Editorial: How pathogens are killed

Published in The Hindu on October 7, 2011

Inside our body can be found the bloodiest of battlefields, where millions of organisms are massacred daily, without cease. It is a battle waged by our body’s robust immune system against a wide variety of bacteria, virus, fungi, and parasites. What makes the defence mechanism powerful is the two-level protection conferred by the immune system. The innate immune system that serves as the first line of defence is not antigen-specific; it readily targets all pathogenic organisms the moment they enter the body. The antigen-specific adaptive immune mechanism acts as the second line of protection to keep us healthy. This year’s Nobel Prize in Physiology or Medicine has been awarded to Bruce A. Beutler, Jules A. Hoffmann, and Ralph M. Steinman for revolutionising our understanding of the immune system by discovering the key principles that activate the defence mechanism. Dr. Beutler and Dr. Hoffmann will share half the prize money for discovering the receptor proteins that recognise micro-organisms and activate the innate immunity. The other half of the prize money was awarded to Dr. Steinman for discovering the dendritic cells and understanding their role in adaptive immunity. In 1996, Dr. Hoffmann found that the Toll gene was responsible for sensing pathogenic micro-organisms and that its activation was required for mounting innate immune response. Two years later, Dr. Beutler discovered that components of micro-organisms bind to Toll-like receptors located on many cells. The binding activates the innate immunity, which results in inflammation and destruction of the pathogens.

To Dr. Steinmann goes the great credit of discovering way back in the 1970s that dendritic cells were responsible for adaptive immunity. As they are antigen-specific, dendritic cells take time to react to an invading organism on first exposure; but immunological memory allows them to react more rapidly to the same antigen on subsequent exposures. This is the attribute researchers exploit while designing preventive vaccines. Adaptive immunity holds great medical promise. The immune system can be directed to attack the tumour. Blocking the excessive production of cytokines when diseases show up can ameliorate autoimmunity. Even preventing autoimmune diseases may become possible when certain cells of the immune system are successfully silenced. Dr. Steinmann will go down in history as not just a highly worthy Nobel Prize winner. He was (as a Rockefeller University statement explains) “diagnosed with pancreatic cancer four years ago…his life was extended using a dendritic-cell based immunotherapy of his own design,” and he died three days before his Nobel was announced.