ImmunoFilter: How do B cells mature?

March 13, 2007 5:01 PM

ImmunoFilter: How do B cells, which secrete antibodies, get selected for self vs. nonself recognition? Or don't they?

T lymphocytes undergo maturation in the thymus: positive selection to make sure they react with MHC-expressing cells, and negative selection to make sure they don't react with cells expressing self antigens.

B lymphocytes secrete antibodies, which can also recognize self or nonself proteins. My questions are 1) do B cells undergo self/nonself training like T cells, 2) if so, where does it happen, and 3) how does the recognition/selection occur if the antibodies are secreted away from the cell?

Thanks for your help. I have graduate training in molecular & cell biology, but not in immunology.

posted by ObeyScient to science & nature (6 comments total)

According to my trust immunology text, exclusion of self-recognizing B-cells occurs in the bone marrow and in the periphery and occurs via a few different pathways:

1. If the B cell expresses receptors that recognize a multivalent ligand, it undergoes either receptor editing or apoptosis.

2. If it recognizes soluble ligands that cross-link the receptors, they become anergic (ie. migrate to the periphery, but are not active).

3. If it recognizes soluble ligands with low affinity, it matures normally.

Self-tolerance can also be induced in mature B-cells, but the text isn't clear on exactly how this happens.
posted by greatgefilte at 5:53 PM on March 13, 2007

Trusty text, that is.
posted by greatgefilte at 5:54 PM on March 13, 2007

Not rusty text? ;)
posted by ObeyScient at 6:42 PM on March 13, 2007

Heh, it still has a few years left to it, methinks. Let me know if you need more info, I'll see what I can find.
posted by greatgefilte at 7:40 PM on March 13, 2007

There's also something called split tolerance. Since B cells require activation by T cells specific to a particular antigen, and since T cells are apparently more sensitive to antigens in general, it's possible that you may get a B cell that's specific to a self antigen, but no corresponding T cell exists to activate said B cell (since the T cell would've been killed off in the thymus or anergized upon coming into contact with the antigen).
posted by greatgefilte at 8:00 PM on March 13, 2007

It's also important to remember that there are a crazy amount of B cells (10^11-10^13 IIRC) and that they are all, more or less, different. Once an antigen enters the body, a complex pathway eventually gets the antigen to the B cell with the specific receptor and that B cell goes on and proliferates, makes lots of antibodies, and saves some guys for memory cells. Therefore, the self-recognizing B cells are few and far between and the ones that are self-recognizing won't be provoked to multiply.
posted by shokod at 4:44 AM on March 14, 2007