UK GCSE level age ~14-16, ~US grades 9-10 Biology revision notes re-edit 16/05/2023 [SEARCH]

 Body defences: 7. The action of memory lymphocyte cells in the immune system

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INDEX of biology notes on the body's defence mechanisms against infections from pathogens

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(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.

graph of antibody response to pathogen antigen infection vaccination memory lymphocytes antibodies gcse biology igcse

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.

diagram showing lymphocyte white blood cells producing antitoxins neutralising toxins gcse biology igcse

You can think of these antitoxins as a sort of antibody that combines with the poisonous waste product molecules produced by e.g. by bacteria to form a harmless product - a sort of chemical 'neutralising' effect (but NOT the acid-alkali neutralisation variety!).

1. The microorganism releases toxic substances into the body e.g. tissues or blood.

2. The lymphocyte white blood cells recognise the specific toxin and produces the specific antitoxin.

3. The antitoxin combines with the toxin to produce a harmless 'neutralised' particle that can be disposed of as body waste.

These antitoxins are very specific to individual toxic chemical that remove the toxicity effect of the toxins produced by pathogen cell action.


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