|
Body
defences:
7. The action of
memory lymphocyte cells in the immune
system
Doc Brown's Biology exam study revision notes
*
There are various sections to work through,
after 1 they can be read and studied in any order.
INDEX
of biology notes on the body's defence mechanisms against infections from
pathogens
*
(7) The
'timeline' of memory lymphocyte action of our immune system - memory cells
When we suffer from a disease that we recover
from, the body makes memory cells that recognise the same
infection if it enters the body again.
The memory cells produce antibodies to destroy the
pathogen, hopefully to prevent us from feeling or being ill - we may
be completely unaware that this has happened.
If the same type of pathogen gets
into your body again, the lymphocyte cells should recognise the danger
and immediately and make lots of antibodies to counteract it - this is
the basis of your immunity, how you become immune from a disease.
Memory lymphocyte white
blood cells (memory cells) are also produced in the immune
response to a pathogen and the harmless forms you are vaccinated
with.
They stay in the body for
a long time and 'remember' a specific antigen on the surface
membrane of a specific pathogen. This means if you get
re-infected, your body's response is much faster and more
effective - you might not even notice any symptoms!
The antibodies produced are
specific to that type of antigen, they will not lock onto any other type of
antigen, hence they are specific to a particular pathogen.
e.g. the antibody for the
measles virus is different to the antibody of chickenpox virus.
The production of antibodies by
the body in recognition of foreign material is called the immune
response.
One the 'blueprint' antibody is
made, it is rapidly reproduced, carried round the body in the
bloodstream, and lock onto the specific invasive pathogens and
kill them.
The immune response mechanism
of the white blood cells is the same in fighting either
bacterial or viral infections.
If a person becomes infected
with the same pathogen microorganism, the appropriate type of white blood cell will automatically,
and quickly, produce the correct specific antibodies to kill the pathogen because of the
first invasion of a particularly pathogen the person has become naturally immune
to the specific infection.
This is because once the
white blood cells have made an antibody in response to a
particular infection, they can easily recognise the specific
bacterium or virus and produce the same antibody again - see
below - more on memory lymphocytes.
This immunity helps prevent the immune person becoming ill again, or at
least minimises the chance of 2nd attack of the specific pathogen having any
significant effect.
Memory lymphocytes are
naturally produced in the immune system's response to a pathogen.
When a pathogen enters your
body for the first time, the immune response is slow because
there are relatively few of the B-lymphocytes around capable of
making the antibody to combat a particular pathogen.
Eventually, your body will
produce enough of specific antibody to overcome the infection,
but in the mean time, you will display symptoms of the disease.
As well as antibodies, memory
lymphocytes are also produced by your immune response to a
foreign antigen of a pathogen. They stay around in the body for
some time and 'remember' a specific antigen on the surface
membrane of a specific pathogen.
The person is now got some immunity to respond much more quickly to a second infection.
See also section on
vaccination-immunisation
If the same pathogen enters
your body again there are far more white blood cells around to
recognise the pathogen and produce antibodies to combat it.
In other words, the secondary
response is faster and stronger than the first immune response,
and, in many cases, destroys the pathogen before you exhibit any
symptoms.
The graph above illustrates the
possible sequence of events involving memory lymphocytes
The body is first exposed to the antigen.
This could be from an actual
pathogen infection or from vaccination with a dead or inactive form
of the pathogen.
In the body's primary response, the lymphocytes produce the antibodies
to counteract the threat of the pathogen.
This takes a little time, but the
specific antibodies increase steadily in concentration.
Eventually, the body overcomes the infection or stops responding to the
vaccination, and the antibody concentration falls.
The memory lymphocytes retain the information to recognise the shape of
the antigen if re-infection occurs.
If the body becomes infected, the memory lymphocytes immediately
recognise the pathogen antigen and rapidly make lots of the specific
antibodies.
Because of the memory
lymphocytes, the 2nd response of your immune system is faster and
stronger.
The specific antibody reaches a maximum concentration to fight the
antigen.
As the infection is gradually overcome the antibody concentration falls.
See this in the next section
with more on
vaccination-immunisation
Epidemics are large
scale outbreaks of an infectious communicable disease.
Mass
vaccination programmes help reduce the chances of an epidemic,
but, a high percentage of a population needs to be vaccinated to
avoid the infection spreading rapidly - this can create 'herd
immunity'.
If a large proportion of the population
is immune to a pathogen, the spread of the
pathogen is very much reduced - this is known as
herd immunity,
which can arise either from mass vaccination or naturally if a high
percentage of the population develop natural immunity to a pathogen
- in either case, lots of people have the antibodies to combat the
pathogen and therefore far less people can be carriers of the
pathogen.
White blood cells
also help to defend against pathogens with antitoxins
Producing antitoxins, which counteract the toxins
released by the pathogens.
These toxic substances are
non-living toxins or pathogens.
They are waste toxins
produced by the cell chemistry of the invading pathogen e.g.
bacterium.
|
