Researchers have found that a rare sub-population of bone-marrow macrophages -- literally the “big eaters” of the immune system -- has another role to play: Each of these rare macrophages can take a stem cell under its wing and prevent its differentiation.
These macrophages guard the stem cells by secreting substances called prostaglandins, which are absorbed by the stem cells. In a chain of biochemical events, these substances delay differentiation and preserve the youthful state of the stem cells.
In addition, the prostaglandins work on the neighboring mesenchymal cells, activating the secretion of a delaying substance in them and increasing the production of receptors for this substance on the stem cells, themselves. This activity, said Professor Tsvee Lapidot of the Weismann Institute’s immunology Department, may help the non-dividing stem cells survive chemotherapy – a known phenomenon. Macrophages also live through the treatment, and they respond by increasing their prostaglandin output, thus heightening their vigilance in protecting the stem cells.Read further in the Weizman Institute's announcement.