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created by [deleted] on 27/12/2021 at 17:20 UTC

2 upvotes, 2 top-level comments (showing 2)

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Comment by apple-skunk at 28/12/2021 at 02:02 UTC

5 upvotes, 0 direct replies

Antibodies are basically just free lymphocyte receptors*. As part of lymphocyte maturation, lymphocytes must pass the test of not self-reacting; for T lymphocytes for example, this process occurs in the medulla of the thymus. Specifically, B cell receptors are what eventually become antibodies. Therefore, in a healthy human, antibodies have already been previously tested for self-reactivity during B lymphocyte maturation. These B lymphocytes can then copy their receptors and release them as antibodies (after some modification beyond the scope of this comment) after differentiating to plasma cells.

• A caveat is needed when discussing B lymphocytes, whose receptors undergo ‘affinity maturation’ which is where the B cell will actually modify its receptor to bind better to a matching antigen once it is no longer naive. There isn’t evidence to my knowledge that this level of receptor modification significantly produces self-reactive antibodies (unless perhaps the epitope is structurally similar to human protein, e.g. rheumatic fever occurring after a group A strep infection due to molecular mimicry)

Comment by Lepmuru at 28/12/2021 at 12:17 UTC

1 upvotes, 0 direct replies

We do, they are just not usually released into the wild.

T-Cells and B-Cells, our white blood cells, produce similar proteins that are supposed to recognize foreign structures. T-Cells have their T-Cell Receptors (TCRs) and B-Cells produce antibodies that derive from B-Cell Receptors (BCRs).

In order for these immune cells to develop, they need to pass crucial checkpoints in order to be released and not be killed off during their development. The two most important ones are called positive and negative selection.

Positive selection makes sure that the TCRs or BCRs are indeed reactive - meaning they are functional and able to bind epitopes on foreign structures.

Negative selections presents the same receptors with self-antigens (structures of your own body). Only those B-Cells and T-Cells that do not exceed a threshold of reactivity against those self-antigens are allowed to complete their development and are released into your body's periphery to start doing their jobs. If an autoreactive cell is released, it may cause autoimmune reactions, which the body needs to prevent as thoroughly as possible.

If you are interested in how these processes are characterized, you can find a review on B-Cell maturation specifically here[1]. It is a bit packed with acronyms and requires knowledge of some immune processes. However, the figures provide a good overview of B-Cell development and maturation.

1: https://www.jci.org/articles/view/78083