The curious friendship between macrophages and tattoos (and how that friendship can become its great weak point).
It has never been easy to explain how tattoos work. While tattoos are ‘forever’, but dermis cells are not: they change many times throughout life. Why don’t they disappear? The key seems to be in the macrophages.
Macrophages are starved cells. A core element of the immune system that specializes in recognizing, engulfing, and destroying damaged, dead, or various types of infections. They are, so to speak, the immune system bullies, the ones who do “the dirty work”. And, to stick with the movie cliché, as good thugs that they are they love tattoos.
Ink, skin and macrophages
For years, tattoos were thought to work by staining fibroblast cells in the dermal layer of the skin. More recently, researchers have suggested that macrophages are attracted to the wound made by the needle and they devour the pigment as if it were an offending pathogen.
However, none of those explanations solved the problem. Now a group of French researchers have discovered that these cells can pass pigment into new cells when they die.
To unravel the problem, two researchers Sandrine Henri and Bernard Malissen from the Marseille-Luminy Immunology Center developed genetically modified mice thanks to which they were able to eliminate macrophages from the dermis and some other tissues. After eliminating them, the cells end up being replaced by new macrophages.
The funny thing is that, although they confirmed that dermal macrophages were the only type of cell that acquired the pigment when they tattooed the tails of mice. However, when these macrophages were removed, the tattoo remained. The only conclusion is that the macrophages release the pigment when they die and weeks later it is absorbed by the new macrophages that take its place.
The weak point of tattoos
This cycle of pigment capture, release and recapture occurs continuously on tattooed skin. “We believe that when tattoo pigment-laden macrophages die during the course of adult life, neighboring macrophages recover the released pigments and dynamically ensure the appearance stable and long-term persistence of tattoos, “explains Henri.
It is true that tattoos can be removed by laser pulses that cause skin cells to die and release their pigment. There, as we now know, it begins a dialectic between macrophages neighbors struggling to maintain pigment and the lymphatic system of the body trying to move it away from the skin.
“Tattoo removal can be improved if we combine laser surgery with the temporary removal of macrophages present in the tattoo area, “the researchers argue.” As a result, the pigment released by laser pulses would not be immediately recaptured, which increases the likelihood that they will drain through lymphatic vessels “.