Pluripotent hemopoietic stem cells or pluripotent hematopoietic stem cells (PHSCs) are stem cells found in the bone marrow. PHSC are the precursor cells which give rise to all the blood cell types of both the myeloid and lymphoid lineages. This includes monocytes and macrophages, neutrophils, basophils, eosinophils, T-cells, B-cells, NK-cells, microglia, erythrocytes (red blood cells), megakaryocytes (e.g. platelets), and dendritic cells. As stem cells, they are defined by their ability to form multiple cells types and their ability to self-renew.

Source

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PHSC are found in the bone marrow of adults, which includes femurs, hip, ribs, sternum, and other bones. Cells can be obtained directly by removal from the hip using a needle and syringe, or from the blood following pre-treatment with cytokines that induce cells to be released from the bone marrow compartment. Other sources for clinical and scientific use include umbilical cord blood and placenta. For scientific purposes, fetal liver of animals is an occasional source.

Colony-forming units

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There are four kinds of colony-forming units:

• Colony-forming unit lymphocyte (CFU-L)
• Colony-forming unit erythrocyte (CFU-E)
• Colony-forming unit granulo-monocyte (CFU-GM)
• Colony-forming unit megakaryocyte (CFU-Me)

Lymphoid

CFU-L

These cells are precursors for lymphocytes. The process of lymphocyte formation is called lymphocytopoiesis.

The cell differentiates as follows:

• Lymphoblast
• Prolymphocyte
• Large lymphocyte
• Small lymphocyte

Prolymphocyte that released into the blood stream and travel to the spleen or lymph nodes differentiate into B-lymphocytes and those that travel into the thymus differentiate into T-lymphocyte.

Myeloid

CFU-E

These cells are precursors for red blood cells, or erythrocytes. The process of red blood cell formation is called erythropoiesis.

The cell differentiates as follows:

1. Proerythroblast
2. Polychromatophilic erythrocyte
3. Normoblast
4. Reticulocyte
5. Erythrocyte

CFU-GM

These cells are precursors for granulocytes (basophil, eosinophil, neutrophil) or monocytes. The processes of cell formation are called granulocytopoiesis and monocytopoiesis

The granulocyte precursor cell differentiates as follows:

• Myeloblast
• Promyelocyte
• Eosino/neutro/basophilic myelocyte
• Eosino/neutro/basophil

The monocyte precursor cell differentiates as follows:

• Promonocyte
• Early monocyte
• Monocyte

Osteoclasts also arise from haemopoietic cells of the monocyte/neutrophil lineage, specifically CFU-GM.

CFU-Me

These cells are precursors for megakaryocytes, which later form blood platelets or thrombocytes. The process of thrombocyte formation is called thrombocytopoiesis.

The cell differentiates as follows:

• Megakaryoblast
• Promegakaryocyte
• Megakaryocyte

Platelets are then formed from the fragmentation of the megakaryocyte cytoplasm.

Nomenclature

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Between 1948 and 1950, the Committee for Clarification of the Nomenclature of Cells and Diseases of the Blood and Blood-forming Organs issued reports on the nomenclature of blood cells. An overview of the terminology is shown below, from earliest to final stage of development:

• ^*blast
• pro^*cyte
• ^*cyte
• meta^*cyte
• mature cell name

The root for CFU-E is "rubri", for CFU-GM is "granulo" or "myelo" and "mono", for CFU-L is "lympho" and for CFU-Me is "megakaryo". According to this terminology, the stages of red blood cell formation would be: rubriblast, prorubricyte, rubricyte, metarubricyte and finally erythrocyte. The nomenclature used in the article seems to be, at present, the most prevalent.

Physical characteristics

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Hematopoietic stem cells morphologically resemble lymphocytes. They are non-adherant, rounded, rounded nucleus, and low cytoplasm to nucleus ratio. Since PHSC can not be isolated as a pure population, it is not possible to identify them in a microscope. The above description is based on the morphological characteristics of a heterogenous population of which PHSC are a component.

Stem cells | Blood and immune system cells