H. von Boehmer, P. Kisielow, "Self-nonself discrimination by T cells," Science, 248:1369-73, 1990.
Harald von Boehmer (Basel Institute for Immunology, Switzerland): "Despite 100 years of debate and speculation, the principles and mechanism of the self-nonself discrimination process by the immune system until recently have been obscure. Experimental analyses were hindered by the tremendous diversity of immunologic cells and receptor molecules. By creating T cell receptor transgenic mice--mice whose immune system produces only one receptor--we were able to answer questions about the discrimination between self and nonself in previously impossible detail.
"We have learned that the immature immune system produces cells that would attack every tissue in the body. At the same time, it would also produce cells that, while not harmful, would be useless to the organism. Within the thymus gland, however, the immune system learns which cells would be harmful, useless, or useful to preserve, and acts accordingly."