Cell proliferation from stem cells is vital for organisms to grow and form vital organs. In cancer, however, cell proliferation is no longer controlled and becomes chaotic. Research published in Nature Immunology revealed that monocytes, which are blood immune cells previously thought to be already differentiated, can in fact still proliferate. The study’s researchers at the University of Liège have discovered that, in a healthy individual, monocytes also have this ability to proliferate, in order to replace tissue macrophages.
Monocytes are white blood cells that derive from the bone marrow. A monocyte is part of the innate immune response and functions to regulate cellular homeostasis, especially in the setting of infection and inflammation. They account for approximately 5% of circulating nucleated cells in normal adult blood.
The formation of complex multicellular organisms necessitates billions of cells to be produced from progenitor cells, proliferating and taking on particular morphologies and functions while assembling into tissues and organs. Most of the cells that constitute a living organism are understood to arise from stem cells. When they stop proliferating, they specialise, differentiate and form muscles, brain, bones, immune cells, etc. When proliferation is no longer properly regulated, this can lead to the development of various diseases, chief if which is cancer.
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, previously considered as differentiated cells, are capable of proliferating and generating a pool of monocytes in the tissues in order to give rise to macrophages, which are important immune cells that protect us against microbes and support the proper functioning of our organs.
“This is a major fundamental discovery, which changes our conception of the involvement of cell proliferation in the constitution and maintenance of our immune system,” explains Thomas Marichal, director of the study. “Our finding also suggests that the information that can be drawn from an enumeration of blood monocytes, classically carried out during a blood test, would reflect only little of what is happening at the level of the tissues, during ‘infection or inflammation, for example, since monocytes can proliferate when they enter tissues.”
He also adds, “Fortunately, this proliferation is extremely well controlled and does not lead to a humoral process. It has only one goal: to allow, as effectively as possible, the replacement of immune cells that populate our tissues: the macrophages.”
This discovery was possible thanks to the development of new tools and the use of innovative technologies. “This study is a great example of how technological advances can drive breakthrough scientific discoveries. It would have been extremely difficult, if not impossible, to study with such a resolution this population of proliferating monocytes only 10 years ago. This required the use of state-of-the-art equipment recently acquired at the GIGA Institute, the generation of complex genomic data and very sophisticated bioinformatics analyses,” explains Domien Vanneste, first author of the study.
This study paves the way for future investigations that will evaluate the possibility of manipulating or controlling monocyte proliferation for therapeutic purposes, at the benefit of an enhanced health.
Source: University de Liege
