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There are two parts to our immune response to a threat, the innate and the adaptive.
The inate system is a general response to threat. This offers mechanical barriers to threats, see part 1, as in the respiratory system, gut and skin. They offer a physical or chemical barrier or are populated with friendly bacteria. Then there are cells that recognise foreigners and consume them – known as phagocytes. There are also proteins that can also recognise invaders and can ‘mark’ them in a way that other cells in the immune system recognise they are to be destroyed. And signalling takes place between cells enabling this to happen.
The adaptive immune response is the next stage – this is highly specific to the threat in question and can take between four hours and four days on first contact with a new invader. In this specific response, we refer to the threat as an antigen because it triggers the immune system to produce antibodies.
An antigen is recognised, ‘captured’ and presented to T lymphocytes which decide what to do with it depending upon what type of antigen it is, virus, bacterium, other. Part of the pathway is to the making of antibodies, also known as immunoglobulins, which are proteins whose function is to identify and neutralise the antigen. They are produced by B lymphocytes.
Every time our immune system responds to an antigen it adds it to its memory and if it meets the same antigen again it remembers it and responds more quickly than the first time limiting its ability to cause us disease. It’s estimated that through life our immune system has the capability to recognise and respond to many billions of unique specific antigens.
More in part 3
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