I don' think you understand a lot of what you write. Microplastics are largely inert and most of them are much much bigger than your immunity cells. If they could somehow 'attack' it, they wouldn't be able to consume it (and if they could nothing would change, just like ink in tattoos remains in cca same place even after immune cells consume it).

What would happen during 'attack' is rather a clot forming, not very good ie in your bloodstream. Kind of pearls forming randomly in your body, but the seed would be a piece of plastic instead of a grain of sand, and it would be just your dead immunity cells around it. The chance of getting rid of it gets much smaller. Now why would you want something like that.