medical school in Boston (1970–91) where he became the Fabyan Professor of comparative Pathology, concurrently serving the Dana–Farber Cancer Institute (1980). He began studying allergies in 1948, and discovered the Ir (immune response) genes that govern transplant rejection in the 1960s. Including a variety of different editions, Benacerraf is an author of over 300 books and articles. At Columbia, Benacerraf got his start in Immunology with Elvin A. Kabat. He spent two years there working on experimental hypersensitivity mechanisms. He then moved to Paris because of family issues and accepted a position in Bernard Halpern's laboratory at the Hôpital Broussais. Here he also formed a close relationship with Italian scientist Guido Biozzi. For six years he worked on the reticuloendothelial function in relation to immunity. The reticuloendothelial function is the white blood cells inside of a barrier tissue. While there they discovered techniques to study the clearance of particulate matter from the blood by the RES (reticuloendothelial system), and devised equations that govern this process in mammals. After six years, Baruj returned to the United States because he could not make his own independent laboratory in France. In the U.S. he developed his own laboratory in New York City and returned to study on hypersensitivity. In New York, Baruj worked with several other immunologists on different fields of hypersensitivity. After working in his New York lab, Baruj turned his attention towards the training of new scientists. Also in this time frame Baruj made the decision to devote himself to his laboratory practices, instead of the family business. At this time Baruj also made the discovery that would go on to win him the Nobel Prize. He noticed that if antigens (something that causes a reaction with the immune system) were injected into animals with a similar heredity, two groups emerged: responders and non-responders. He then conducted further study and found that the dominant autosomal genes, termed the immune response genes, determined the response to certain antigens. This complex process would lead to the understanding of how these genes would determine immune responses. His discovery still holds true, and more has been discovered over the last century. More than 30 genes have been discovered in a gene complex called the major histocompatibility complex. The histocompatibility complex is a complex part of DNA that controls the immune response. This research has also led to clarify autoimmune diseases such as multiple sclerosis and