Leukocytopoiesis

Leukocytopoiesis refers to the formation of leukocytes from stem cells in the bone marrow. Leukocytopoiesis is a subprocess of hematopoiesis (Antwerpes 2022).

Leukocytopoiesis is divided into:

• Granulocytopoiesis
• Monocytopoiesis
• Lymphopoiesis (Antwerpes 2022)

Granulocytopoiesis and monocytopoiesis are part of myelopoiesis. These cells originate from CFU-GEMM progenitor cells and occur exclusively in the bone marrow, whereas lymphopoiesis originates from CLP progenitor cells and can also occur in lymphoid organs (Antwerpes 2022).

Physiology

Multipotent hematopoietic stem cells, known as MHS, are at the beginning of leukocytopoiesis. All blood cells can differentiate from MHS. Cytokines cause MHS to give rise to two types of stem cells:

• Myeloid stem cell (CMP)
• Lymphoid stem cell (CLP)

These cells are now only oligopotent, no longer multipotent.

The three types of granulocytes initially develop together from myeloid stem cells. Differentiation occurs only through the accumulation of specific granules. Starting from the myelocyte stage, it is then possible to distinguish between neutrophil, eosinophil, and basophil forms (Lippert 2011).

Undifferentiated stem cells, a type of basal lymphocyte, arise in the bone marrow (Lippert 2011). From these lymphoid stem cells—also under the influence of cytokines—T and B lymphocytes ultimately develop in the lymphatic system (Antwerpes 2022 / Siegenthaler 2001). T-precursor cells mature into T lymphocytes in the thymus. B-precursor cells, on the other hand, most likely mature in the bone marrow (Lippert 2011).

All types of blood cells are produced in the red bone marrow; only lymphocytes can also be formed in the lymphoid organs (Lippert 2011).

In adults, leukocytopoiesis occurs in the stem cells of the bone marrow, the sternum, the pelvis, the ribs, and the spine. In children, however, it also occurs in the long bones.

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