Illustration of the Canadian immunologist Ralph M Steinman (1943-2011). Steinman is best known as the co-discoverer of dendritic cells, a type of immune cell. Dendritic cells are antigen-presenting cells (APCs), that is, they present pathogens or foreign molecules (antigens) to other cells of the immune system to be eliminated. They are the link between the innate immune system, which is the first to react to an infection, and the adaptive immune system, which keeps a memory of pathogens for future reinfection. Steinman was awarded the 2011 Nobel Prize in Physiology or Medicine along with Jules Hoffmann and Bruce Beutler for his discovery.