The thymus also plays a role in the development of all kinds of other immune cells, including part of the B cells
The thymus supports the development of our T cells, hence their name. It says so in all textbooks. But researchers at the Leiden University Medical Center (LUMC) now write in Science Immunology that the thymus also plays a role in the development of all kinds of other immune cells, including part of the B cells. This new insight is important to improve regenerative therapies, such as stem cell transplantation.
Where the T cells develop in the thymus, B cells do so in the bone marrow. Here they are ‘trained’ to become mature immune cells that protect us from all kinds of infections. “We have now discovered that some of the B cells also travel to the thymus to be trained there,” says Frank Staal, professor of Molecular Stem Cell Biology. “And not only that, other specialist immune cells, such as monocytes, NK cells and dendritic cells, also appear to develop in the thymus. This complex organ close to the heart therefore has a much broader function than previously thought.”
Not one but three groups of cells populate the thymus
For this study, the researchers asked themselves a very basic question: how does our immune system develop? “It may surprise you, but in fact much is still unknown about this and much of our current knowledge is based on research in the mouse,” says Staal. Using the most advanced techniques, the researchers were now able to delve deeper into this and map out the entire life cycle of various immune cells.
This also led them to discover that the thymus is populated by three different progenitor cell groups, rather than one large group as is now thought. “We saw that these three cell groups enter the thymus at different times. The last group are cells that can rapidly develop into T cells and we have renamed them TSP3 cells. We had never seen that before,” says Staal.
Faster T cells after transplantation
The speed at which these cells develop into full-fledged immune cells offers opportunities for leukemia patients undergoing a stem cell transplant. Staal: “After a stem cell transplant, the immune system has to be rebuilt from scratch. It can sometimes take a very long time for the T cells to return to normal, making these patients susceptible to infections. If we can already bring the cells we transplant into a TSP3-cell state, the patient would in theory have a well-functioning immune system much faster.”
Man versus mouse
Staal and colleagues will investigate this application further and also want to know whether the B cells that develop in the thymus have a different function than the rest of their peers. In addition, according to Staal, these discoveries underline that the mouse as a model for the development of our immune system is far from optimal. “We have now shown that T-cell development in humans is fundamentally different. We hope to use the current techniques to map out the development of our immune system even better in order to arrive at a more correct model.”
Read the full article in Science Immunology
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