Immune: A Journey Into the Mysterious System That Keeps You Alive

by Philipp Dettmer

Activation usually begins with an initial exposure of immune cells to intruders, like bacteria, or danger signals, like the insides of dead cells. For example, Macrophages get activated when they notice an enemy and release cytokines that call up Neutrophils and cause inflammation. The Neutrophils themselves release more Cytokines, causing more inflammation and reactivating Macrophages, who continue fighting. Complement proteins stream into the site of infection from the blood, attack pathogens, opsonize them, and help the soldier cells to swallow the enemies. Dendritic Cells sample enemies and make their way to the Lymph Nodes to activate Helper T Cells or Killer T Cells, or both. Helper T Cells stimulate the innate immune soldiers to continue fighting and create more inflammation. Killer T Cells start killing infected civilian cells with support from Natural Killer Cells. Meanwhile, activated B Cells have turned into Plasma Cells and release millions of Antibodies that stream onto the battlefield and disable the pathogens, maiming them and making them much easier to clear up. This is the immune response in a nutshell.