Tattoos: Unlikely but Plausible Friends of the Immune System
“Humans have marked their bodies with tattoos for thousands of years. These permanent designs—sometimes plain, sometimes elaborate, always personal—have served as amulets, status symbols, declarations of love, signs of religious beliefs, adornments and even forms of punishment.”
Until a few decades ago, the earliest known tattoos were those found on several Egyptian female mummies dated to 2000 B.C. However, the discovery of the Ötzi, an ancient mummified human body found by a German tourist on the Italian-Austrian border in 1991, provided the first evidence that tattoos have been around for more than 5,000 years. Using imaging techniques, anthropologists have mapped 61 tattoos on the mummified Ötzi. The tattoos were made by piercing the skin with a needle, and then rubbing charcoal into it—“and they still look pretty darn good, all things considered.”
Since then, not much has changed. Permanent tattoos are now made by inserting pigments through pricks into the dermis, the lower part of the skin—usually using a hand-held tool that acts similarly to a sewing machine. One or more needles pierce the dermis repeatedly, as many as 200 times per second, opening a void that sucks in the ink while the needles lift out of the skin.
Because the practice of tattooing damages the skin, it challenges the immune system, making people more susceptible to infection. “Once the ink is deposited, there is an inflammatory response that surrounds the ink particles and creates a matrix that allows the ink to stay and not migrate or disappear on its own. It’s inflammatory cells that surround the ink and allow it to stay put.”
The ink is likely picked up by the skin macrophages, and it dwells in these cells for their entire lifespan.
“But much of tattooing remains mysterious: Scientists still aren’t sure what makes certain tattoos fade fast, why others stick around when they’re supposed to disappear, or how they react to light. One of the strangest and least-studied enigmas, though, is how tattoos survive at all. Our immune system is constantly doing its darndest to destroy them—and understanding why it fails could clue us in to one of our bodies’ most important functions, even when we leave the skin blank.”
A study published last week (April 3, 2023) in the American Journal of Biological Anthropology, shows that tattooing increases innate immune activity. The authors view tattooing as a phenotypic gambit. As they explain it, a gambit is the sacrifice of something to gain an advantage. What about the phenotypic gambit, then? It’s the development of traits or behaviors that occur at high rates as part of a refining process of natural selection. Although this process may at first appear costly, it might eventually lead to advantages. For tattooing, it could be increased immunological health deriving from the stimulation of the immune system.
For the study, investigators assessed innate functional immune responses by determining the bacteria-killing activity of saliva samples collected from study participants before and after they received a new tattoo, taking into consideration the extent of body areas covered by tattoos and how many times the study participants underwent tattooing. They found that the dermal stress of tattooing resulted in increased bacteria-killing activity, thus suggesting that people with more exposure to tattoos have a relatively more immediate and active immune response than those with less exposure to tattooing. The investigators conclude that tattoos may elevate innate immunological vigilance, which in turn may protect against future dermal damage.
Interestingly, “It’s also possible—though not yet borne out by data—that learning to coexist with tattoo ink could help immune cells calibrate their reactions to other substances, perhaps even heading off autoimmune attacks.”
Even if turns out that tattoos themselves do not have major impacts on the immune response, they might inspire technology able to boost it. Back in 2008, a Reuters article subtitled “The tattoo of the future may be good for your health rather than just your image” described a study by German investigators. Their research indicated that, in mice, tattooing was a more effective way to deliver a new generation of experimental DNA vaccines than standard injections into muscle. Moreover, a recent study shows that a novel intradermal tattoo-based injection device enhances the immunogenicity of plasmid DNA vaccines. Tattoo-needle techniques may therefore become an effective approach to administer vaccines.
Tattoos have always been fascinating to me because of how much precision tattoo artist have to maintain when piercing needles into a person’s dermis continuously, as mentioned in the post, “as many as 200 times per second.” It makes me even more intrigued since they are believed to play a role in the immune system and the overall health of an individual.
Tattoo ink is often made up of a toxic component known as TiO2 – Titanium dioxide, and it is commonly found in sunscreen and paint. After reading the blog post, it made me ponder how specialized and reactive immune cells, which are an essential part of an individual’s defense system, are not able to evade a highly toxic component.
It made me dwell in the world of research, and I found a study that explained how the different immune cells react to ink being introduced into the dermis. When an individual gets a tattoo, the body’s immune system considers the ink to be a foreign particle and initiates an innate immune response. Macrophages then try to phagocyte the ink particles and destroy them using an acid. This is a strategy used by macrophages known as neutralization. Unfortunately, macrophages fail to neutralize these ink particles because the ink is immune to acid. Acid has no effect on the ink or its particles. This means that macrophages have to use an alternative pathway. This pathway is known as opsonization, where the ink is marked, and the macrophage will phagocyte the ink particles but not destroy them. Thus, the ink remains stored in the macrophage.
Further, it was found that even though macrophages die, the tattoo ink remains in the dermis because, during the apoptosis of macrophages, the ink is released. As the ink is released, it is then absorbed or phagocyted by another macrophage.
This reveals a hidden function of macrophages that not only can they act as phagocytes, but they can even store foreign particles until apoptosis.
This was a very interesting blog post. After reading the article I was curious to know if other studies have found an immunoglobulin to play a role in the immune response after getting tattooed. A study conducted in 2019 “The evolutionary adaptation of body art: Tattooing as costly honest signaling of enhanced immune response in American Samoa” researched whether people with more tattoo experience would have enhanced immune response. Specifically, cultural adaptations such as tattooing or branding cause more short-term stressors, and how this might prime the immune system for a quicker response. The participants were of American Samoa descent. This was interesting because the Samoan Islands have been known to be an area of frequent infectious diseases and scientists thought that tattooing may serve to provide protection. They concluded that post-tattoo Secretory IgA positively correlated with overall tattoo experience. Participants with higher levels of tattoo experience showed elevated IgA levels. In turn, people with less tattoo experience exhibited little to no stress-related immune response. The more current article “Tattooing as a phenotypic gambit” failed to replicate previous findings for the biomarker sIgA, however, they did find that tattooing, which naturally causes dermal stress, increases bacteria-killing activity. This could mean that individuals with more tattoos have a readily active immune response compared to individuals with little to no tattoos. These articles are talking about new research that affects millions of people who participate in the common practice of getting tattooed. I think doing this kind of research is important because it might introduce discoveries about how our body responds to a common stressor, and how the immune system can adapt and react. This research could even affect how future vaccines are given. This was a very insightful study to read, and I’m interested to read further studies on this topic which is somewhat still a mystery.