They are sometimes known as the sentinel cells of the immune system, constantly patrolling the borders of the body that form the physical barriers to the outside world – the skin and the inner linings of the lungs, nose, stomach and gut. The dendritic cells are a key part of the immune system, acting as messengers between the innate and the adaptive immune systems. Their main function is to capture antigens from foreign invaders and present them to the cell surface of the T-cells – a kind of early warning of a breach of security.
Innate immunity occurs during the process of inflammation when microbes breach the external barrier to the body. This is often enough to halt the infection but the second part of the immune response is adaptive immunity, when dendritic cells activate T lymphocytes and trigger a cascade of immune reactions, such as the formation of antibodies and killer cells that clear the infection from the body and form a memory of the invading pathogen.
Dendritic cells were discovered in 1973 by a Canadian immunologist called Ralph Steinman while he was working in the lab of Zanvil Cohen at the Rockefeller University in New York. It was while they were studying the spleen cells of mice to try to understand the role of this organ in immunity that they became aware of “accessory cells” of uncertain identify and function. Further work revealed a novel cell with long, drawn-out filaments or “dendrites”, hence the reason why Steinman named them dendritic cells.
Steinman and Cohen noted in their seminal 1973 paper in the Journal of Experimental Medicine: “The nucleus is large, retractile, contorted in shape, and contains small nucleoli (usually two). The abundant cytoplasm is arranged in processes of varying length and width and contains many large spherical mitochondria. In the living state, the cells undergo characteristic movements, and unlike macrophages, do not appear to engage in active endocytosis. The term, dendritic cell, is proposed for this novel cell type.”
Cohen died in 1993, but Steinman went on to head the laboratory that pioneered the investigation of dendritic cells, leading to important treatments for human disease using dendritic cell- and immune-based vaccines and therapies for such conditions as graft rejection, resistance to tumours, autoimmune diseases and other infections, such as the first dendritic, cell-targeted vaccine against HIV.
Steinman won a third share in the 2011 Nobel Prize in Physiology or Medicine, tragically dying of cancer just three days before the announcement was made. Unaware of his death at the time of the Nobel prize announcement, the Nobel Committee made the unprecedented decision that his award would stand despite the rule that only living scientists can receive the Nobel Prize.