid?
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Adaptive Immune Response
Antibody (Humoral)
Extracellular microbes/antigens
Cell-mediated
Intracellular microbes/antigens
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Immune Response
Cell-mediated Humoral
Involve
Leucocytes Antibodies
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Humoral Immune Response
Mediated by soluble proteins
called antibodies
Produced by activated B-
lymphocytes
Plasma cells
Antibodies are secreted into
circulation and mucosal fluids
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Antibodies
Neutralise and eliminate microbes & microbial toxins in
blood
lumens of mucosal organs
Prevent microbes present on mucosal surfaces/blood from colonising host cells/organs
Prevent establishment of infection
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Antibodies
Do not have access to microbes
that live and divide inside
infected cells
Intracellular microbes
Require cell-mediated immune
response to eliminate these
microbes
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Cell-Mediated Immune
Response
Defense against intracellular
microbes
Mediated by T-lymphocytes
2 main types:
1. Activating phagocytes to
destroy and ingested microbes
2. Directly kill infected host cells
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CONSEQUENCES OF IMMUNITY
DESIRABLE UNDESIRABLE
1. Natural resistance
against pathogens
2. Recover from
infection
3. Acquire immunity
to infectious
agents
1. Allergy &
Hypersensitivity
2. Autoimmune
diseases
3. Rejection of
organ
transplants
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