Myeloblasts are the least mature form of granulocytes within the granulopoiesis and are derived from multipotent stem cells of the bone marrow. Granulocytes are involved in the defense against infections. If there is a lack of granulocytes, this deficiency may be due to a previous lack of myeloblasts and results in immunodeficiency in the sense of immune deficiency.

What is a myeloblast?

Granulocytes belong to the leukocytes. They are the group of white blood cells that perform important tasks in the immune system and are therefore significantly involved in the defense against infections. Leukocytes are involved, for example, in the recognition of foreign antibodies, in the formation of antigens and in phagocytosis.

Specifically, granulocytes attack pathogens and render them harmless to the organism. The formation of cells takes place in the bone marrow and has multipotent progenitor cells to the base. The processes of formation are summarized by the term granulopoiesis, which is considered to be part of hematopoiesis. From multipotential stem cells of the bone marrow develop the so-called myeloblasts, which are known as the smallest precursor of granulocytes within the Granulopoese. They thus arise from hematopoietic stem cells and represent their first differentiation on the way to the granulocyte. Accordingly, the cells are also referred to as the immature form of granulocytes.

Anatomy & Construction

Myeloblasts are the only granulopoietic cells that show no granulation. The cells are endowed with a round or oval nucleus that has fuzzy boundaries. The cytoplasm of myeloblasts has a delicate bluish appearance due to its basophilia.

All myeloblasts have a size between twelve and 20 microns. The chromatin structure of myeloblasts is considered reticular. Around the cell nucleus of the cells lies a Golgi apparatus, which appears perinuclear as a brightening zone. Unlike so-called proerythroblasts myeloblasts have no plasma evaginations. The myeloblasts belong to the so-called "white series". They account for less than five percent of nucleated cells. Their progenitor cells are called hemocytoblast.

In the stage after myeloblast, the resulting granulocyte precursors are called promyelocytes. On the way of the myeloblast to the full-fledged granulocyte are other cell stages. On the metamyelocytes follows the granular column and finally the granular granulocyte.

Function & Tasks

The role of myeloblasts lies in the differentiation to granulocytes. So myeloblasts do not have any active tasks in the human immune system and are not yet involved in the detection and defense of foreign body pathogens. They merely form a stage of development of the granulocytes, which is responsible for the detection and defense of pathogens. With their involvement in granulopoiesis, they are also involved in hematopoiesis on a larger scale.

As such, blood formation in the bone marrow is referred to. Without the formation of granulocytes from myeloblasts, the infection defense of patients is disturbed. For example, if there are too few myeloblasts that make up granulocytes, there are too few immune system immune cells in the patient's blood. Thus, the patient is immune-deficient and more susceptible to infections of all kinds. The exaggerated development of granulocytes from myeloblasts is an indication of an excessively strong immune system and may be a disease sign.

The term neutropenia refers to the lack of granulocytes. Granulocytosis has an increased granulocyte count. The myeloblasts are involved in the precursor stage of the granulocytes in both the one and the other. Although myeloblasts do not have an active immunological function, they nevertheless have a major impact on the functioning of the immune system.


In a so-called neutrophilic granulocytosis neutrophilic granulocytes exceed the threshold 6.3 G / l. This form of excessive formation of granulocytes from myeloblasts may be indicative of leukemia or other malignant tumors, but may also accompany infectious diseases, inflammation or stress.

Eosinophilic granulocytosis refers to a pathological proliferation of eosinophilic granulocytes in peripheral blood. In most cases, abnormal granulopoiesis is due to an allergic reaction. In some cases, the phenomenon is also observed in parasitic infestations. In basophilic granulocytosis basophilic granulocytes multiply above the limit. This form of granulocytosis usually occurs together with eosinophilic granulocytosis and is favored by allergies or hypersensitivity reactions. Parasitosis and hyperlipidemia are also conceivable causes.

In a pathological reduction of neutrophilic granulocytes neutrophilic and other granulocytes are missing proportionately within the blood. This neutropenia is the most common leukopenia. For the patient, the phenomenon is critical, since its ability to fight off infections by reducing the granulocytes is significantly reduced. Especially for bacterial infections, those affected are much more susceptible. Neutropenia can occur if too few granulocytes are formed from myeloblasts. This is the case in the context of inadequate bone marrow proliferation.

In this phenomenon, due to a lack of certain substances, a diminished differentiation of granulocytes from myeloblasts is triggered, for example by a lack of folic acid. In addition, displacement of hematopoiesis can lead to decreased granulocyte formation from myeloblasts. Such displacement occurs, for example, in neoplasias, but may also be a side effect of cytotoxic drugs that interfere with hematopoiesis. Theoretically, the processes and cell stages of granulopoiesis can also be genetically impaired, for example in the context of certain mutations.

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