Biomedical scientists at the University of California, Riverside say the cells are similar to M cells found in the intestines and respiratory tract.

It came as a surprise to Professor David Lo and his graduate student Diana Del Castillo when researchers in Israel recently approached them for advice on specialized cells called microlayer cells, or M cells, known mostly for their presence in the intestinal epithelium. . . The Israeli group found similar cells in the thymus, an organ located just above the heart that produces lymphocytes, white blood cells that play an important role in the immune system and protect the body against infection.

Lo, University of California, Riverside Distinguished Professor of Biomedical Sciences, School of Medicine, and Del Castillo, NatureThe newly discovered cells in the thymus were confirmed to be similar to M cells. Acting as gatekeepers, M cells are specialized antigen delivery cells for the immune system in organs such as the intestines and lungs. They play an important role in the development of the body’s immune system.

Researchers at the Weizmann Institute of Science in Israel, led by Jacob Abramson, began studying the thymic epithelium in mice before contacting Lo, whose research interests include understanding how M cells in the gut and respiratory tract work to build our immune system.

“I had been working on these cells for several years, so when the Israeli team contacted me, I was intrigued,” Lo said. “I learned that this group was studying the cellular architecture of stromal cells (cells that form certain types of connective tissue) in the thymus, and using a new, cutting-edge method, they identified a population of cells that are very similar to the M cells we see in the gut and respiratory tract. I had never considered looking for M cells in the thymus in my own research.” .”

Fortunately for the Israeli scientists, Del Castillo, under Lo’s guidance, studied mucosal tissue (tissue lining some ducts and organs) in mice in the laboratory and was able to answer many questions, such as where in the thymus the newly discovered cells were located. where they are and what they do there

The unique nature of thymus M cells

“These particular M cells are restricted to a specific region in the thymus and have unique relationships with different cell types and functions,” del Castillo said. “Among the questions these cells currently raise are how similar they are to M cells in other parts of the body and how different they are from where they are found.”

Lo explained that the thymus has been a tissue that has attracted the attention of immunologists for many years because the development of the immune system is focused on and dependent on it.

“This is a deep mystery that continues to attract interest,” he said. “The thymus provides clues as to how the immune system is born. This complex organ, with many different stromal cell types and interactions, is responsible for producing lymphocytes that protect us from infection.”

According to Lo, the newly discovered M cells are very similar to the M cells found in the intestine and respiratory tract.

“But thymic M cells have different origins, which is an interesting puzzle in itself,” he said. “Once they develop, they are very similar to those we studied in the intestine. As we know, M cells capture viruses and microbes that enter the respiratory tract and transfer them to the immune system, which responds to infectious agents. Do M cells do the same in the thymus in terms of organization and function? That’s what we want to know.”

Examining the function of M cells of the thymus

Del Castillo, who is working on a doctorate in biomedical sciences, used genetically modified mice to answer questions from Israeli researchers.

“We found that the new cells were distributed throughout the medullary region of the thymus,” he said. “This has interesting implications for the role and compartmentalization of the thymus, such as how these cells might function to regulate lymphocyte learning in this organ.”

Lo and Del Castillo were surprised to discover that many of the steps involved in mounting an immune response in different parts of the body are repeated in the thymus.

“It is exciting to see that many of these early cellular interactions and development that we have studied extensively in the peripheral immune system occur in the thymus,” Lo said. “We didn’t expect to see these interactions here. It’s like watching a short video in the thymus of what’s happening on a large scale in the environment.”

The thymus also ensures that lymphocytes do not accidentally attack our own tissues; The medulla of the thymus is where these decisions are made, UCR scientists say.

“The recently discovered M cells are part of this decision-making process,” del Castillo said. “The production of antibodies in the peripheral immune system to fight infectious organisms involves several steps and the interaction of many cells with each other. What is striking is that some of these interactions are repeated early in the development of thymic M cells.”

According to Lo, it is conceivable that thymic M cells are then trained to function in such a way that they are ready to communicate and interact with other cells in the periphery when needed.

“The thymus is complex because it constitutes a fully functional immune system and repertoire, and we know that many components play important roles in its functioning,” he said. “We did not expect M cells to even show up in the thymus. So this is an exciting discovery because it is clearly linked to similar processes that occur in the gut and respiratory tract, where 60-70% of infectious agents enter our body.”