It is said that we are born alone, live alone and die alone. But it turns out that this is not really so. As we grow inside our mother’s womb, cells from our mother cross over to us via the umbilical cord, and likewise, some of our own cells make that journey in opposite direction. Research has unveiled that these are not just brief courtesy visits, but long term residences, and that these adventurous cells have the ability to take root all over the body. It is not yet clear how these foreign cells manage to outsmart the immune system and continue to grow inside their host for years – perhaps even lifelong – or what exactly they do. But there is evidence that they affect the immune system – sometimes for the worse, and sometimes for the better. Join me in my quest to better understand this intriguing phenomenon called microchimerism, and discover more about who we really are.

(Simplified scheme of maternal and fetal microchimerism. Image: Soon-ok Heijmans)