| Histiocyte | |
|---|---|
| Details | |
| System | Immune system |
| Identifiers | |
| Latin | macrophagocytus immobilis |
| MeSH | D006644 |
| TH | H2.00.03.0.01009 |
| FMA | 84642 83585, 84642 |
| Anatomical terms of microanatomy | |
Ahistiocyte is a vertebratecell that is part of themononuclear phagocyte system (also known as the reticuloendothelial system or lymphoreticular system). The mononuclear phagocytic system is part of the organism'simmune system. The histiocyte is atissuemacrophage[1] or adendritic cell[2] (histio, diminutive ofhisto, meaningtissue, andcyte, meaningcell). Part of their job is to clear outneutrophils once they've reached the end of their lifespan.
Histiocytes are derived from thebone marrow by multiplication from astem cell. The derived cells migrate from the bone marrow to theblood asmonocytes. They circulate through the body and enter various organs, where they undergo differentiation into histiocytes, which are part of themononuclear phagocytic system (MPS).
However, the termhistiocyte has been used for multiple purposes in the past, and some cells called "histocytes" do not appear to derive from monocytic-macrophage lines.[3] The term Histiocyte can also simply refer to a cell from monocyte origin outside the blood system, such as in a tissue (as in rheumatoid arthritis as palisading histiocytes surrounding fibrinoid necrosis of rheumatoid nodules).
Some sources considerLangerhans cell derivatives to be histiocytes.[4] TheLangerhans cell histiocytosis embeds this interpretation into its name.
Histiocytes have commonhistological and immunophenotypical characteristics (demonstrated byimmunostains). Theircytoplasm iseosinophilic and contains variable amounts oflysosomes. They bear membrane receptors foropsonins, such asIgG and the fragment C3b of complement. They express LCAs (leucocyte common antigens)CD45,CD14,CD33, andCD4 (also expressed byT helper cells).
These histiocytes are part of the immune system by way of two distinct functions:phagocytosis andantigen presentation. Phagocytosis is the main process ofmacrophages andantigen presentation the main property ofdendritic cells (so called because of their star-like cytoplasmic processes).
Macrophages anddendritic 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 histiocytes are distinguishable by theirmorphology,phenotype, and size.
A subset of cells differentiates intoLangerhans cells; this maturation occurs in thesquamous epithelium,lymph nodes,spleen, andbronchiolar epithelium. Langerhans cells are antigen-presenting cells but have undergone further differentiation. Skin Langerhans cells express CD1a, as do corticalthymocytes (cells of the cortex of thethymus gland). They also express S-100, and their cytoplasm contains tennis-racket like ultra-structural inclusions calledBirbeck granules.
Histiocytoses describeneoplasias wherein the proliferative cell is the histiocyte. The most common histiocyte disorders areLangerhans' cell histiocytosis andhaemophagocytic lymphohistiocytosis.[5]