our adaptive immune system has the largest library in the universe. We learned that after they are born, your T Cells rearrange a few select gene fragments to create billions of different receptors (each T Cell carries only one receptor type). And that in total these many different T Cells, each with its own unique receptor, are able to recognize every possible antigen in the universe. To make sure your own adaptive immune cells do not accidentally recognize and attack your own body, these T Cells have to undergo a rigorous training that only a tiny minority survives. But in the end you get a
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