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When you read about the adaptive immune response, you are often told that the response is specific to each pathogen - that the response is tailored. My question is - to what extent is this really true? And if it is true, how is the response tailored?

I understand that the B cell receptors (and, consequently, the antibodies produced by plasma cells in response to a pathogen) are highly specific. A pathogen will bind specifically to a B cell receptor on a particular B cell and particular antibodies will be produced for that pathogen. Again, T cells are specific for each pathogen.

But, it strikes me that there doesn't seem to be that much variation in what antibodies do. Each antibody is particular to its pathogen, but all antibodies work by doing the same few things, e.g. opsonisation, or inhibiting viruses from infiltrating cells. Yes the antibodies may be specific, but to what extent is it true that the antibody will produce a specific response to a specific pathogen? I mean, does the antibody for staphylococcus affect staphylococcus differently from the way the antibody for listeria affects listeria?

Again, each CD8+ Tc cell is specific to its pathogen, but they then seem to go about killing their target pathogen in very similar ways - inducing apoptosis or lysis via perforin and various cytotoxins. So, again, would the CD8+ Tc cell for influenza respond differently to the CD8+ Tc cell for norovirus?

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You are correct, specificity is in the antibody etc, but the killing/clearing mechanisms are the same in all cases. –  Alan Boyd Jun 13 at 5:05

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The adaptive immune response is highly specific and is made to fit a specific antigen. The antigen binding sites are located on the ends of the two short arms of the Y-shaped molecule, as seen in the figure below:

enter image description here

The recognition site is made of the ends of one short immunoglobulin chain and one long chain. The ends (shown in yellow in the figure) are also called variable regions and are the key to the big variety of different antibodies.

When B cells develop, there B cell receptor (which is basically a membrane bound antibody) is tested if it reacts to components from the own organism. If not, they are released into the periphery (blood stream). These B cells are then called naive, since they haven't come in contact with an antigen. They express a B cell receptor which usually only has a weak affinity to an antigen - but the body produces quite a wide variety of these cells. (see the second figure).

enter image description here

When the body comes in contact with an antigen (like a virus), it is taken up by the so called professional antigen presenting cells (dendritic cells, macrophages, B cells) of the immune system, broken down into small pieces and these are presented to the immune system. This activates the affinity maturation of the B cell receptor, somatic hypermutation and finally the clonal selection of the cells, which produce the antibodies with the highest affinity (the strongest binding) to the antigen.

There are estimates that the human immune system can produce around 10 billion different antibodies. This variability is achieved by the genetic variability of the mutation of the variable region of the antibody (the whole process is nicely explained here).

For further information on this topic I can recommend reading the following articles:

The reaction of the body afterwards is always the same, as you state yourself. The specificity of the adaptive immune response is "only" mediated by the specificity of the antibodies. This also makes the system very strong against new pathogens, since only one part of the system needs to be adapted, while the cascades behind it (like apoptosis) are always the same and can be activated fastly if needed.

This can cause some problems, too. Think about self-antibodies, which occur in autoimmune diseases. Here the body can not distinguish between a legitimate immune response against a foreign antigen and those, which are from the own body.

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Rather than saying that it is specific for an antigen, won't it be better to say that it is specific for an epitope ? –  biogirl Jun 16 at 10:34
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To make it more prescise: It is specific for an epitope of a specific antigen. –  Chris Jun 16 at 10:46

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