About 24 years ago, Diana Bianchi peered into a section of the human thyroid gland under a microscope and saw something that instantly gave her goosebumps. The sample was from a woman whose chromosomes are her XX. But through Bianchi’s lens, she saw the unmistakable brilliance of the Y chromosome –dozens and dozens. “Clearly, part of her thyroid was completely male,” Bianchi told me.
Bianchi speculated that the reason may have been pregnancy. A few years ago, the patient was carrying a male fetus, but at some point the cells left the uterus. They ended up being present in his mother’s thyroid, and almost certainly in many other organs, taking over the identity and function of the surrounding female cells, allowing them to function in sync. Bianchi, now director of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, was surprised: “Her thyroid had been completely remodeled by her son’s cells,” she said.
The woman’s case was not a one-off. Each time an embryo implants and begins to grow, it sends a part of itself into the body that houses it.Deposition begins at least at 4th and 5th week of pregnancy.and they colonize almost every part of our anatomy What scientists investigated—Heart, lungs, breasts, colon, kidneys, liver, brain.From there, the cell may remain for some time, grow, and divide decades, or even, as many scientists suspect, identify with the person who impregnated them for the rest of their lives. These can almost be thought of as evolution’s first organ transplants, said J. Lee Nelson of the Fred Hutchinson Cancer Center in Seattle. Microchimerism is considered the most common way in which genetically identical cells mature and develop simultaneously in her two bodies.
These intergenerational transfers go both ways. When fetal cells cross the placenta and enter the maternal tissues, a small number of maternal cells migrate into the fetal tissues, where they may persist into adulthood. Therefore, genetic exchange can occur several times throughout a person’s life. Some researchers believe that people may be miniature human mosaics. many of their relatives by the chain of pregnancy: perhaps their older siblings, or their maternal grandmother, or an uncle or aunt whose grandmother may have become pregnant before the mother was born. “It’s like having a whole family inside you,” Francisco Ubeda de Torres, an evolutionary biologist at Royal Holloway University in London, told me.
This makes microchimerism, named in honor of the half-lion, half-goat, half-dragon chimera of Greek mythology, more common than pregnancy itself. It is thought to affect anyone who has ever carried an embryo, even for a short period of time, and anyone who has ever been in the womb. other mammalsRats, cows, dogs, and our fellow primates also seem to carry around these cellular heirlooms. However, borrowed cells do not always appear in the same location or in the same number. Microchimeric cells are often thought to be present at concentrations on the order of parts per million, levels that are “approaching or reaching the limits of detection in many biological assays.” says immunologist Xing Wei. a pediatrician at Cincinnati Children’s Hospital told me.
Some scientists argue that cells so sparse and inconsistent could not have any meaningful effect. Even among microchimerism researchers, hypotheses about what these cells do, if any at all, remain “very controversial,” Wei said. But many experts argue that microchimeric cells are more than just passive passengers floating in a sea of other people’s genomes. They are genetically distinct entities in foreign homes, with their own evolutionary motivations that may conflict with the homeowner’s motivations. And they can affect many aspects of health, including our susceptibility to infections and autoimmune diseases, and the success of pregnancy. action. If these cells turn out to be as important as some scientists believe, they could become one of the most underappreciated architects of human life.
Researchers have already discovered hints about what these wandering cells are up to.For example, Wei’s research in mice suggests that microchimerism, which babies inherit during pregnancy, may be helpful. fine-tune your immune system, strengthens the newborn’s body against viral infections. As the rodent ages, the mother’s cells may come to the rescue. bring one’s own pregnancy to termBy helping them understand a fetus, half of which is made up of foreign DNA, as something benign rather than an unfamiliar threat.
Similarly, genetic microchimerism found People are Better William Burlingham, a transplant specialist at the University of Wisconsin-Madison, said it’s more important to accept organs from the mother than from the father. In the early ’90s, Burlingham treated a kidney transplant patient who suddenly stopped taking immunosuppressants, which would have caused his body to reject the new organ. But “he was fine,” Burlingham told me.The patient’s kidney was inherited from his mother, and its cells are still circulating in his blood and skin; when his body encountered the transplanted tissue, the newcomers recognized it as the same.
Even the fetal cells that enter the mother’s body during pregnancy may support the baby’s health.David Haig, an evolutionary biologist at Harvard University, believes that these cells may position itself to Optimal extraction of resources from the mother: To encourage more attention in the brain. In the breast, it stimulates more milk production. Induces more body temperature in the thyroid. He said the cells could potentially tinker with a mother’s fertility, extending the time between births and providing more uninterrupted care for her baby. Ubeda de Torres told me that a representative of the fetus could serve as an informant for future offspring living in the same womb.For subsequent fetuses Few associations detected He said that between themselves and their older siblings, the father was greedy when siphoning nutrients from the mother’s body, rather than leaving excess for future siblings who might be different from them. He said it could become.
The benefits of microchimerism for mothers are: more difficult to identify. One possibility is that the more thoroughly the mother’s body is infiltrated by fetal cells, the better the mother’s tolerance for fetal tissue may be, reducing the chance of miscarriage or high-risk birth. “I really think this is insurance for the baby on the mother,” said Amy Boddy, a biological anthropologist at the University of California, Santa Barbara. “It’s like, ‘Hey, don’t attack me.'” Cells that remain in the mother’s body after birth Future pregnancies may become easier (At least by the same father). The more pregnancies you have with the same partner, the rarer pregnancy complications such as preeclampsia will become. And if a mother sends a mobile messenger to her baby, it may be able to do things like: give mom a break It increases sleepiness in children and reduces restlessness.
Microchimerism is not always mother-friendly. Nelson et al. have found that, long term, Women with more fetal cells are also more likely to develop certain autoimmune diseases. This is probably because the child’s cells are incorrectly reevaluated by certain postpartum bodies as unwanted invaders. Nelson’s former postdoctoral fellow, Nathalie Lambert, now at France’s National Institute for Health and Medical Research, has presented evidence that microchimeric cells in the fetus can also produce antibodies that prompt attacks on maternal cells. Lambert said the discovery was made in experiments on mice. But the situation is also more complex than that. “I don’t think they’re the bad guys,” Nelson said of fetal cells crossing over. She and her colleagues also discovered that fetal cells may protect against autoimmunity, which can cause some conditions such as rheumatoid arthritis. actually reduce during and immediately After pregnancy.
In other situations, fetal cells may also bring both help and harm to the mother, or none at all. Fetal-derived microchimeric cells have been found invading the heart tissue of diseased mice. Experiencing a heart attack during the second trimester,settlement Pancreas of newly diabetic mouse motherand lurking Inside a human tumor and caesarean section scar.But scientists aren’t sure Is it a foreign cell? causing damage, repair itor simply a bystander and discovered by chance at these spots.
Wei said these questions are very difficult to answer because studying microchimeric cells is very difficult. Although they can exist in all of us, they are still rare and often hidden in internal tissues that are difficult to access.researcher I can’t say yet Do cells actively deploy to predetermined sites, are they drawn into specific organs by maternal cells, or do they simply follow the natural flow of blood like river sediment? There is also no consensus on how much microchimerism the body can tolerate. Despite the lack of evidence, even microchimerism researchers are bracing themselves for disappointment. “A large part of my mind is prepared to think that most, if not all, microchimerism is completely benign,” said Melissa Wilson, a computational evolutionary biologist at Arizona State University. Told.
But if microchimeric cells play a role in autoimmunity or reproductive success, their therapeutic potential could be enormous. One option, Burlingham said, could be to inject organ transplant patients with their mother’s cells, acting like little ambassadors to coax their bodies into accepting the new tissue. Microchimerism-inspired treatments could help reduce the burden of high-risk pregnancies, Boddy said. Much of this appears to be driven by inappropriately aggressive maternal immune responses. The surrogate mother’s experience could also be improved, and the surrogate mother experience pregnancy complications high blood pressure, premature birth, gestational diabetes, etc. The cells’ stem-like properties could also help researchers design better treatments for genetic diseases in the womb. A research group at the University of California, San Francisco is pursuing this idea. For blood disease alpha thalassemia.
Before these visions become reality, several questions must be answered.The researchers believe that microchimeric cells from different sources can sometimes compete, or even replace each other, compete for superiority. If the same dynamics play out in future treatments, doctors may need to be careful about which cells they introduce into people and when. Otherwise, you may risk losing the precious cargo you have injected. And, perhaps most fundamentally, scientists still can’t figure out how. many Microchimeric cells are needed to affect a given person’s health, a threshold that will likely determine how practical these theoretical treatments are, says UCSB’s Biology of Humanity study. said academic Christine Chua.
Amid this uncertainty, the experts I spoke to support the likely importance of microchimerism. Cells are so persistent, so ubiquitous, so evolutionarily ancient that they must be having an impact, Boddy told me. The simple fact that they are allowed to remain alive for decades while they grow, develop, and change may tell us a lot about immunity and our self-understanding. I don’t know. “In my mind, my concept of who I am has changed,” Bianchi, who herself gave birth to a son, told me. He’s an adult now, but she’s never without him and he’s never without her.