Are plasma cells part of the immune system?

Are plasma cells part of the immune system? So the plasma cells are a really interesting part of the immune system because they spend their majority of their life being dormant. Theoretically, if you get the measles vaccine when you're a child, you have a plasma cell or a population of plasma cells sitting in your body somewhere that is ready to start making an antibody to the measles virus if you're ever exposed to it down the road. Sometimes that works, sometimes you lose your immunity and that's why you need boosters and things like that. But the cells in general don't do much unless you have that stimulus, unless you are exposed to that virus. So plasma cells are able to live in a sort of a dormant state for a long period of time, which is why honestly we can't eradicate them. That's why cells that are very able to sort of lie dormant, like a spore almost, it's almost nearly impossible to eradicate them. And that's why we really can't cure myeloma because they just are so dormant that there's very little you can do to really eradicate every single one of them.