While working on mapping each cell in a file human body Scientists have discovered an elusive type of immune cell that first appears in the womb. The existence of such cells in humans has been hotly debated – until now.
These mysterious cells, known as B-1 cells, were first discovered in mice in the 1980s, according to a 2018 review in Journal of Immunology. These cells appear early in mouse development, in the womb, and produce different types Antibodies when activated. Some of these antibodies stick to mouse cells and help remove dead and dying cells from the body. Activated B-1 cells also make antibodies that act as the first line of defense against pathogens, such as viruses and viruses. bacteria.
After discovering B-1 cells in mice, a research group reported in 2011 that they found equivalent cells in humans, but these results have not been accepted as conclusive evidence. Thomas Rothstein, professor and founding chair of the Department of Investigative Medicine and director of the Center for Immunobiology at Western Michigan Medical School Homer Stryker MD, who was lead author of this earlier work.
Now a new study was published Thursday (12 May) in the journal Scienceprovides strong evidence that B-1 cells emerge early in human development, during stages I and II third. “It confirms and extends work we previously published,” Rothstein, who was not involved in the new research, told Live Science.
“I think this is the most conclusive data to date” that supports the idea that humans carry B-1 cells, said Dr. Nicole Baumgarth, a professor at the UC Davis Center for Immunology and Infectious Diseases, who was not involved in the new study. In theory, these cells may play critical roles in early development, and by studying them further, scientists can improve their understanding of what the development of a healthy immune system in humans looks like, Baumgarth told Live Science.
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A rare look at the developing immune system
The new research is published alongside three other studies by the Human Cell Atlas Consortium (HCA), an international research group working to identify the location, function and characteristics of each cell type in the human body. Together, the four studies — all published May 12 in Science — include analyzes of more than 1 million human cells, representing more than 500 different cell types taken from more than 30 different tissues.
“You can think of it as ‘Google Maps’ of the human body, and it’s really a ‘street map view’ of individual cells and where they are in the tissues we target,” said Sarah Tishman, lead author of the study. Head of the Department of Cytogenetics at the Wellcome Sanger Institute in England and co-chair of the Organizing Committee of the Human Cell Atlas.
In helping to build this atlas of the human body, Tishman and her colleagues recently focused their efforts on it impervious cells, and in particular, immune cells that emerge during early human development. Through this work, they discovered evidence of human B-1 cells. “What we’re showing is that it’s actually present in humans,” Tishman said during a May 10 news briefing.
Analyzes characterized cells from nine developing tissues, such as the thymus, a gland that makes immune cells and hormones, and the embryonic yolk sac, a small structure that nourishes the fetus. early pregnancy. All tissue samples analyzed by the team came from Human Developmental Biology Resource, a UK tissue bank that stores human fetal and fetal tissues, with written permission from donors. They also combined publicly available data from previous HCA studies.
Altogether, the data covered an early period of development from four to 17 weeks after fertilization, during the first and second trimesters of pregnancy.
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The researchers took high-resolution snapshots of this tissue at a scale of 0.001 inches (50 microns), which is thinner than a human hair, Tishman said during the press conference. At the single cell level, the team analyzed allRNA transcripts” in each tissue, which reflect the different proteins each cell makes. Using these transcripts, researchers can make inferences about each cell’s identity and function.
Through this detailed analysis, the team discovered cells that match the description of B-1 cells found in mice, in terms of their traits and timing of appearance.
“In the rat system, B-1 cells appear early — appear first,” Rothstein said. A different type of immune cell, appropriately called B-2, then appears after the first B-1 cells and eventually becomes the most abundant form of B cell in the mouse. The new study suggests that something similar is happening in humans, where B-1 cells originate and are more abundant in early development, Rothstein told Live Science.
What purpose might these special cells serve in human evolution? They may help sculpt new tissue as it forms, Tishman said.
“When you think about fetal development, in general, there’s massive tissue remodeling that’s happening all the time,” Baumgarth said. For example, humans initially develop a strap between their toes, but this strap is clipped again before birth. It’s possible that B-1 cells help direct such trimming in tissues during development, she said, but “this is speculation on my part.”
In addition to sculpting tissue, B-1 cells may provide some level of immune protection against pathogens small enough to cross the placental barrier, Baumgarth said. And she said again, this is speculation.
Rothstein said the new study expands our understanding of how B-1 cells initially develop and could lay the foundation for future studies of how the cells function later in life.
Originally published on Live Science.