Myeloblast

Myeloblast

Myeloblast
Identifiers
Code TH H2.00.04.3.04002

Anatomical terminology

The myeloblast is a unipotent stem cell, which will differentiate into one of the effectors of the granulocyte series. The stimulation by G-CSF and other cytokines triggers maturation, differentiation, proliferation and cell survival.[1] It is found in the bone marrow.

Origin

These cells descend from the primitive reticulum cells, which are found in the stroma of the marrow. There is also an intermediate phase between the myeloblast and these primitive reticulum cell, namely the hemocytoblast. At this time several developing blood cell lines are available, like erythropoiesis and thrombopoiesis. The granulopoiesis is regulated by humoral agents, like colony-stimulating factor (CSF) and interleukin 3.

Location in the body

Human Myeloblasts

The myeloblasts reside extravascularly in the marrow. The hematopoiesis takes place in the extravascular cavities between the sinuses of the marrow. The wall of the sinuses is composed of two different types of cells, the endothelial cells and the adventitial reticular cells. The hemopoietic cells are aligned in cords or wedges between these sinuses, the myeloblasts and other granular progenitors are concentrated in the subcortical regions of these hemopoietic cords.

Structure

Myeloblasts are rather small cells with a diameter between 14 and 18μm. The major part is occupied by a large oval nucleus composed of very fine nonaggregated chromatin and possesses 3 or more nucleoli. The cytoplasm has basophilic character and is devoid of granules, which is a major difference with its successor, the promyelocyte. The nucleolus is the site of assembly of ribosomal proteins, which are located in various particles dispersed over the cytoplasm. Mitochondria are present but have a rather small size.

The main features that distinguish a myeloblast from a lymphoblast upon microscopic examination are the presence of more prominent nucleoli, the nuclear chromatin being less condensed, and cytoplasmic granules are present.[2]

Function

A comprehensive diagram of human hematopoiesis

The granulopoiesis consists of 5 stages, of which the myeloblast is the first recognizable cell. Next in the differentiation sequence is the promyelocyte, which can develop into one of the three different precursor cells: neutrophilic, basophilic or eosinophilic myelocytes. This proliferation needs five divisions before the final stage is obtained. These divisions all take place in the first three stages of granulopoiesis.

Pathology

The most common problem with malfunctioning myeloblasts is acute myeloblastic leukemia.[3][4] The main clinical features are caused by failure of the hemopoiesis with anemia, hemorrhage and infection as result. There is a progressive accumulation of leukemic cells, because some blast progenitor cells renew themselves and will have a limited differentiated division. Sometimes acute myeloblastic leukemia can be initiated by earlier hematologic disorder, like myelodysplastic syndrome, pancytopenia, or hypoplasia of the bone marrow.

See also

References

  1. ↑ Metcalf, Donald (2008-01-15). "Hematopoietic cytokines". Blood 111 (2): 485–491. doi:10.1182/blood-2007-03-079681. ISSN 0006-4971. PMC 2200848. PMID 18182579.
  2. ↑ Figure 12-14 in: Mitchell, Richard Sheppard; Kumar, Vinay; Abbas, Abul K.; Fausto, Nelson. Robbins Basic Pathology. Philadelphia: Saunders. ISBN 1-4160-2973-7. 8th edition.
  3. ↑ Murohashi I., Tohda S., Suzuki T., Nagata K., Yamashita Y., Nara N.(1989).Autocrine growth mechanisms of the progenitors of blast cells in acute myeloblastic leukemia. Journal of the American Society of Hematology 74, 35-41
  4. ↑ Villamor N., Zarco M-A., Rozman M., Ribera J-M., Feliu E., Montserrat E.(1998).Acute myeloblastic leukemia with minimal myeloid differentiation: phenotypical and ultrastructural characteristics. Leukemia 12, 1071–1075

Further Reading

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