This popular science article looks at opposing views of the role of macrophages in the development of tumors. Some groups see macrophages as aiding the cancer, and want to suppress them, while others are engaged in turning macrophages into an effective weapon to destroy cancer cells. This two-faced nature echos a range of unrelated work on macrophage behavior. These cells can be classed by their activities into what are known as polarizations. The M1 polarization is aggressive and inflammatory, willing to attack cells and pathogens, while the M2 polarization aids tissue growth and regeneration. The balance between the two shifts according to circumstances. Both are necessary, but M1 is too prevalent throughout the body in older individuals, hindering tissue maintenance. In cancers, the problem is reversed: too many M2 macrophages are present to help the cancer, while too few M1 macrophages actively attempt to destroy its cells.
In the late 2000s, researchers found that leukemia cells highly expressed a gene encoding CD47, a surface molecule known for its role on normal, healthy cells as a “don’t eat me” signal to phagocytosing macrophages. Researchers demonstrated in cell culture experiments that macrophages only engulfed leukemia cells that did not display CD47
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