Tattoos have a very strange effect on our immunity and body

When you get a tattoo and stick ink-filled needles into your skin, your body's immune systems react accordingly. Scientists are not sure if this is good or bad for you, reports The Atlantic.

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In the thousands of years that tattoos have existed, little has changed. The practice still includes the application of a permanent drawing on the body, performed by the method of local trauma to the skin with the introduction of a coloring pigment into the dermis. But much of the tattoo remains a mystery: scientists are still not sure what makes some tattoos disappear quickly, why others stay when they should, and how they react to light. However, one of the strangest and least understood mysteries is how tattoos even survive. Our immune system is constantly doing its best to destroy them. Understanding why it fails can tell us one of the most important functions of our body, even if we do not have a single tattoo.

When a tattoo is applied to the skin, the body considers it an attack. The skin is the immune system's "first barrier" and is replete with fast-acting defense cells that can spring into action when it's compromised, says Juliet Morrison, a virologist at the University of California, Riverside. The main task of these cells is to detect everything foreign and destroy it so that the healing process begins.

Cells absorb ink

The healing process is usually quite successful: burns heal, scars disappear, scabs fall off, except, for some reason, when ink comes into play. The particles in pigments are bulky and difficult for immune cell enzymes to break down. So when ink is ingested by immune cells, such as skin-dwelling macrophages that spend their lives devouring pathogens, cellular debris and other junk in a small patch of flesh, it can turn into a microscopic version of chewing gum. Pigment particles settle in the insides of macrophages, refusing to split. When ink is seen on the surface of the body, it doesn't just weave between skin cells - it shows up from the stomachs of macrophages that can't digest it.

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Sandrine Henri, an immunologist at the French Center for Immunology Marseille-Lumini, and her colleagues found that macrophages' taste for ink may help explain why tattoos remain so tenacious even after the cells die. At the end of the cell's life, which lasts for several days or weeks, the macrophage begins to disintegrate, releasing the pigment from its core. But this ink is immediately picked up and swallowed by another nearby macrophage, which takes the place of its predecessor, just a few micrometers away - less than the thickness of a human hair.

Over time, the edges of the tattoo can become a little more blurry as the ink moves from cell to cell. Some of the pigment can also get into the lymph nodes. These main immunological centers are usually whiter. But in heavily tattooed people, they can eventually become "ink-colored," says Gary Kobinger, an immunologist at the Galveston National Laboratory at the University of Texas Medical Branch. But in general, the ink stays inside the macrophages and thus stays in place. This endless cycle of swallowing, spitting up and re-swallowing, Henri said, is said to be one of the reasons laser tattoo removal is so difficult, and perhaps one of the reasons "temporary" tattoos don't disappear as advertised.

Scientists are not yet sure whether the ink blockage of macrophages has consequences. “What if you make them take care of these foreign pigment clumps instead of doing immune surveillance?” says Morrison.

Ink-enclosed macrophages may be less able to take in more dangerous substances such as pathogens. One study published last year showed that tattoo pigment can alter the proteins that macrophages make and the signals they send to other cells. All this may mean nothing. But it could be that the cell over- or under-reacts to foreign material, potentially putting the immune system at a disadvantage if the new tattoo becomes inflamed, infected, or allergic.

Impact on the immune system: pros and cons

Infections with tattoos are rare - in 5-6% of cases, and if they do occur, they are most often of bacterial origin. But in very, very rare cases, body art fans can contract dangerous viruses, including hepatitis C. Fortunately, especially with modern advances in sanitation, most people with tattoos are "doing fine," says Daniel Tartar, a dermatologist at California university.

Henry, for example, is not worried: the immune system is multifaceted and constantly replenishes its cells. In the event of a serious attack, the cells occupied by the ink will probably be able to call for reinforcements to stop the threat. And it's entirely possible that macrophages are only temporarily disabled by the ink they ingest and eventually return to a new baseline.

Also, the immune system is more than cells that love to eat ink. A few years ago, a team of researchers led by Jennifer Juno, an immunologist at the University of Melbourne in Australia, mixed tattoo ink with a vaccine to track where the contents of an injection given to mice and macaques ended up. There was no evidence that the pigments made immune cells generally "unhappy," as Juno said, or killed them. It doesn't look like the ink has changed the effectiveness of the vaccine.

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Some minor skin lesions, applied by a professional using sterile, hypoallergenic equipment and materials, may even keep nearby immune cells active. Research now shows that macrophages and other so-called innate immune cells can briefly remember some of their past encounters with other types of foreign material and respond better to future attacks. Of course, that's the whole point of vaccination, but vaccines target adaptive immune cells, which are much more receptive to this process. It's also possible - though not yet supported by data - that learning to coexist with tattoo ink may help immune cells calibrate their responses to other substances, possibly even preventing autoimmune attacks, says Tatiana Segura, a biomaterials expert at Duke University.

“If your body tolerates the tattoo at all, it means the immune system has adapted,” says Maria Daniela Hermida, a Buenos Aires-based dermatologist.

Research

To understand some of the immune effects of tattoos, Christopher Lynn, an anthropologist at the University of Alabama, studied people with large tattoos in different parts of the world. He and his colleagues found that people who get tattoos frequently have higher levels of certain immune molecules, including antibodies, in their blood than people who rarely get tattoos (at least for a short time). Maybe, as Lynn said, frequent tattooing gives the immune system a regular low-intensity workout and keeps some parts of our defense arsenal in better shape.

But more antibodies are not the same as better immunity, and researchers don't yet understand how long that effect lasts, says Saranja Wiles, a dermatologist at the Mayo Clinic. And because Lynn and his colleagues didn't run clinical trials in which they had some people get tattooed and others not, they can't actually prove that antibody activity is a direct result of the tattoo.

It's possible, as Lynn said, that people with higher levels of certain immune molecules are more likely to get more tattoos because they're less likely to have a bad reaction. Tattoos in this case would be more of a litmus test for the body, which in a way coincides with the cultural impulse for body art in many cultures: to flaunt one's tolerance for pain. Either way, Lynn warns that even at its best, a tattoo will have its limits.

“I don’t think it will cure a cold,” he said.

Whether or not tattoos themselves boost immunity, they may inspire technologies that do. Kobinger's team is one of the few experimenting with tattoo needle injection techniques to make them more powerful, more effective and easier to administer. Most of the vaccines on our current list are injected deep under the skin, into muscles that are not well supplied with immune cells. The process takes time and decently large doses to really speed up. The skin, in contrast, is “a great place to administer vaccines,” Kobinger said. “The cells are already in place and there is an immediate response,” he says.

There is already a method of administering the vaccine under the skin, called the "intradermal" route, which has been used for vaccinations against smallpox, tuberculosis, and rabies. But administering intradermal vaccines requires a lot of preparation, and when the needles miss the target, the effectiveness of the vaccine can be drastically reduced.

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Vaccine-filled tattoo devices could, in theory, bypass these traps, Kobinger said. In his experiments with various vaccines, the method of tattooing was usually superior to intradermal. Some, though not all, other studies have produced equally encouraging results. Kobinger said that if technology advances, people may someday need fewer injections of some of the multi-dose injections, saving time, money, effort and discomfort. There is no ink. But maybe these needles still have a chance to leave an indelible mark on us.

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