Histiocyte
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A '''histiocyte''' is a [[Cell (biology)|cell]] that is part of the human [[immune system]]; a [[Tissue (biology)|tissue]] [[macrophage]] cell<ref>{{MeshName|histiocyte}}</ref><ref>{{eMedicineDictionary|Histiocyte}}</ref><ref>[http://wordnet.princeton.edu/perl/webwn?s=histiocyte WordNet Search - 3.0<!-- Bot generated title -->]</ref> ("histo-" = "tissue", and "-cyte" = "cell".) Some sources also consider [[Langerhans cell]] derivatives to be histocytes.<ref>{{cite journal |author=Cline M |title=Histiocytes and histiocytosis |journal=Blood |volume=84 |issue=9 |pages=2840–53 |year=1994 |pmid=7524755}}</ref>
All categories of histiocytes are derived from the [[bone marrow]] by multiplication from a [[stem cell]]. The derived cells migrate from the bone marrow to the [[blood]] as [[monocytes]]. They circulate through the body and stop in various organs where they undergo differentiation into histiocytes which are part of the [[mononuclear phagocytic system]] (MPS).
==Overview==
Histiocytes have common [[histology|histological]] and immunophenotypical characteristics (demonstrated by [[immunostaining|immunostains]]). Their [[cytoplasm]] is eosinophilic and contains variable amounts of [[lysosome]]s. They bear membrane receptors for [[opsonin]]s, such as [[IgG]] and the fragment C3b of complement. They express LCAs (leucocyte common antigens) CD45, CD14, CD33 and CD4 (also expressed by [[T helper cell|T Helper Cells]]). These histiocytes are part of the immune system by way of two distinct functions: [[phagocytosis]] and [[antigen presentation]]. Phagocytosis is the main process of [[macrophage]]s and [[antigen]] presentation the main property of [[dendritic cell]]s (so called because of their star-like cytoplasmic processes). Macrophages and dendritic cells are derived from common bone marrow precursor cells that have undergone different differentiation (as histiocytes) under the influence of various environmental (tissue location) and growth factors such as GM-CSF, [[TNF]] and IL-4. The various categories of histocytes are distinguishable by their [[morphology (biology)|morphology]], [[phenotype]] and size.
Macrophages are highly variable in size and morphology, their cytoplasm contains numerous [[acid phosphatase]] laden lysosomes - in relation to their specialised phagocytic function. They express CD68.
Dendritic cells have an indented (bean shaped) nucleus and cytoplasm with thin processes (dendritic). Their main activity is antigen presentation, they express Factor XIIIa, CD1c and Class II [[Human leukocyte antigen]]s.
A subset of cells differentiates into [[Langerhans cells]]; this maturation occurs in the [[squamous epithelium]], [[lymph nodes]], [[spleen]], and [[bronchiolar epithelium]]. Langerhans cells are antigen presenting cells but have undergone further differentiation. Skin Langerhans cells express CD1a as do cortical [[thymocytes]] (cells of the cortex of the [[thymus]] gland). They also express S-100, and their nucleus contains tennis-racket like ultra-structural inclusions called [[Birbeck granules]].
[[Histiocytosis|Histiocytoses]] describe [[neoplasias]] where the proliferative cell is the histiocyte.
==References==
{{reflist}}
{{Blood}}
[[Category:cell biology]]
[[Category:Mononuclear phagocytes]]
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