What kind of proteins are important when you're looking at the immune system? Is there a protein that can attach to thyroid gland cells and signals to the body

What kind of proteins are important when you're looking at the immune system? Is there a protein that can attach to thyroid gland cells and signals to the body that it isn't a threat? Or is there some sort of memory of the immune system with non-threat cells, that mRNA could overwrite? I'm not a biologist, I'd love to read more about these specific inner workings without dissecting a whole undergraduate biology book.