PRIMARY & SECONDARY RESPONSE TO INFECTION
Before we conclude this brief and simple introduction to our immune system, we must look at the issue of primary and secondary response to infection.
This is very important as it is the basis that underpins our work in immunisation.
As I have mentioned in previous sections, when we first come into contact with a particular micro-organism that we have not met before, our acquired (or specific) immune system is slow to react to it .
First of all, the immune system has to 'recognize' the micro-organism as being 'non-self' (or foreign), then it has to work out how to defeat it and just which parts of the acquired immune system need to be brought into action.
This all takes time, so initially, the innate or non-specific members of the immune system army come into play.
Their brief is to try and hold infection at bay for long enough in order to allow the specific/acquired members of the immune system army to work out how they are going to fight it.
The acquired immune system does this by first matching receptors on the Fab ends of its immunoglobulins to the receptors which are found on the surface of the micro-organism.
One immunoglobulin starts to be involved first of all - can you remember which one it is?
Immunoglobulin M is the immunoglobulin which responds initially, and then after a while IgG joins in.
This response to a primary (or initial) infection is a rather weak one, and we may possibly become very ill from the infection - or even die from it.
This first response to a first infection is, as you would expect, known as the Primary Response.
However, if we survive that infection, our immune system has a technique for ensuring that we do not make such a weak response if we are infected by that particular micro-organism in the future.
Once they have a 'blueprint' of that micro-organism, and how to defeat it, then the memory cells (T-memory lymphocytes and B-memory lymphocytes) will always be able to recognize it immediately and send the message to the relevant parts of our immune system, so that defence against that micro-organism can be organised straight away.
The diagram below should make this process of primary and secondary responses to infection clearer.
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We involve this process of primary and secondary responses to infection when we immunise someone against an infectious disease, but when we immunise someone we infect them with either a killed version of the infecting micro-organism or a weakened version of it - rather than a whole virulent version - so that it will not cause such a severe disease as it might have done.