The cellular elements of blood are all derived from the multipotent hemocytoblast (a hematopoietic stem cell). The hemocytoblast is capable of giving rise to another hemocytoblast and to different cellular elements in blood. The process that leads to the formation of various blood cell types from a hemocytoblast is called hematopoiesis. There are two major lineages in the hematopoiesis: the myeloid lineage and the lymphoid lineage.
In the myeloid lineage, the hemocytoblast gives rise to a myeloid precursor, called a common myeloid progenitor cell (CMP). The CMP is also called CFU-GEMM. The name stands for colony forming unit – granulocyte, erythrocyte, monocyte, megakaryocyte. This cell is therefore capable of developing and differentiating into any of the cell types mentioned above. Thus, depending on the cell type in which a CFU-GEMM will differentiate to, the CFU-GEMM may follow any of these differentiation pathways:
- erythropoiesis – involving a CFU-GEMM that gives rise to CFU-E (leading to proerythroblasts)
- granulopoiesis – involving a CFU-GEMM that gives rise to CFU-GM (leading to myeloblasts)
- thrombopoiesis – involving a CFU-GEMM that gives rise to CFU-Meg (leading to megakaryoblasts)
- monocytopoiesis – involving a CFU-GEMM that gives rise to CFU-GM (leading to monoblasts as well)
The CFU-GEMM would follow a particular lineage based on the types of growth factors and cytokines present.
- common myeloid progenitor cell
- myeloid stem cell