How does the immune system have existing blueprints targeting viruses it has never seen before?

Lymphocytes have surface receptors that recognize antigens. These receptors have existing templates that are complementary to the 3D structures of antigens from viruses and other pathogens, even before you encounter these pathogens. How is this possible?

In this episode, I answer the question above, plus I talk about the following:

Lymphocyte types including B cells and T cells

The self vs non-self paradigm of the immune system

How can the immune system generate a large pool of lymphocyte receptors without directly encoding them from inherited DNA?