The New Immunology — The End of Immunosuppressive Drug Therapy?

In 1970, almost a decade before molecular biology began to make its mark on immunology, Bretscher and Cohn1 advanced a novel theory to explain how the immune system responds to foreign proteins. Stripped to its core and recast in modern terms, their model holds that the initiation of an immune response requires two signals: signal 1 and signal 2. The effect of these signals is to activate lymphocytes of the helper type, which, when activated, can induce B cells to produce antibodies or prepare cytotoxic T cells for cell killing. The necessary activating signals arise when the helper T cell . . .