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

by Philipp Dettmer

Even if there is no danger, a few of your Dendritic Cells, for example in your skin, will take samples of the stuff floating around in the natural, healthy environment between your cells—a lot of it is self-antigen presumably—and then move to your lymph nodes to show the Adaptive Immune System what it found. You may ask now: How on earth is this a good idea? Wouldn’t a Dendritic Cell that collects self-antigen cause autoimmune diseases? Well, think again—what is one of the main jobs of the Innate Immune System? To provide context to the Adaptive Immune System. So a Dendritic Cell that moves into a lymph node with the context of “everything is fine—this is what I have to show you” can actually prevent autoimmune diseases. Because what it is really doing is “hunting” for T Cells that are autoreactive. That is, able to bind their MHC molecules to your self-antigen. If the Dendritic Cell finds one of these autoreactive T Cells by pure chance, it connects to it to stop it from further wrongdoing. Remember the “kiss” signal the Dendritic Cell gives to T Cells to activate them? The confirmation signal that tells the T Cell that the danger is real? Well, if there is no danger, the Dendritic Cell withholds this kiss signal. And a T Cell that receives an activating signal on their MHC molecules but no loving kiss on the cheek deactivates itself. It doesn’t die immediately, but it can’t get activated again. It is a lame duck from now on and just floats around for the rest of its life...