Throughout life, the bone marrow continuously produces a variety of blood cell lineages in a tightly controlled, yet flexible process termed haematopoiesis.1 The 2 main groups of mature blood cells are red blood cells (RBCs) and white blood cells (WBCs), or leukocytes.
WBCs are subdivided into:
Myeloid cells scavenge dead host cells and foreign substances, eliminating them directly or presenting them to lymphocytes to stimulate an immune response. The granulocytes-neutrophils, eosinophils, and basophils, named because of their differentially staining intracellular granules-are the most prevalent myeloid lineage in the normal circulation. The granulocyte series of cells, from the least to the most mature stages, are the cells that are massively expanded in CML.
Figure 1. Stem cells and hematopoietic differentiation.
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All mature blood cells originate from a small number of haematopoietic stem cells in the bone marrow. Haematopoietic stem cells are capable of self-renewal or differentiation, the process that leads down lineage pathways towards various mature cell types.
References:
1.Hoffbrand AV, Pettit JE, Moss PAH. Essential Haematology. 4th ed. Oxford, UK: Blackwell Science; 2001.
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