Antibody diversity. What are the mechanisms used by B cells...

Key Concepts

V(D)J Recombination

This is the process by which B cells assemble immunoglobulin genes from variable (V), diversity (D), and joining (J) gene segments. It forms the foundation of antibody diversity, allowing the generation of numerous unique antibodies through the random selection and recombination of these gene segments during B cell development.

Junctional Diversity

Junctional diversity refers to the introduction of additional variations at the joining sites of V, D, and J segments during recombination. This is achieved through the addition or removal of nucleotides by specialized enzymes, markedly increasing the variability of the antigen-binding site beyond the contributions of V(D)J recombination alone.

Combinatorial Pairing

Combinatorial pairing involves the random association of heavy and light chains to form the complete antigen-binding site of an antibody. Even with a limited set of gene segments, the different possible pairings of these chains create a vast array of unique antibody molecules, contributing significantly to overall diversity.

Somatic Hypermutation

This process occurs after antigen exposure, where B cells introduce point mutations into the variable regions of the immunoglobulin genes. Somatic hypermutation enables the refinement and optimization of antibody affinity through selection, further enhancing antibody diversity and the immune response.

Transcript

0:00 Hey everybody.

00:01 So this question is a bit of a big one.

00:04 It's asking about antibody diversity.

00:07 And it's asking us to identify what the mechanisms are that are used by b cells to generate this really massive diversity.

00:18 Right.

00:19 So we have really a huge number of combinations or potential antibodies that our b cells can produce.

00:27 Right.

00:28 So our b cells, right? so our b cells, are antibody producing cells.

00:33 And they produce antibodies.

00:36 I'm going to just draw one out for us right here.

00:39 And antibodies consist of two heavy chains and two light chains here.

00:49 And they make kind of a y shape.

00:53 We have our two light chains.

00:55 We have our two heavy chains here.

00:59 And that makes up our antibody.

01:01 And here are the tips of each of the heavy and the light chains we have regions here called the hyper -variable regions or the variable regions of our antibody.

01:17 And these are going to be really responsible for most of the diversity that we find within our antibodies.

01:24 However, there are lots of other places that we can find our diversity for our antibodies.

01:30 So the first one that i want to list out is the type of light chain that we can be using or expressing when we have a mature b cell that is that has an antibody fully developed.

01:47 It's mature, so it has completed the cycle of recombining its dna and creating its own antibody.

01:55 And it can use two different kind of gene segments for its light chain.

02:01 So it can either use a kappa chain, so kappa here, kappa light chain, or it can use a lambda light chain.

02:19 So lambda, lambda light chain.

02:32 The use of these two different variations of light chain is one way that b cells introduce diversity here to their antibodies.

02:44 And so another way, and kind of really the main way that our b cells are going to introduce all this diversity in terms of how they can express their antibodies is through vdj recombination and v2j recombination.

03:07 So if we were to zoom into the gene segment that was coding for the heavy chain here of the.

03:16 This antibody.

03:16 So we have two identical heavy chains.

03:19 They're both coated on the same gene.

03:21 So we're going to zoom into the gene segment of this antibody in the maturing b cell, right? so this is before the b cell has created this antibody.

03:30 It's still under development.

03:32 It's still in the bone marrow, right? b cells develop in the bone marrow and then finished development in the spleen.

03:39 I like to remember b goes with bone marrow, so b cells develop in the bone marrow.

03:45 And if we were thinking about how this heavy chain here was created with its variable regions here at the c terminus, we'd think, first of all, about vdj recombination.

03:57 So in this unmature b cell, this immature b cell, there's going to be all these different gene segments within the genome that are going to have the potential to code for different sections of antibody.

04:14 Right...

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