Awarded to Bruce A. Beutler, Jules A. Hoffmann, and Ralph M. Steinman for their discoveries related to how the immune system is activated to defend against invaders.

Beutler and Hoffmann discovered receptor proteins that can recognize bacteria and other microorganisms and activate innate immunity, the first step in the body's immune response. Steinman discovered the dendritic cells of the immune system and their unique capacity to activate and regulate adaptive immunity, the later stage of the immune response during which microorganisms are cleared from the body, as well as the stage where the immune system develops a "memory" against subsequent infections. Taken together, their insights have shown some of the key activating principles for the stages of immune response, and also mechanisms for disease treatment and prevention.

UPDATE

The Nobel prize announcement was bittersweet for the family and friends of Ralph Steinman. Steinman died just days before the Nobel committee's announcement that he had won. He succumbed to pancreatic cancer, which he had battled for several years, including using the knowledge gained from his Nobel award-winning research. Steinman was honored at a ceremony at Rockefeller University on Monday. Although the Nobel prize is not typically awarded posthumously, the Nobel committee has announced that Dr. Steinman's selection will stand since the committee did not learn of his death until after it had reached its decision.