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REVIEW ARTICLE
Year : 2017  |  Volume : 8  |  Issue : 4  |  Page : 162-166

An insight into the origin, distribution, and techniques of demonstration of Langerhans cells


1 Department of Dental Surgery, Chanditala Rural Hospital, Hooghly, India
2 Department of Oral Medicine and Radiology, Dr. R. Ahmed Dental College and Hospital, Kolkata, West Bengal, India

Date of Web Publication14-Dec-2017

Correspondence Address:
Sarangi Snehanjan
FD-9, Flat No 3, Salt Lake, Kolkata - 700 106, West Bengal
India
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DOI: 10.4103/srmjrds.srmjrds_33_17

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  Abstract 


Langerhans cells (LCs), first described by Paul Langerhans, a German physician in 1868, are dendritic cells predominantly observed in the suprabasal layers of the epidermis and the oral epithelium. These cells belong to the nonkeratinocytic population and lack desmosomal attachments to surrounding cells; thereby appearing as clear cells in histologic sections. Ultrastructurally, the cells are characterized by unique rodshaped Birbeck granules. These cells are endowed with the essential functions of foreign antigen recognition, trapping, and processing. Herein, we have concisely discussed regarding the origin, distribution, and techniques of demonstration of LCs.

Keywords: Antigen processing, dendritic cells, Langerhans cell


How to cite this article:
Snehanjan S, Ritesh A. An insight into the origin, distribution, and techniques of demonstration of Langerhans cells. SRM J Res Dent Sci 2017;8:162-6

How to cite this URL:
Snehanjan S, Ritesh A. An insight into the origin, distribution, and techniques of demonstration of Langerhans cells. SRM J Res Dent Sci [serial online] 2017 [cited 2018 Dec 17];8:162-6. Available from: http://www.srmjrds.in/text.asp?2017/8/4/162/220804




  Introduction Top


Langerhans cells (LCs) constitute a morphologically well-characterized subpopulation (3%–8%) of mammalian epidermal cells and express immune response associated (Ia) antigens, and function as antigen presenting cells (APCs) and allogeneic stimulatory cells to primed T lymphocytes. LCs are the dendritic cells (DCs) of the epidermis, forming one of the first hematopoietic lines of defense against skin pathogens. In contrast to other DCs, LCs arise from hematopoietic precursors that seed the skin before birth. LCs are hematopoietic cells that belong to the myeloid lineage. These are part of the DC lineage, a heterogeneous group of cells that control the induction of adaptive immune responses.

Origin of Langerhans cells

LCs are myeloid cells resident in the epidermis and stratified epithelia of the corneal, buccal, gingival, and genital mucosae. The advent of monoclonal antibodies revealed expression of major histocompatibility complex (MHC) Class II and macrophage antigens and a potential bone marrow (BM) origin.[1]

LCs now might represent tissue-resident myeloid cell, leading some authors to reclassify them as macrophages, although uniquely, they retain genuine DC function. Critically, the demonstration of a primitive origin does not exclude a secondary origin from BM, and the LC network is renewed by BM-derived cells following severe inflammation.[2],[3]

In a study by Ginhoux et al., it has been demonstrated that adult LCs originate from two distinct embryonic sites-primitive yolk sac and fetal liver.[4] The prenatal origin of LCs describes that the mammalian hematopoiesis has multiple overlapping origins. The first myeloid cells, so-called yolk sac macrophages, are generated from primitive erythro-myeloid progenitors (EMP) in the yolk sac at about 16–18 days of human gestation. EMPs have restricted potential and do not produce definitive long-term multipotent hematopoietic stem cells (HSC). The majority of definitive HSCs arise in the aorta-gonad-mesonephros region after 32nd day of gestation and migrate first to the fetal liver and then to the BM.

It has been known for many years that yolk sac macrophages migrate throughout the embryonic tissues, entering the rudimentary skin and brain. The development of LCs and microglia is critically dependent upon the local production of IL-34 acting through the monocyte colony stimulating factor (M-CSF) receptor.[5],[6] In the brain, microglia arise exclusively from yolk sac macrophages, as demonstrated by Hoeffel et al. using a Runx 1 inducible fate-mapping system.[7]

LCs exhibit specific differentiation and homeostatic features, which distinguish them from other DC populations. For example, whereas DC development and homeostasis are critically controlled by FMS-like tyrosine kinase 3 (Flt3) ligand and its receptor Flt3, the receptor for CSF-1R is required for LCs to develop. In contrast to other DCs, which are constantly replaced by a circulating pool of BM-derived committed precursors (Ginhoux et al.), LCs maintain them in situ throughout the life, independent of any input from the BM. Furthermore, LCs resist high-dose ionized radiation and remain of host origin after lethal irradiation and reconstitution with donor congener BM.[8] Recent studies have also examined the molecular regulation of LC development. The requirement of LCs to integrate into an epithelial layer and then to disengage from this layer demands special properties that may be instructive to compare with mesenchymal to epithelial transitions.[9]

The studies of Basset and Turiaf reported that lesions in histiocytosis X-contained cells which appeared to be identical to LC.[10] Ultrastructural studies using electron microscopy found important differences between LCs and melanocytes, indicating that LCs lacked melanin granules but possessed specific cytoplasmic granules that were later defined as Birbeck granules.[11],[12] Various studies have been done, which indicate that LCs are of mesenchymal origin. LCs have been identified in mesodermal tissues such as the dermis,[13] lymph nodes,[14] and thymus.[15]

Hashimoto was the first to speculate that LCs were a self-perpetuating “intraepithelial phagocytic system.”[16] However, it was only in 1979 that Katz et al. and Frelinger's et al. studies unequivocally established the hematopoietic nature of LCs.[17],[18] Studies have shown that the DCs can gradually differentiate into different subtypes in response to different environmental stimuli [Figure 1].[19] Previous studies of DCs in the mouse and humans [20] suggested the presence of cell population of progenitor cells, which were developmentally distinct, comprising of both the myeloid and the lymphoid series. These cells are able to differentiate into distinct DC subtypes and perform distinct functions.[20] Lymphoid progenitors give rise to precursors that differentiate into thymic DCs, interdigitating DCs, and plasmacytoid DCs. Myeloid progenitors give rise to precursors of monocyte/macrophage series, LCs, interstitial DCs, germinal center DCs, and peripheral blood DCs.
Figure 1: Hematopoietic stem cell giving rise to myeloid and lymphoid precursors and ultimately gives rise to Langerhans cell. DC: Dendritic cells

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Therefore, the origin of LCs has been a subject of constant debate. Paul Langerhans [21] and others [22],[23],[24] considered these cells to be a component of the peripheral neural system owing to their dendritic processes, resembling nerve fibers. Some scientists opined that LCs were in some way related to melanocytes. They were thought to represent worn out melanocytes,[25] daughter cells of dividing melanocytes,[26] or melanocytes in an arrested stage of development.[27] Some researchers have suggested an ectodermal origin.[28]


  Distribution of Langerhans Cells Top


A study has shown that the epithelium of the oral mucosa contains about 37 times as many T-lymphocytes as the epidermis of normal skin.[29] The authors also concluded that CD4+ and CD8+ T-cell subsets are equally present in the epithelium of the oral mucosa, and the TH-lymphocytes (T helper cells) play a more important role.[29]

LCs are seen in histological sections stained with hematoxylin and eosin as “clear cells” in suprabasal layers of mucous membranes.[30] The LCs can be visualized as cells with their bodies generally in the middle portion of stratum spinosum. Delicate dendritic processes can often be observed extending to the level of stratum corneum. Their cytoplasmic processes are found in stratum corneum and usually directed toward epithelial surface. Many studies have shown variation in LCs density in relation to age and location in different body regions.[31] According to morphology, LCs have been classified into two types, i.e., Type 1 LCs, which are pyramidal in shape, located in suprabasal layer, and Type 2 LCs, which are spherical, located in the basal layer. Type 1 contains numerous Birbeck granules, electrolucent cytoplasm, and long-branched dendritic processes whereas Type 2 cells, with fewer Birbeck granules, electron-dense cytoplasm, and shorter dendritic processes.

Among the various distinct oral mucosal tissues, the buccal, gingival, and sublingual mucosa are the most studied with regard to their LC composition. This may be attributed to the accessibility of the tissue, similarity to a well-characterized nonoral tissue (buccal mucosa and skin), relevance to oral diseases (gingiva), and due to therapeutic interests (sublingual).


  Buccal Mucosa Top


At least, four different DC subsets can be identified in the buccal tissue based on their expression of CD11c, CD103, epithelial cell adhesion molecule (Ep-CAM), and langerin (CD207): (1) LCs located in the mucosal epithelium, (2) interstitial (or lamina propria) DCs (iDCs), which are the equivalent of dermal DCs, (3) langerin-expressing iDCs that also express the CD103 molecule, and (4) langerin CD103+ iDCs.[32]


  Sublingual Mucosa Top


The epithelium of the sublingual mucosa is particularly thin and thus provides a useful route of entry for antigens, allergens, and drugs. APC in the sublingual mucosa has been analyzed by immunohistochemistry and flow cytometry.[33],[34] These techniques showed that the frequency of LCs in the sublingual epithelium is much lower than in that of the buccal mucosa.[35]


  Gingival Mucosa Top


The gingiva does not contain submucosa and the lamina propria is bound directly to the membrane that lines the outer surface of the alveolar bone. Low percentages of LCs (CD11c MHC class II langerin and Ep-CAM) are located in the gingival epithelium in comparison to buccal and skin tissues.[35]


  Demonstration of Langerhans Cells Top


Hematoxylin and eosin staining

LCs in sections stained with routine hematoxylin and eosin stains cannot be well appreciated. They appear as “clear cells” having a clear halo around their nuclei. LCs being present in the suprabasal layers are also referred to as “high level clear cells,” melanocytes being the “low level clear cells” as present in basal cell layer of stratified squamous epithelium. All these cells, except Merkel cells, lack desmosomal junctions to adjacent cells. During histologic processing, the cytoplasm shrinks around the nucleus to produce the clear halo [19],[31] [Figure 2].
Figure 2: High power photomicrograph of H and E, section showing a Langerhans cell with perinuclear halo and characteristic “coffee bean-” shaped infolded nuclei

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Special staining

One of the first techniques employed to demonstrate LCs was the metal impregnation staining technique using heavy metals such as gold chloride, cobalt, paraphenylenediamine,[13] osmium iodide or zinc osmium iodide, and uranyl acetate–lead staining.[36]

Enzyme histochemistry

The actual sites of cellular enzymatic activity can be demonstrated by enzyme histochemical techniques such as ATPase, which is an excellent method for the identification of human LCs.[36] Other enzymes used, are adenosine diphosphatase (ADPase), 5 nucleotidases, and aminopeptidases.

Immunohistochemistry

A large number surface and cytoplasmic antigens have been localized on LCs by means of antibodies used in different techniques such as immunofluorescence or immunoperoxidase techniques. One of the most prominent features of LCs is the high level of expression of MHC class II antigens. Leukocyte common antigen (CD45), a marker of cells of hematopoietic origin, is also expressed by LCs and shows stresses their BM origin.[36] Many other antigens such as Fc-IgG, CD11, C3b/C4b, CD25, CD29, CD54, CD1D, and CD83 are found only in subpopulations of LCs or are present in such trace amounts that their detection is only possible using extremely sensitive methods. Among all the markers used, CD1a immunolabeling is considered to be the most reliable method to identify the human LCs. Studies have shown that immature DCs express immunohistochemical markers CD1a, b, c, and d.[37] Recent studies have shown that Langerin seems to be the more specific marker for LCs.

It has been proposed that Langerin induces the formation of Birbeck granules. These LC-specific organelles are distributed within the cytoplasm and are thought to be involved in antigen processing.[37]

Electron microscopy

Electron microscopy studies have shown that LCs exhibit a convoluted “coffee bean shaped” nuclei and no tonofilaments or desmosomes. The Birbeck granules are characteristically present in their cytoplasm, which have a three-dimensional profile of a disc. Their size varies from 100 nm to 1 μm. These granules seem to be most specific marker for LCs. Birbeck granules show a vesicle at one end and sometimes at both ends. In cross sections, the granule with vesicle at one end shows a characteristic appearance, which is termed as “tennis racket” appearance [19],[38] [Figure 3].
Figure 3: Electron microscopic appearance of Birbeck granules

Click here to view



  Discussion Top


LCs have served as the prototype DC population, through which many key features have been elucidated, from the collection of antigens to the migration, maturation and trafficking of cells to the T-cell areas of the lymph node.[39] It is now clear that LCs represent a specific DC population that has a unique origin and specific differentiation and homeostatic requirements. These observations are significant in the sense that the skin and presumably the oral mucosa have an epithelial immunologic function being rendered by the LC and helps in interacting with the entire lymphoid system in concert with the LCs.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Introduction
Distribution of ...
Buccal Mucosa
Sublingual Mucosa
Gingival Mucosa
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