The Birth of a Monocyte: Inflammatory Language No. 4
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| Monocyte by Asthydays 2012 |
Long before a monocyte is “born,” its ancestor or progenitor, a pluripotent stem cell, lives within bone marrow stromal cells and is capable of turning into any other kind of human cell: heart cell, liver cell, or a cell of the blood, to name a few. Some pluripotent stem cells develop into hematopoetic stem cells (HSC) that further develop into the blood cells of the human body—the lymphoid or myeloid cell lines. The myeloid cell line encompasses the platelets, red blood cells, mast cells, basophils, neutrophils, and eosinophils. It also encompasses monocytes, macrophages, and myeloid dendritic cells, leading to the birth of potential reactionaries.
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| From Wikipedia |
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In 1915, the
movie The Birth of a Nation was
released, triggering inflammatory responses all over the United States.
Additionally, it became a recruitment tool for the KKK. The dangerous and faulty
parallel between that movie and the monocyte is this: the monocyte can lead to
inflammatory reactions, and the monocyte can recruit immune or reactionary
cells. The parallel breaks down when there is no need to react, that it would
be wrong and disease-causing to do
so; so the tolerant monocyte just hangs out. There is no inflammation via its doing.
In the
human, the majority of new monocytes are produced in the bone marrow of the vertebrae
or sternum. In fetuses less than 4-5 months gestation, they are produced in the
spleen and liver. Within a niche, a particular microenvironment of the bone marrow
not yet determined, HSCs develop. This niche could be an osteoblastic (cell
that builds bone) niche, an endothelial cell (lining of blood vessel) niche, a multipotent
primitive mesenchymal cell (like CAR and nestin-expressing) niche in the
stromal cells, or a combination of some or all of these.
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| From Wikipedia |
Although the
exact niche for HSC isn’t known, studies have revealed that CXCL12-CXCR4 (ligand-receptor) signaling is
necessary for maintenance of HSC and their progenies. And, by influence of
certain chemokines like interleukin-1 (IL-1), IL-3, IL-6, granulocyte-macrophage
colony stimulating factor (GM-CSF), and stem cell factor (SCF), the myeloid
cell line develops.
GM-CSF
causes further differentiation (specialization) of the myeloid to a myeloblast,
which is further differentiated into basophils, neutrophils, eosinophils, and
monocytes. SCF, GM-CSF, IL-3 and IL-6, and specifically M-CSF aid in the
development of promonoblasts, monoblasts, promonocytes, then finally—monocytes.
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| Macrophage: First Attempt by The Sensitive Scientist 2011 |
The monocytes
can reside within the marrow, be stored in the spleen, or nonchalantly patrol
the blood for microbes—and await activation into macrophages or dendritic
cells. If unchanged, the monocytes eventually die an apoptotic death. Their lack of DNA repair genes may have something to do with this for
macrophages or dendritic cells are able to repair their DNA, and therefore live
longer. I don’t suppose a monocyte considers this either, but it is their life.
Sources:
Apoptosis of monocyte: Bauer M, Goldstein M, Heylmann D, Kaina B (2012) Human Monocytes Undergo Excessive Apoptosis following Temozolomide Activating the ATM/ATR Pathway While Dendritic Cells and Macrophages Are Resistant. PLoS ONE 7(6): e39956. doi:10.1371/journal.pone.0039956
Bone marrow niches for HSC: Sugiyama T, NagasawaT ; Inf lamm Allergy Drug Targets. 2012 June; 11(3): 201–206. Published online 2012 June. doi: 10.2174/187152812800392689
There will
be three Inflammatory Language posts devoted to monocytes. The first of which, Monocyte
Fashion, addressed the style or types of monocytes. This post is the second devoted to monocytes. The third and forthcoming post will address cell trafficking,
from the monocyte’s perspective. Future posts will eventually address the rest of Inflammatory Language, the song.
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