• 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
Active immunity
Passive immunity
Naturally acquired
Naturally acquired
Artificially acquired Artificially acquired
• 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.
• 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)
• 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.
• There are four main types of vaccinations:
• 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.
• 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
• 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
• 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)
• 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:
•
•
•
•
Haemophilus influenzae type b (Hib) vaccine
Hepatitis B (Hep B) vaccine
Hepatitis A (Hep A) vaccine
Pneumoccocal conjugate vaccine
• Pathogens that infect the human body have evolved a
number of different techniques for avoiding the
immune response.
• These include:
• Antigenic variation
• Antigenic mimicry
• Evading macrophage digestion
• Hiding in cells
• Immune suppression
• Disarming antibodies
• 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.
• 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.
• 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.
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!!