Embryonic Macrophages Play Crucial Role in Regulating Blood Stem Cells in Bone Marrow

Recent research from the Leibniz Institute on Aging—Fritz Lipmann Institute (FLI) in Jena has uncovered a previously unknown function of immune cells during development: embryonic macrophages significantly influence blood stem cell regulation within the bone marrow. These specialized immune cells are essential for controlling the size of the hematopoietic stem cell pool, which is vital for continuous blood cell production and maintaining a healthy immune system throughout life.

The process of blood formation, or hematopoiesis, involves the constant renewal of immune and blood cells, as they have limited lifespans. Hematopoietic stem cells (HSCs) in the bone marrow are responsible for this renewal. However, the microenvironment or niche in which these stem cells reside, primarily supported by stromal cells, is crucial for their proper function. How this niche develops during embryonic stages has remained largely unclear.

The team led by Prof. Claudia Waskow discovered that macrophages produced during embryonic development play a pivotal role in establishing this crucial niche. Specifically, these embryonic macrophages regulate the formation of blood stem cells and ensure their proper migration into the bone marrow, where they settle and persist for life. Their absence results in fewer blood stem cells and progenitors, impairing the body's ability to generate new blood cells.

Further investigations revealed that two distinct macrophage populations exist in the bone marrow: one derived from embryonic sources and another originating from adult hematopoietic stem cells. While they look similar externally, their functions diverge significantly. Embryonic macrophages are essential not for the initial creation of stem cells, but for ensuring the correct number and migration of HSCs during development.

Hematopoietic stem cells develop elsewhere in the embryo and migrate to the bone marrow guided by chemical signals secreted mainly by stromal cells. Embryonic macrophages orchestrate this migration by regulating the production of these signaling molecules. Without their influence, the migration process becomes dysfunctional, potentially affecting long-term blood and immune system health.

These findings shed light on the complex interactions governing hematopoiesis and highlight the active regulatory role of macrophages during development. Understanding these mechanisms could have significant implications for researching age-related diseases, immune system maintenance, and developing therapeutic strategies to promote healthy aging.

This study emphasizes that macrophages are more than simple immune defenders—they are key players in establishing a supportive environment for lifelong blood cell production.

Source: https://medicalxpress.com/news/2025-05-embryonic-macrophages-blood-stem-cell.html