Normal Hematopoiesis and Its Regulation

LECTURES , , , ,

Elena B. Vladimirsky

For correspondence: Elena B. Vladimirsky, DSci, Professor, Honored Scientist of Russia; Itamar Ben Avi str., 22/1, Jerusalem, Israel, 92348; Tel.: +972(0)2 650-96-82; e-mail: regblood3@yandex.ru

For citation: Vladimirsky EB. Normal Hematopoiesis and Its Regulation. Clinical oncohematology. 2015;8(2):109–19 (In Russ).

ABSTRACT

Normal hematopoiesis results in production of a great number of cells. The constancy of the qualitative and quantitative composition of the cell component of the hematopoietic system is maintained by the basic hematopoietic law: equal numbers of cell births and deaths occur within each time unit. This balance is provided by three levels of the hematopoietic system: stem cells, growth factors and stromal microenvironment. Hematopoietic stem cells (HSCs) can differentiate into all types of blood cells and at the same time proliferate to preserve the constant number of their pool since no replenishment from external sources occurs during the post-natal period. When the total HSCs count is reduced below the critical level (e.g., by chemotherapy or radiation), they stop differentiating, however they retain the ability for self-renewing until the standard level is reached again. This is the main cause of cytopenia after chemotherapy and radiation; it also explains high efficacy of stem cells transplanting in such cases. Hematopoietic growth factors — glycoproteins — are produced by several blood and stromal cells. The growth factors are essential for realization of any cell program, but the type of the program depends solely on the cell itself: expression of cytokine receptors, features of formation and conduction of cytokine signals, and genetic determination of the cell. The hematopoietic bone marrow cells are situated on spongy bone trabeculae covered with stromal tissue, which consists of cells and the intermediate substance produced by the cells. The hematopoietic function of the stroma is realized through specific adhesion of HSCs and production of growth factors and molecules of cell interaction. Stromal microenvironment also plays a leading role in selective migration of cells from the bone marrow to the circulation system. Evaluation of bone marrow aspirate smear is a very important diagnostic technique for assessment of hematopoiesis. So-called bone marrow indices, i.e. ratios between several types of hematopoietic cells (the myeloid/erythroid index; the index of neutrophil maturation; the index of red cell maturation) have been developed for this purpose. Assessment of these indices together with the bone marrow cellularity, peripheral blood count, and clinical data is very important for expert evaluation of the hematopoiesis and for drawing a proper diagnostic conclusion.

Keywords: hematopoietic stem cells, regulation of hematopoiesis, hematopoietic growth factors, stromal microenvironment, bone marrow indices.

Received: October 13, 2014

Accepted: January 27, 2015

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