When the immune system learns to destroy cells, it also remembers the markers for bad cells. If you have (for example) cancerous liver cells and your immune sys

When the immune system learns to destroy cells, it also remembers the markers for bad cells. If you have (for example) cancerous liver cells and your immune system learns to destroy these, the potential exists for it to learn markers that are also present on normal liver cells. After your cancer is gone, this memory that partially (or entirely) applies to regular cells will lead to your immune system trying to destroy normal, healthy cells.