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I was reading Cellular and Molecular Immunology By Abul K. Abbas, Andrew H. H. Lichtman, Shiv Pillai and stumbled upon the following excerpt $-$

In every individual there are millions of different clones of B-cells,each producing antibody molecules with the same antigen binding site and different in this site from the antibodies produced by other clones.

What are these clones of B-cells, one producing monoclonal antibodies and the other polyclonal antibodies?

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When you read further you'll get it. Basically, when the antibody expressed on a B-cell recognizes an antigen, then the B-cell divides and expands its population to produce more antibodies (through plasma cells). This process is called clonal expansion.

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  • $\begingroup$ This is correct, but a very short summary of a very complex (and cool) process. To expand a bit: After T-cell dependant B-cell activation through an antigen to the B-cell receptor, the B-cell divides into a few very short-lived plasma cells and centroblasts. The latter undergo somatic hypermutation and rapid cell expansion to result in many different B-cells which produce similar, but different antibodies). With the help of follicular T-cells, only centroblast with the antibody with the highest affinity to the antigene survives and this one undergoes clonal expansion. $\endgroup$ – Narusan Oct 28 at 10:57
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    $\begingroup$ @Narusan you are right. I kept the answer very simple because the OP was a beginner in this topic. Also, the reference is the same book (mentioned in the question). $\endgroup$ – WYSIWYG Oct 28 at 13:09
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Cytokines which are produced by effector T4-helper lymphocytes helps activated B-lymphocytes to proliferate and produce clones.

So, even if limited B-lymphocytes may have an antibody molecule able to bind particular epitope, still many cells are produced with the this specificity. This is clonal expansion (https://i.stack.imgur.com/3OlfJ.jpg)

Link for this answer https://bio.libretexts.org/Bookshelves/Microbiology/Book%3A_Microbiology_(Kaiser)/Unit_6%3A_Adaptive_Immunity/13%3A_Humoral_Immunity/13.1%3A_Antibodies_(Immunoglobulins)/13.1E%3A_Clonal_Selection_and_Clonal_Expansion

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  • $\begingroup$ Welcome to Biology.SE! Your answer sounds reasonable, however, it is likely to receive a more favorable response if you include supporting references (primary literature is best, but a textbook available online would seem sufficient for this question). At a minimum, please edit your answer to include the source for the figure. ——— You may also benefit from taking the tour and then consulting the help pages for additional advice on How to Answer effectively on this site. Thanks! 😊 $\endgroup$ – tyersome Oct 27 at 18:23
  • $\begingroup$ Hi Twinkle. If I may offer some advice; please familiarize yourself with formatting. Secondly, and more importantly, please do not answer questions from 4 years ago that are adequately answered. You have been filling the front page with old material that is well suited for the archive! $\endgroup$ – S Pr Oct 28 at 13:45
  • $\begingroup$ Ok will follow your advice $\endgroup$ – Twinkle Sheen Oct 28 at 14:04
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    $\begingroup$ @SPr — You may be correct in suggesting the contributor improves his formatting, although you give no indication of where he is deficient. However I do not accept that the age of the question is relevant if the contributor has something new. I do not regard a three sentence answer as "adequate", and this answer covers a different aspect from WYSIWYG. I would say the problem with this answer is that it does not explain things clearly enough. Of course this is such a basic question covered in text books that perhaps the question should be whether to answer at all. $\endgroup$ – David Oct 28 at 20:37
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B cells are a type of cells that produce antibodies. Each B cell produces a different type of antibody. For example, consider the following B cells: C1, C2, and C3, which produce antibodies A1, A2, and A3, respectively. We are dealing with 3 B cell clones, given that they produce 3 different types of antibodies.

Let's say that the B cell C1 happens to produce antibodies (A1) that are specific against the lipopolysaccharide (LPS) of a certain bacteria. When this bacteria enters the body, C1 will detect its presence and become activated. Two things happen when a B cell becomes activated: (1) differentiation, and (2) proliferation. Therefore, from the B cell clone C1 many more B cells will be produced through cell division, and all of these cells will produce antibodies A1 with the same affinity towards LPS. This would be a monoclonal antibody response, given that only antibodies from one B cell clone are produced.

If B cell C2 also produces antibodies (A2) with affinity for LPS, then upon bacterial infection C2 would become activated, proliferate, and differentiate. Given that antibodies (A1 and A2) from two different B cell clones (C1 and C2) are produced, this is a polyclonal antibody response.

Hope this helps!

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