Notes
Blood Cell Lines
Sections
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.
Common myeloid progenitor
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.
Common lymphoid progenitor
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.
common myeloid progenitor
Platelets, Erythrocytes, Granulocytes, Macrophages, Osteoclasts
Megakaryoblasts
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.
Megakaryocytes
Under the influence of thrombopoietin, the megakaryoblast matures to form the megakaryocyte.
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.
Erythrocytes
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
In the presence of granulocyte – colony stimulating factor (G-CSF), myeloblasts become neutrophils.
These white blood cells comprise lobulated nuclei and a pale pink cytoplasm.
Agranulocytes:
Monocytes
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.
common lymphoid progenitor
Agranulocytes: T cells, B cells, Plasma Cells
Lymphocytes
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.
Be aware that there is significant intertextual variation regarding the specifics of the hematopoietic pathways. Thus, we will omit details of the contentious relationships between cell lines, and focus only on those chemical signals that are most widely agreed upon.