Transcript Immunity to Infection

Immunity to
Infection
Immunity to Infection
• Immunity is the acquired ability to defend
against infection by disease-causing
organisms.
• The adaptive immune system is
responsible for immunity.
How B-cells work…
Pathogen (e.g. bacteria, virus)
Macrophage
B-cells
Each recognise
a different
antigen. The
correct one
develops into…
Macrophage
Phagocytoses pathogen
and displays antigens on
surface
Plasma cells
Clones of the
correct B-cell,
which produce
antibodies
1st meeting a pathogen, this
process takes 10-14 days
Memory B cell= subesquent
meetings, takes about 5 days
Abnormal cell e.g
cancer cell, infected cell
Killer T-cell
recognises antigen
How T-cells work…
X
Antigen
Clones of killer T-cell
attach to antigen
Normal cell
X
Killer T-cells release
perforin pores
X
Helper T-cell stimulates
correct killer T-cell to
multiply
Helper T-cell also
stimulates B-cells
to make antibodies
Suppressor T-cells
turn off immune
response
Abnormal cell gains
water, swells and
bursts
Memory Tcells stay in
circulation
Types of Immunity
Active immunity
Passive immunity
Naturally acquired
Naturally acquired
Artificially acquired Artificially acquired
Types of Immunity
• Natural immunity is the result of a body’s
previous encounter with an organism.
• Artificial immunity results from the injection of a
vaccine or an antibody. Vaccines stimulate active
immunity whereas injection antibody or antiserum
is an example of passive immunity.
Types of Immunity
• Active immunity is when the immune system
encounters and antigen and is primed to
recognise it and destroy it quickly the next time it
is encountered. This is active immunity because
the body’s immune system prepares itself for
future challenges.
• Passive immunity is short-term and involves
the transfer of immunity from one individual
to another via antibody-rich serum. This may be
artificial as is the case with anti-venom or natural,
as in antibodies crossing the placenta to protect
the developing foetus.
Induced Immunity
Active immunity
Production of a person’s own
antibodies. Long lasting
Natural Active
Artificial Active
When pathogen
Vaccination – usually
enters body in the contains a safe antigen
normal way, we
from the pathogen.
make antibodies
Person makes
antibodies without
becoming ill
Edward Jenner
Passive immunity
An individual is given antibodies by another
Short-term resistance (weeks- 6months)
Natural Passive
Baby in utero
(placenta)
Breast-fed babies
Artificial Passive
Gamma globulin
injection
Extremely fast, but
short lived (e.g. snake
venom)
Vaccines
• The word vaccination comes from vacca, which is Latin for cow.
• Edward Jenner could be considered the “father of vaccination”
as he developed a method of protecting people from smallpox.
• He noticed that milkmaids who had previously been infected with
cowpox (similar disease but milder) did not catch smallpox.
• In 1796, Jenner deliberately infected a small boy with material
from a cowpox pustule, then six weeks later infected the boy
with material from a smallpox pustule. The boy survived!
• Our current understanding of pathogens indicates that Jenner
got lucky – not all dangerous diseases have a less pathogenic
equivalent as was the case with smallpox and cowpox.
Types of Vaccine
• There are four main types of vaccinations:
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Live attenuated vaccines
Killed vaccines
Toxoid vaccines
Component vaccines
• Many vaccines contain adjuvants. This is a
general term given to any substance that when
mixed with an injected immunogen will
increase the immune response. Examples of
adjuvants include aluminium hydroxide and
aluminium phosphate.
Live attenuated vaccines
•
Contain bacteria or viruses that have been altered so they can't cause
disease.
•
Usually created from the naturally occurring germ itself. The germs used in
these vaccines still can infect people, but they rarely cause serious disease.
•
Viruses are weakened (or attenuated) by growing them over and over again in
a laboratory under nourishing conditions called cell culture. The process of
growing a virus repeatedly-also known as passing--serves to lessen the
disease-causing ability of the virus. Vaccines are made from viruses whose
disease-causing ability has deteriorated from multiple passages.
•
Examples of live attenuated vaccines include:
– Measles vaccine (as found in the MMR vaccine)
– Mumps vaccine (MMR vaccine)
– Rubella (German measles) vaccine ( MMR vaccine)
– Oral polio vaccine (OPV)
– Varicella (chickenpox) vaccine
Killed vaccines
• Contain killed bacteria or inactivated viruses.
• Inactivated (killed) vaccines cannot cause an
infection, but they still can stimulate a protective
immune response. Viruses are inactivated with
chemicals such as formaldehyde.
• Examples of inactivated (killed) vaccines:
– Inactivated polio vaccine (IPV), which is the injected
form of the polio vaccine
– Inactivated influenza vaccine
Toxoid vaccines
• Contain toxins (or poisons) produced by the germ that
have been made harmless.
• Toxoid vaccines are made by treating toxins (or poisons)
produced by germs with heat or chemicals, such as
formalin, to destroy their ability to cause illness. Even
though toxoids do not cause disease, they stimulate the
body to produce protective immunity just like the germs'
natural toxins.
• Examples of toxoid vaccines:
– Diphtheria toxoid vaccine (may be given alone or as one of the
components in the DTP, DTaP, or dT vaccines)
– Tetanus toxoid vaccine (may be given alone or as part of DTP,
DTaP, or dT)
Component vaccines
• Contain parts of the whole bacteria or viruses.
• These vaccines cannot cause disease as they contain only parts of
the viruses or bacteria, but they can stimulate the body to produce
an immune response that protects against infection with the whole
germ.
• Component vaccines have become more common with the advent
of gene technology, as the antigenic proteins can be identified and
cloned then expressed in a laboratory to provide material for
vaccination.
• Examples of component vaccines:
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Haemophilus influenzae type b (Hib) vaccine
Hepatitis B (Hep B) vaccine
Hepatitis A (Hep A) vaccine
Pneumoccocal conjugate vaccine
How do diseases evade the
immune response?
• Pathogens that infect the human body have
evolved a number of different techniques for
avoiding the immune response.
• These include:
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Antigenic variation
Antigenic mimicry
Evading macrophage digestion
Hiding in cells
Immune suppression
Disarming antibodies
Avoiding the immune response
•
Antigenic variation
– Some species of protozoan parasites evade immune response by
shedding their antigens upon entering the host.
– Others (e.g. trypanosomes and malarial parasites) can change the surface
antigens that they express so that the specific immune system needs to
make a new antibody to respond to the infection. This is known as
antigenic variation.
•
Antigenic mimicry
– This involves alteration of the pathogen’s surface so that the immune
system does not recognise the pathogen as “non-self”.
– Blood flukes can hijack blood group antigens from host red blood cells and
incorporate them onto their outer surface so that the immune system does
not respond to the infection.
Avoiding the immune response
• Evading macrophage digestion
– Macrophages have an important role in the immune system as they
phagocytosis and destroy foreign material. Some microbes (e.g.
Leishmania) are able to avoid enzymatic breakdown by lysosomes and can
remain and grow inside the macrophage – this means they are able to
avoid the immune system.
– Some bacteria can avoid phagocytosis by releasing an enzyme that
destroys the component of complement that attracts phagocytes.
– Other bacteria can kill phagocytes by releasing a membrane-damaging
toxin
• Hiding in cells
– Bacteria such as heliobacter can invade the epithelial lining of the intestine
to multiply and divide, then transfer into neighbouring cells without entering
the extracellular space where they would be vulnerable to detection.
Avoiding the immune response
• Immune suppression
– Most parasites are able to disrupt the immune system of their host
to some extent.
– HIV is an example of this. It selectively destroys T helper cells,
therefore disabling the host immune system.
• Disarming antibodies
– Bacteria such as Staphylococcus aureus have receptors on their
surface that disrupt the normal function of the host’s antibodies.
– These receptors bind to the constant region (the stem) rather than
the normal antigen binding sites. This prevents normal signalling
between antibodies and other parts of the immune system such as
complement activation or initiating phagocytosis of a bound
antigen.
Reminder:
How do the innate and adaptive
immune system interact to
prevent or overcome infection?
Invader antigens are everywhere!
What does it need to get by?
Skin!
neutrophils
Monoctyes
(macrophages)
Invader
dies!
T - Helper
lymphs
B lymphs
Plasma B
cells
Memory B cells
Antibodies!!
Invader
dies!!
More
T - Helper
lymphs!
Cytotoxic T
lymphs
Invader
dies!!