Researchers from the Children’s Medical Center Research Institute at UT Southwestern (CRI) have discovered a secondary source of blood cells. Upon episodes of extensive tissue damage or bleeding, an emergency response activates the spleen to form blood cells. The findings were published in the journal Nature.
Hematopoietic cells, the ones that make new blood cells, are located in the bone marrow, where these cells are formed in common circumstances. But in stressful events that can lead to excessive blood loss, hematopoietic cells migrate from the bone marrow to the spleen, which becomes a hematopoietic organ too. The activation is very quick thanks to the existence of supportive cells in the spleen that are ready to suddenly receive a big population of blood forming stem cells.
To determine the specific environment (niche) inside the spleen where blood cell formation happens, the researchers examined the expression patterns of two known niche cell factors, stem cell factor (SCF) and CXCL12, in mice. The expression was found to be abundant near sinusoidal blood vessels, a space populated by endothelial and perivascular stromal cells, in a microenvironment very similar to the bone marrow. Under emergency episodes, the endothelial and perivascular stromal cells receive stimuli that make them proliferate to sustain the incoming population of hematopoietic cells.
The physiological relevance of the spleen in blood formation
Without the mechanism that activates the spleen as a secondary source of hematopoietic cells, the mice could not maintain a sufficient number of blood cells during tissue damage or pregnancy.
This new found role of the spleen could lead to developing new therapeutic measures to increase blood cell formation after chemotherapy or bone marrow transplantation, allowing a faster recovery of blood cell counts.
Source: UT Southwestern Medical Center