HEMATOPOIETIC STEM CELL:
- Resides in adult red bone marrow. Directed by chemical signals, this stem cell will give rise to all of the blood cells types.
- When PU.1 levels surpass a given threshold, the hematopoietic stem cell gives rise to the common myeloid progenitor (CMP); this progenitor gives rise to 6 of the 7 cell types.
- When levels of PU.1 transcription factor below that threshold, the hematopoietic stem cell gives rise to the common lymphoid progenitor (CPL), which ultimately produces lymphocytes.
CMP:
Megakaryocytes:
- In the presence of interleukin 11, the descendants of the CMP gives rise to megakaryoblasts, which are large basophilic cells with a bean-shaped nucleus;
- Under the influence of thrombopoietin, the megakaryoblast matures to form the megakaryocyte (be aware that thrombopoietin is also referred to as THPO and megakaryocyte growth and development factor (MGDF), and c-Mpl ligand).
- Megakaryoctes are large cells with multilobed, irregular nuclei;
- The plasma membrane of mature cells invaginates to form demarcation membranes that fragment the cytoplasm.
- The fragments are shed into the blood as platelets, aka, thrombocytes, which perform key hemostatic functions.
Erythrocyte:
- Erythropoietin (EPO) initiates the erythroid series, which begins with formation of the proerythroblast and ends with the mature erythrocyte (aka, red blood cell).
Granulocytes:
- Granulocyte-macrophage colony stimulating factor (GM-CSF) triggers formation of the myeloblast, which will give rise to 4 of the 5 white blood cell lines:
Eosinophils
- Interleukin 5 triggers production of eosinophils
- These white blood cells are characterized by multi-lobed nuclei and bright orange/red staining granules.
Basophils
- Interleukin 3 triggers production of basophils, which, as their name implies, are highly basophilic.
(be aware that interleukin 3 has widespread influence over the other cell lines, too.)
Neutrophils
- Presence of granulocyte – colony stimulating factor (G-CSF), myeloblasts become neutrophils.
- These white blood cells comprise lobulated nuclei and a pale pink cytoplasm.
Agranulocytes:
Monocyte
- In the presence of monoblast – colony stimulating factor (M-CSF), the monoblast gives rise to the monocyte
- This white blood cell has a bean-shaped nucleus, with visible chromatin, and blue-gray cytoplasm.
- Outside of the red marrow, the monocyte differentiates:
- In the connective tissues, it becomes a macrophage, which can phagocytose dozens of particles, even damaged red blood cells.
- In the bone, the macrophage becomes an osteoclast, which resorbs bone tissue during growth and remodeling.
CLP
Lymphoblast
- Interleukin 7 facilitates the formation of the lymphoblast, which is a large, spherical cell with a large basophilic nucleus.
- The end product of this developmental line is the lymphocyte.
- T cells mature in the thymus and participate in cell-mediated immunity.
- B cells mature in the bone; upon antigen activation, the B cells become plasma cells and participate in the humoral immune response.
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