Quick question about antibodies.

[starbaduk]

The problem shows a graph depicting increase in particular antibodies after primary and secondary injections of antigens against time.

Solution states that: Before exposure to antigen, there are no antibodies to a particular antigen?

Is this true? Or does it mean that there are very few antibodies of this "type" before the exposure.

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[Dr Gerrard]

This is definitely a weak area for me, but this is what I think. I am pretty sure this is correct.

Before the body comes into contact with the particular antigen, it has never seen it before, so our immune cells cannot even make that antibody. Our bodies do not have an antibody for every single antigen out there, that is for sure, and this is the explanation for that.

 

[Charles_Carmichael]

There are likely B cells with membrane immunoglobulins (mIg) that are specific for the antigen before exposure to the antigen. After exposure the B cell would get activated and will differentiate into plasma cells and memory B cells. The plasma cells secrete massive amounts of antibodies.

So, without being exposed to an antigen, you won't have activation/differentiation of a B cell. Remember that B cells themselves do not secrete antibodies; it's the plasma cells that do. So without activation, which is required for the differentiation into plasma cells, there won't be any antibody secreted that would recognize the particular antigen. That's why you won't find antibodies against an antigen you haven't been exposed to previously. Hope this helps.