Comment by dm319 | Hacker News Reader

Comment by dm319 | Hacker News Reader

Something article points out, which always blows my mind when I think about it, is that B cells (along with T cells and a recently-discovered neurological cell) are one of only three types of cells which can edit their own DNA. Which is a weird privilege - they are allowed to be different to the rest of us.

Another weird thing about the immune system is that although it is most well-known for it's role in protecting us against pathogens, it actively protects us from cancer on a regular basis. The cancers that do appear in humans are possibly only a tiny percentage of the number that have existed.

The article focusses mainly on B cells. But T cells are a really key anti-viral cell. CD4 T cells coordinate the immune response (B cells included, as well as CD8 T cells, NK cells, innate cells etc etc ). There are a similar number of immune cells in our body as their are neurons, and they theoretically can interact with any other immune cell, communicating in several ways. We are nowhere near understanding how it all works together yet!

As someone recently(ish) diagnosed with an autoimmune condition I spent a good year reading up on the latest papers. We’re still in the fling mud and see what sticks phase of understanding the human body.

> The article focusses mainly on B cells. But T cells are a really key anti-viral cell.

Article about the T cells by the same author: https://berthub.eu/articles/posts/covid-19-t-cells/

I was a little confused on this point. Can an individual B cell change its own DNA, or is it rather that the higher mutation rate means that the set of B cells in the body can be considered as editing its own DNA?

The part of the immune system being described is the germinal center reaction. The 1 million times faster mutation rate only occurs for B-cells dividing in these structures and it's caused by some kind of chemical signaling (the name has slipped my mind). Importantly, it only effects the mutation rate of the thing that codes for the antibody the B-cell expresses, but it has been observed that in this part the mutation is pretty much random.

On average, by the way, there is about 1 point mutation in the part coding for antibodies for every single division in the germinal center. But since the particular mutation is random, I'm not sure I like describing this as the B-cell editing its own genome. It makes it more mysterious than necessary.

I should probably turn this part of my PhD thesis into a set of blog posts once I've defended..."affinity maturation" is a weird and wonderful process.

VDJ recombination is an important part of immune repertoire development

https://en.wikipedia.org/wiki/V(D)J_recombination

B cells also do something called Immunoglobulin class switching to change the structure of antibodies they produce when they encounter their antigen. Different types of antibodies interact with receptors on other cells in the immune system to facilitate the immune response.

https://en.wikipedia.org/wiki/Immunoglobulin_class_switching

https://en.wikipedia.org/wiki/Fc_receptor#Fc-gamma_receptors

Yup they splice and rejoin their DNA in specific sites as part of V(D)J recombination (this isn't the somatic hypermutation the article mainly focuses on, which is a B cell specific process). 'Our' gene editing tools (CRISPR) were not designed by us, but come from nature, so maybe not surprising!

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