Susumu Tonegawa, Japan's first recipient of the Nobel Prize in physiology or medicine and a longtime professor at the Massachusetts Institute of Technology, has died, the university said Wednesday. He was 86.Tonegawa, who died Saturday, won the prize in 1987 for discovering "the genetic principle for the generation of antibody diversity."The discoveries of Tonegawa, a sole recipient of the award, have "increased our knowledge about structure of our immune defense," the Nobel committee said at the time.It praised his work for "improving immunological therapy of different kinds, such as for instance the enforcement of vaccinations and inhibition of reactions during transplantation."Born in Nagoya on Sept. 5, 1939, Tonegawa studied chemistry at Japan's Kyoto University and earned a doctorate…