Hematopoiesis in the human spleen

Area of Science:

• Hematology
• Stem Cell Biology
• Spleen Function

Background:

• The spleen's role in hematopoiesis diminishes after birth, with bone marrow becoming the primary site.
• Extramedullary hematopoiesis (EMH) can occur in the spleen under certain pathological conditions.

Purpose of the Study:

• To investigate the hematopoietic capacity of the human spleen in patients with and without EMH.
• To determine if the spleen can harbor committed hematopoietic progenitors.

Main Methods:

• Culture of spleen mononuclear cells to assay colony-forming units (CFU-E, BFU-E, CFU-C).
• Histological examination of spleen tissue for evidence of EMH.
• Comparison of hematopoietic progenitor levels in peripheral blood and spleen cells.

Main Results:

• Spleen cells from patients with hereditary spherocytosis, Gaucher disease, Thalassemia major, and ITP showed no colony growth and lacked EMH.
• Peripheral blood in these conditions had normal levels of BFU-E and CFU-C.
• Spleen cells from an osteopetrosis patient demonstrated extensive EMH and high concentrations of BFU-E, CFU-E, and CFU-C.

Conclusions:

• Spleens without EMH do not contain committed hematopoietic progenitors, despite normal peripheral blood precursors.
• In osteopetrosis, the spleen acts as a significant hematopoietic organ, comparable to bone marrow, suggesting a reactivation of its embryonic role.