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

by Philipp Dettmer

The genes that are responsible for the MHC molecules are the most diverse genes in the human gene pool, leading to a huge variety of MHC molecules between individuals. Of all the things that are different between humans, why are the MHC molecules so unique to every person? Well, different types of MHC are better or worse at presenting antigens from different enemies, like one type might be especially good at presenting a specific virus antigen while another type could be great at presenting a bacteria antigen. For humans as a species this is enormously beneficial because it makes it really hard for a single pathogen to wipe us out. For example, when the Black Death ravaged Europe in medieval times, there were people whose MHC class II molecules were just naturally really good at presenting the antigens of the bacterium Yersinia pestis, which caused the plague. They had a higher chance of surviving the disease and making sure humans as a species survived. This is so incredibly crucial for our collective survival that evolution may have made it a contributing factor in mate selection. In human words: You find potential partners with MHC molecules that are different from yours more attractive! OK wait, what? How would you even know this? Well, you can literally smell the difference! The shape of your MHC molecules does influence a number of special molecules that are secreted by your body—which we pick up subconsciously, from the body odor of other people—so you communicate w...