Tattoos survive ever-changing process
We think of tattoos as fixed adornments. Plunge ink deep enough into the skin and there it will sit, suspended in subterranean connective tissue forever.
But tattoos are actually maintained by an ever-changing process — one in which ink crystals are continuously engulfed, freed and gobbled back up, merely giving the illusion of stasis.
That’s what French scientists observed from studying tatted mice. In their model of tattoo persistence, published March 6 in the Journal of Experimental Medicine, macrophages — immune cells that ingest foreign or unhealthy debris in the body — play a starring role. Targeting these cells, the authors suggested, might improve tattoo removal procedures for people.
As a tattoo is given, macrophages descend to capture invading ink. Probably because the ink granules are too bulky for the microscopic Pac-Mans to break down, they hold onto the pigment, your body art shining through their bellies.
With time, these original macrophages die and release their pigments, which get vacuumed up by new macrophages, starting the cycle over, said Sandrine Henri, a researcher at the Immunology Center of Marseille-Luminy who led the study with her colleague Bernard Malissen.
This research “shows that tattoos are in fact much more dynamic than we previously had believed,” said Johann Gudjonsson, a professor of immunology and dermatology at the University of Michigan who was not involved in the study.
For years, researchers suspected that tattoos worked by permanently staining fibroblasts, the cells that synthesize collagen, under the surface of our skin.
Then, looking at tattoo biopsies under the microscope, scientists saw macrophages laden with ink globules, and the story of tattoos became one of the immune system. Still, it was thought that tattoo-bearing macrophages were stable and long-lived, giving tattoos their permanence. What this study suggests is that, at least in mice, these macrophages are constantly being replaced.
The authors speculate that targeting macrophages might enhance laser removal, which can take as many as 20 treatments. An estimated 1 in 5 adults in the United States has at least one tattoo, and tens of thousands of laser removals are performed each year.