 In the late 1970s, it was recognized that T lymphocytes could not recognize antigen directly and instead required an interaction with another specialized cell known as the Antigen-presenting cell.Nobel Prize winners, Rolf Zinkernagel and Peter C. Doherty showed that this recognition also required the antigen-presenting cell to be from the same genetic background as the T-cell.That observation, called MHC restriction, led to a conundrum; namely, that the ability of a T cell to recognize foreign antigen also required that it recognize "self."