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

by Philipp Dettmer

As more and more enemies are killed and their numbers are dwindling, fewer and fewer battle cytokines are released, because fewer immune cells are stimulated by ongoing fights. This means no more new soldiers are called in while the old ones die off or stop fighting. The cytokines that cause inflammation are used up relatively quickly, so without new and engaged soldiers that constantly release new cytokines, the inflammation reactions begin receding naturally, which also slowly has the complement system fizzle out. Fewer signals from the battlefield means that the activation of new T Cells first slows down and then stops, while active T Cells become harder to stimulate the longer they are active, until eventually most of them kill themselves. No part of your immune system is made to work forever without stimulation and so if the chain of activations stops, step-by-step, the immune response winds down. In the end your Macrophages devour and clean up the carcasses of the brave immune cells that fought so hard to eradicate the infection to protect you. And so, just as your immune system is winning, it is already shutting itself off without any sort of central planning. Of course there are exceptions because there is one type of cell that actively switches your defenses off and calms down the immune response: Regulatory T Cells. They make up only about 5% of T Cells and in a sense are “opposite Helper T Cells.” For example they can order Dendritic Cells to become worse at act...