self versus nonself. By the late 1930s, building on Gorer’s work, he slowly narrowed in on a set of genes that determined tolerance. He termed them H genes, for histocompatibility genes—histo from tissue, and compatibility because of their capacity to render foreign tissue to be accepted as self. It was some version of these H genes, Snell realized, that defines the boundary of the immunological self. If organisms shared the H genes, you could transplant tissue from one organism to another. If they didn’t, the transplant would be rejected.
