Blood immune cells, also known as leukocytes, have long been known to play a critical role in the body’s immune system, helping to identify and fight off invading pathogens such as bacteria and viruses. However, recent studies have revealed an unexpected function of these cells: their ability to proliferate.
The ability of a cell to divide and proliferate is essential for life and allows complex organisms to form from a single cell. It also allows for the replacement of worn-out cells with a limited number of “stem” cells, which then proliferate and specialize. In cancer, however, cell proliferation becomes uncontrollable and chaotic.
Researchers from the GIGA Institute at the University of Liège discovered that in a healthy individual, certain blood immune cells, called monocytes, have the ability to proliferate in order to replace tissue macrophages, which are required for our bodies to function properly. This research was published in the journal Nature Immunology.
The formation of complex multicellular organisms, such as humans, necessitates the generation of billions of cells from a small number of progenitor cells, which first proliferate and then acquire specific morphologies and functions as they assemble into tissues and organs.
This is a major fundamental discovery that changes our understanding of the role of cell proliferation in the formation and maintenance of our immune system. Our findings also suggest that an enumeration of blood monocytes, which is traditionally performed during a blood test, would reflect only a small portion of what is going on at the tissue level, such as during infection or inflammation, because monocytes can proliferate when they enter tissues.
Thomas Marichal
Our current understanding indicates that the majority of the cells that comprise a living organism arise from so-called “stem” cells, which divide through a process known as mitosis to produce a greater number of cells. These cells then cease to proliferate in order to specialize, differentiate, and form muscles, the brain, bones, immune cells, and so on. When proliferation is no longer properly regulated, it can lead to the development of a variety of diseases, the most prominent of which is cancer.
In a study published in Nature Immunology, Professor Thomas Marichal (Professor at ULiège, Welbio investigator at the WEL Research Institute) and his team from the GIGA Institute at ULiège discovered that this ability to proliferate is not merely restricted to stem cells, but is also an as-yet-unknown function of blood immune cells, the monocytes.
Indeed, blood monocytes, which were previously thought to be differentiated cells, are capable of proliferating and generating a pool of monocytes in tissues to give rise to macrophages, which are important immune cells that protect us from microbes and support the proper functioning of our organs.
“This is a major fundamental discovery that changes our understanding of the role of cell proliferation in the formation and maintenance of our immune system,” says Thomas Marichal, the study’s director.
“Our findings also suggest that an enumeration of blood monocytes, which is traditionally performed during a blood test, would reflect only a small portion of what is going on at the tissue level, such as during infection or inflammation, because monocytes can proliferate when they enter tissues. Fortunately, this proliferation is extremely well controlled and does not result in a tumoral process,” he adds. It has only one goal: to allow for the most effective replacement of immune cells that populate our tissues: macrophages.”
