Singapore: Researchers at Albert Einstein College of Medicine of Yeshiva University, US, and the Icahn School of Medicine at Mount Sinai, US, have found that white blood cells that play a key role in the immune response, also help to both produce and eliminate the body's red blood cells (RBCs). The findings could lead to novel therapies for diseases or conditions in which the red blood cell production is thrown out of balance.

"Our findings offer intriguing new insights into how the body maintains a healthy balance of red blood cells," said study leader Dr Paul Frenette, professor of medicine and of cell biology and director of the Ruth L and David S Gottesman Institute for Stem Cell and Regenerative Medicine Research at Einstein.

Einstein has filed a joint patent application with Mount Sinai related to this research, which is currently available for licensing and further commercialization. Previous studies, all done in the laboratory, had suggested that macrophages in the bone marrow act as nurse cells for erythroblasts, which are RBC precursors. But just how these 'erythroblastic islands' (macrophages surrounded by erythroblasts) function in living animals was unclear.

"What was surprising is that we couldn't see any significant anemia afterward," said Dr Frenette. The researchers then analyzed the lifespan of the red blood cells and found that they were circulating for a longer time than usual. "After we depleted the macrophages in the bone marrow, we discovered that we had also depleted CD169-positive macrophages present in the spleen and liver. It turns out that the macrophages in these two organs are quite important in removing old red blood cells from the peripheral circulation. Taken together, the findings show that these macrophages have a dual role, both producing and clearing red blood cells," he said.

The researchers also examined the role of macrophages in polycythemia vera, a genetic disease in which the bone marrow produces too many RBCs, typically leading to breathing difficulties, dizziness, excessive blood clotting and other symptoms. Using a mouse model of polycythemia vera, they found that depleting CD169-positive macrophages in bone marrow normalizes the RBC count. "This points to a new way to control polycythemia vera," said Dr Frenette. "Right now, the standard of care is phlebotomy [periodic blood removal], which is cumbersome," he added.