Macrophages: Biology and Role in the Pathology of Diseases Ebook PDF
Macrophages: Biology and Role in the Pathology of Diseases Ebook PDF Monocytes are white blood cells, which are slightly larger than lymphocytes, and are characterized by an irregular nucleus and a light blue cytoplasm.
Monocytes develop in bone marrow from progenitor cells. Here the common myeloid precursor gives rise to the granulocyte–monocyte precursor eventually leading to development of monocytes.
From the bone marrow monocytes go into blood and then migrate into various tissues, where they develop into macrophages. This simple concept by-and-large holds true but there are some additional routes of monocyte travel in that, for instance, it has been demonstrated in the mouse that blood monocytes can return to the bone marrow (Varol et al. 2007 ) and that the spleen forms a reservoir, from which monocytes can be mobilized (Swirski et al. 2009 ).
Also, it is still unclear to what extent monocytes under homeostatic conditions replenish the macrophage populations in the various tissues. Here evidence in the mouse suggests that monocytes do not contribute to the microglia of the brain (Ginhoux et al. 2010 ) while they can replenish macrophages in tissues like kidney and lung .
Also, bone marrow transplantation experiments show that lung macrophages will become of donor type,demonstrating that they are derived from immigrating monocytes (Thomas et al. 1976 ; Hashimoto et al. 2013 ). In addition, monocytes can differentiate into dendritic cells (DC) but we do not know as to whether monocytes give rise to bona fi de tissue DCs or whether most tissue DCs rather derive from specifi c DC precursor cells, which are distinct from monocytes. Whatever their fate,
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