How do B cells recognize new antigens?

Question

I’ve been reading about the adaptive immune system and I’m fairly sure I’m misuderstanding a lot of things here.

– B cells develop in the bone marrow
– Each inactive B cell already has a B cell receptor for one specific antigen
– They circulate through the lymphoid system, waiting to randomly come across their specific antigen?

It doesn’t really make sense to me. How do they recognize new antigens if they are born with a specific receptor? Is it some random guess?

Also, how is there a wide variety of immunoglobulines if there’s only IgA, IgM, IgE, IgG and IgD?

Sorry if these questions are stupid, I’m not a med student, just a curious layperson.

In: Biology

Answer 1

First of all…. it’s a bit more complicated that that.

But put simply, it’s a numbers game. B cells are produced to each have thier own random specific receptors. Millions of them. Together, these represent everything your immune system can _possibly_ respond to (with antibodies). This includes all viruses you could respond to, all bacteria, all venoms, just about anything biological. Like a million monkeys with a million typewriters, one of them will have the Shakespeare for whatever disease you have.

One lonely B cell with a perfect receptor for corona virus could’ve been made 10 years ago in your body and has been waiting all this time for its time to shine.

They wait from something to possibly come along and trigger them. The vast majority will wait your entire life and never come across anything that fits their little receptors. But, if they do bump into something that happens to fit, they clone themselves and start producing antibodies that match their specific receptor.

Each antibody of each B cell will be a completely unique ‘key’ that fits a specific lock (or vice versa). IgA, IgE etc just refers to the type of key, not the locks it can open necessarily. You can have flat keys, long round keys… but (hopefully) each individual key is unique. Until you need to open the locks of 1000000 little bacteria and mass produce millions of them that is.

And that is how the immune system do.