Discovering the origins of immunological competence

Work done in the late 1950s and in the 1960s revealed the role of the thymu s in virus-induced leukemia in mice. Thymectomizing mice at birth to test w hether the virus first multiplied in thymus tissue and then spread elsewher e ultimately led to the conclusion that the thymus was essential to the nor mal development of the immune system. Subsequent testing to try to understa nd how the thymus contributes to the pool of immunocompetent lymphocytes op ened a new chapter in immunology and required a reappraisal of many immunol ogical phenomena and an understanding of the molecular interactions that ta ke place during cell-to-cell interactions.