Intraepithelial lymphocytes and Langerhans cells in the oral mucosa--dynamic aspects.

In the oral epithelium a constant population of non-epithelial immunocompetent cells--lymphocytes and Langerhans cells exists. 3025 such cells of the murine and 542 of the normal human oral mucosa were documented photographically at the ultrastructural level. Location within the epithelium, morphological signs of locomotion, membrane configuration and labeling of the intercellular substance by ruthenium red were registered. About 40 per cent of the lymphocytes and 70 per cent of the Langerhans cells show signs of locomotion, predominantly in a lateral and basal direction. Occasional cells crossing the basal lamina are seen. Close apposition, or rarely a denticulated surface and lysis of desmosomes were present, both probably indications of cellular interactions. Ruthenium red labeling of the glycocalix is continuous forming a homogeneous layer between epithelial and non-epithelial cells and between intraepithelial cells, suggesting an even distribution of antigens and the lack of preformed spaces for intraepithelial cells. Murine and human intraepithelial cells exhibited no major differences.     

The ultrastructural response to loading of the oral mucosa of the vervet monkey

The ultrastructural changes occurring within the epithelium of the palate, attached gingiva, tongue, buccal mucosa, and alveolar mucosa of the vervet monkey when a mechanical load was applied to the tissues was examined. The effect of the load was assessed in terms of changes in epithelial cell and nuclear shape, intracytoplasmic structures, cell membrane interdigitation, intercellular space, and changes in the shape of non-keratinocytes found within the epithelium. Loading produced a flattening of cells and nuclei throughout the epithelium. Intercellular space was reduced, cell membranes were flattened or else underwent increased interdigitation, tonofilaments became functionally oriented, and cytoplasmic vacuolation took place. The mitochondria appeared unchanged on loading. These changes were more marked in the nonkeratinized buccal and alveolar mucosa than in the keratinized palate, tongue, and attached gingiva. A histometric analysis which was carried out on the normal and loaded attached gingiva and alveolar mucosa revealed that the cells and nuclei of both tissue types underwent a significant change in width when loaded. Loading produced no significant change in the diameter of mitochondria in the basal and spinous layers.     

The nature of the granules within sulcular epithelial cells

An ultrastructural, cytochemical, autoradiographic and radioisotopic uptake study has been made of the sulcular epithelium in an attempt to explain the function of the prominent Golgi apparatus and the associated membrane bound granules which are found in the cytoplasm of the sulcular epithelial cells. Some of the granules appear to be lysosomal in nature in that they are acid phosphatase positive and in some instances they appear to release their hydrolytic enzymes into the intercellular space. The evidence presented suggests that many of the remainder of the granules are related to the production of materials which become incorporated into the extraneous cell surface coat of the epithelial cells. The radioisotope experiments suggest that the rate of synthesis of cell coat material is higher in the sulcular epithelium than it is in the oral epithelium     

Ultrastructural observation on Langerhans cells in the rat gingival epithelium

The present study was carried out to investigate ultrastructurally Langerhans cells in the rat gingival epithelium. The gingivae of lower incisors of 15 Wistar rats were examined by electron microscopy. The results were as follows: Langerhans cells were observed mainly in the lower prickle-cell layer of the gingival epithelium. On rare occasions Langerhans cells were also found in the basal and granular layers. The average number of Langerhans cells per 100 cells in the prickle-cell layer was 1.0 cell. Usually Langerhans cells had clear cytoplasms and convoluted or indented nuclei, although sometimes the cells exhibited round nuclei. The clear cytoplasm contained a moderately developed Golgi apparatus and a small number of rough surfaced endoplasmic reticulum, free ribosomes, mitochondria, and lysosomes, but it lacked tonofilaments. Birbeck granules were often found in close vicinity of the Golgi apparatus. The average number of Birbeck granules per one Langerhans cell was 4.3 granules. The cell membrane of Langerhans cells had no junctional complexes like desmosomes. The degeneration of keratinocytes adjacent to Langerhans cells was observed in a few specimens.     

Intraepithelial expression of perlecan, a basement membrane-type heparan sulfate proteoglycan reflects dysplastic changes of the oral mucosal epithelium

BACKGROUND: Intercellular deposition of perlecan, a major heparan sulfate proteoglycan (HSPG) of the basement membrane, is known to result in characteristic stellate reticulum-like structures in ameloblastomas or tooth germs. Although enlargement of the intercellular space is one of the histological characteristics of epithelial dysplasia of oral mucosa, the mode of expression of perlecan is poorly understood in these epithelial lesions. METHODS: Eighty-two biopsy specimens consisting of normal and hyperplastic epithelium, epithelial dysplasia, and squamous cell carcinomas were examined for both perlecan core protein and heparan sulfate (HS) chains by immunohistochemistry and in situ hybridization. RESULTS: In normal and hyperplastic epithelium, perlecan core protein and HS chains were localized in the cell border of parabasal cells and lower prickle cells, and HS chains were also found in basal cells. With an increase in the severity of epithelial dysplasia, the core protein was heavily and extensively deposited in the interepithelial space as well as in the cytoplasm of epithelial cells from the basal to the surface layers. Its gene expression was confirmed in the cells around the protein deposits. On the other hand, HS chains were enhanced in mild dysplasia, but decreased in moderate and severe dysplasias. In squamous cell carcinomas, either the core protein or HS chains were found scarcely in tumor cells but abundantly in the stromal space. CONCLUSIONS: The findings indicate that perlecan is localized in the intercellular space of the oral epithelia, and that it is over-expressed in dysplastic epithelial cells and is deposited in their interepithelial space, which results in the histology of reduction of cellular cohesion.     

Interepithelial cells of the oral mucosa Light and electron microscopic observations in germfree, specific pathogen-free and conventionalized mice

Abstract Interepithelial cells are found in all epithelia of the internal and external surfaces of the mammalian body. The regional differences of these Interepithelial cells and their function are not completely known so far. The quantitative and qualitative changes of the interepithelial cell population were investigated in germfree, specific pathogen-free and conventionalized mice by light and electron microscopy. Germfree and specific pathogen-free animals did not show significant differences in the number of interepithelial cells. In the epithelium of the tongue a mean of 7.4 cells per 1000 basal cells is found. After conventionalization a significant increase to 14.4 interepithelial cells per 1000 basal cells is observed. The number of cells in the buccal epithelium is constantly about 20% higher than in the epithelium of the tongue. In the oral mucosa lymphocytes, cerebriform cells and Langerhans cells are an integral component of the epithelium. In contrast to the monostratified intestinal mucosal epithelium, which is considered a secondary lymphatic tissue, the interepithelial lymphocytes of the oral mucosa are not significantly decreased in germfree animals. This could indicate that the oral mucosa functions partly as a primary lymphatic tissue. Interepithelial cerebriform cells and Langerhans cells increased after conventionalization with a maximum after 10 days in response to exogenous antigens. Both cells are immunologically important. The observations prove that the oral mucosa represents a local immunologic system in which the Langerhans cell plays an important part by formation a reticulo-epithelial tissue.     

A possible CD1a Langerhans cell–mast cell interaction in chronic hyperplastic candidosis

AIMS: T lymphocyte-antigen-presenting cell (APC) interaction plays a central role in T lymphocyte activation and APC maturation. We therefore studied the CD1a-positive Langerhans cells with respect to receptor activator of nuclear factor kappa B ligand (RANKL)-positive cells in chronic hyperplastic candidosis (CHC). MATERIALS AND METHODS: Tissue sections of CHC were compared with leukoplakia and healthy oral mucosa using RANKL and CD1a monoclonal antibodies in an avidin-biotin peroxidase complex protocol. Two different antigen-retrieval protocols, pepsin preincubation and Tris-EDTA heat treatment, were used. RESULTS: CD1a-positive Langerhans cells were in healthy and leukoplakia epithelium found in the middle layer, but in CHC in all layers of the epithelium, at the basement membrane and as mononuclear round cells in the lamina propria. Use of pepsin digestion enabled studies of mast cells and their activation in the form of degranulation of RANKL. CONCLUSIONS: The numerical, morphological and topographical versatility of the CD1a-positive Langerhans cells in CHC can be clarified by dendritic cell (DC) recruitment into the epithelium. RANK-positive and RANKL-sensitive DCs have ample opportunity to interact with local T lymphocytes. Use of an optimized antigen-retrieval protocol enabled demonstration of an active engagement (degranulation) of mast cells, which represent a rapidly available source of soluble RANKL.     

Electron microscopy of normal auman gingival epithelium

Biopsies of the labial part of normal gingival epithelium were obtained from 18 females (average age of 25 years) who had performed strict oral hygiene for two weeks or more. Standardized areas of the specimens were investigated electron microscopically. All specimens exhibited parakeratosis and were free from inflammatory cells. The optical basement membrane corresponded. to the basement lamina and an intermediate layer about 0.5 to 1 micron wide, containin various fibrils at random orientation. Cell junctions in each of the epithelial layers were typical desmosomes and maculae or zonulae occludentes. The intercellular space was interpreted to be closed from outside at the epithelial surface, subdivided into numerous compartments within all epithelial strata and open against the basement lamina. Glycogen was occasionally found in cells of the upper stratum spinosum and stratum granulosum only. The transition of cells into the stratum corneum was either abrupt or more gradual. Superficial to the stratum corneum, single or several cells of considerably less density were frequently observed. Melanocytes and Langerhans cells occurred interspersed between basal and spinous cells. The ultrastructural details are discussed with reference to the existing knowledge of other squamous epithelia.     

Human vaginal epithelium and the epithelial lining of a cyst model constructed from it: a comparative light microscopic and electron microscopic study.

The light microscopic features and keratin filament distribution of human vaginal epithelium resemble those of buccal mucosa. We used vaginal epithelium to establish a human cyst model in immunodeficient mice. To strengthen the view that this experimental cyst is a suitable model to study mucosal diseases, we compared specific light microscopic and ultra-structural features of vaginal epithelium and the epithelial lining of the cyst. Nineteen cyst walls and 6 specimens of vaginal mucosa, which had been used to establish the cysts, were examined. We counted the number of cell layers of 17 cyst linings and the 6 vaginal specimens. Surface keratinisation was evaluated on sections stained with the Picro-Mallory method. To demonstrate intercellular lamellae and membrane coating granules 2 cyst linings were examined ultra-structurally. The epithelium lining of the cyst wall was thinner than that of vaginal mucosa but the surface keratinisation and ultra-structural features of the intercellular lamellae and membrane coating granules were similar. We concluded that vaginal mucosa is a useful substitute for oral mucosa in the cyst model.     

Expression of CDIa on monocytes cultured with supernatants from periodontally diseased gingival epithelial cells

OBJECTIVE: Langerhans cells are believed to originate from the monocyte lineage and have been reported to increase in number with plaque accumulation and gingival inflammation. The aim of this study was to investigate the effects of local gingival epithelial factors on the induction of CDla, a Langerhans cell phenotype, on monocyte rich populations.
MATERIALS AND METHODS: Peripheral blood monocyte rich populations from healthy subjects were cultured for 24 h with either healthy gingival or periodontally diseased gingival epithelial supernatants. Additionally, the monocyte rich populations were cultured with cytokines IL-Iα, IL-Iβ, IL-6 and TNF-α which are known to be produced by epithelial cells or co-cultured with autologous epithelial cells. The percent CDIa positive cells was determined using FACS analysis.
RESULTS: Healthy gingival supernatants did not induce CDIa expression in monocyte rich populations, however, a significant increase in per cent CDla⁺ cells for monocyte rich populations cultured with five (P < 0.01) of six periodontal gingival epithelial supernatants was found. IL-lα or TNF-α (10ng/well) resulted in a significant increase in the per cent CDla⁺ cells (P < 0.01). Depletion of CDla⁺ Langerhans cells from healthy gingival epithelium did not enhance induction of CDIa expression in monocyte rich populations. Monocyte rich populations cultured together with non-depleted epithelial cultures resulted in a decreased percent of CDla⁺ cells.
CONCLUSION: These findings indicated that epithelial factor/s associated with periodontally involved epithelia, may be involved in inducing a Langerhans cell phenotype in monocyte rich populations. The data also provide indirect evidence for a role of Langerhans cells in inhibiting induction of CDIa in healthy epithelium.     

Ultrastructure of intra-epithelial nerve endings in the hard palate of the rat, Rattus norvegicus

The ultrastructure is described of lanceolate and free nerve endings within the epithelium of the papillae of the intermolar palatal rugae, located either between the basement membranes and the bases of the epithelial cells, or suprabasally in the intercellular spaces of the epithelium. Cytoplasmic processes of epithelial cells invaginated the Schwann cells of the nerve endings; junctions between, or fusion of, the cell membranes of the epithelial cells and the Schwann cells were not found. The neurites of the nervous structures were characterized by numerous mitochondria, clear-cored vesicles and an axoplasmic reticulum. In lanceolate endings, asymmetric membrane densities existed between the neurite and its Schwann cell, the Schwann cell showing signs of pinocytotic activity at all sides of its plasma membrane. The basal lamina of the Schwann cell covering of the nerve endings appeared to be continuous with the basal lamina of the epithelium.     

Langerhans cells: structure, function and role in oral pathological conditions

Langerhans cells (LCs) are dendritic bone marrow derived cells situated suprabasally in most stratified squamous epithelia, such as the epidermis and the epithelium of oral mucosa, including the gingiva. Langerhans cells are thought to act as antigen-presenting cells (APC) during induction of immune responses. The exact role of Langerhans cells in the oral mucosa is not fully understood although several investigations suggest that these cells are involved in reactions to antigen challenge under both normal and pathological situations. In this paper the structure, phenotypic markers and derivation of Lungerhans cells are reviewed. In view of recent findings, the immunological characteristics and the implications of Langerhans cells in pathologic oral reactions are discussed.     

Ultrastructure of rat oral epithelium in long-term cell culture

abstract — The purpose of the present study was to describe the ultrastructural appearance of squamous epithelium formed in vitro . The epithelium was formed by outgrowing cells from original explants of rat oral mucosa. Fifty-four explants from the lower surface of the tongues of 12 rats were cultured in a modified Eagle's basal medium, pH 7.2, at 32°C for up to 110 d. Subsequently the cells were prepared for electron microscopic examination. Epithelium from the lower surface of the tongues of eight rats served as control material. The in vitro specimens consisted of an extremely flattened stratified squamous epithelium. The basal cells varied from those of the control specimens by the lack of distinct bundles of tonofibrils. The intermediate cell layer exhibited a marked decrease in the number of organelles and an increase in the number of tonofilaments. No lamellated bodies or keratohyalin granules were found. The intercellular spaces were usually narrow with only a few, small desmosomes, which showed a simplified structure. The superficial cell layers showed, as did the corresponding cells of the control tissue, a distinct keratin pattern and an electron dense cytoplasmic zone along the cell membrane. It is concluded that rat oral epithelial cells grown in long-term cell culture are able to form a differentiating squamous epithelium.     

An ultrastructural study of proliferative gingivitis

Proliferative gingivitis was studied by electron microscopy. The crevicular epithelium adjacent to inflamed gingival connective tissue was primarily characterized by its relatively larger intercellular spaces which contained a variety of emigrating cells and granular precipitates resembling plasmic substances. Neutrophils and lymphocytes migrated between epithelial cells so that the intercellular spaces enlarged. The interruption of basement membrane was associated with inflammatory cells. Among the inflammatory cells plasma cells were predominant and displayed a variety of morphological characteristics. They consisted primarily of tightly packed, flattened cisternae of rough endoplasmic reticulum (rER) and a prominent paranuclear golgi zone. Fragments of cytoplasm apparently originating from the plasma cells were lying free in the surrounding intercellular space, in which collagen fibrils were impaired, disrupted and dissolved. All of these changes in plasma cells may relate to the synthesis and release of antibody. It is suggested that the inflammatory destructive features in connective tissue were mainly contributed to plasma cells.     

Histochemical localization of hyaluronate in human oral epithelium using a specific hyaluronate-binding probe.

Biochemical data suggest that gingival epithelium contains hyaluronate, but there is little histochemical information about its localization. Hyaluronate was here visualized in gingival and buccal mucosa using a specific probe derived from the hyaluronate binding region of cartilage proteoglycan. Hyaluronate was found both in the gingival and buccal epithelium, but its localization was correlated with the type of keratinization. In the keratinized epithelium of gingiva, whether ortho- or parakeratotic, the intercellular spaces from basal to upper spinous layers displayed strong staining, most intense in the middle spinous cell layer. The uppermost vital cell layers as well as the cornified cell layer remained unstained. In the non-keratinized epithelium of buccal mucosa and the local non-keratinized areas of gingiva, only the basal cells and the lowermost spinous cell layers stained for hyaluronate, whereas the majority of the upper epithelium was negative. Electron microscopic examination of the basal and spinous cell layers displayed hyaluronate, both associated with the cell surface and free in the intercellular space. The subepithelial connective tissue showed positive but diffuse staining in all specimens.     

The human gingival indeterminate cell revisited

Abstract— Electron microscopic examination of over 100 dendritic cells in human keratinized gingiva has shown that the indeterminate cells are not a separate cell type. This approach disclosed the sources of error which have led to the commonly held, but erroneous, view that there exist numerous indeterminate cells in this epithelium. Two interesting differences were found between gingival and epidermal Langerhans cells. The number of Birbeck granules in the former cells can be extremely low while they occur frequently in the epidermal cells, and granules in their formative stage are commonplace in the gingival cells but rare in the epidermal cells.     

The human gingival indeterminate cell revisited

Electron microscopic examination of over 100 dendritic cells in human keratinized gingiva has shown that the indeterminate cells are not a separate cell type. This approach disclosed the sources of error which have led to the commonly held, but erroneous, view that there exist numerous indeterminate cells in this epithelium. Two interesting differences were found between gingival and epidermal Langerhans cells. The number of Birbeck granules in the former cells can be extremely low while they occur frequently in the epidermal cells, and granules in their formative stage are commonplace in the gingival cells but rare in the epidermal cells.     

Immunohistochemical demonstration of T cell subsets and accessory cells in oral lichen planus

The nature and distribution of mononuclear cells in 30 non-ulcerated lesions of oral lichen planus (OLP) was investigated, using an immunoperoxidase technique. Most of the infiltrating cells consisted of a mixture of Leu 2a+ and Leu 3a+/3b+ T cells present in the stroma. This study proved histometrically that the emigration of lymphocytes through subepithelial vessels was not selective for major subsets of T cells and subsequent migration to the epithelium was predominant in suppressor/cytotoxic T cell infiltration. HLA-DR+/DQ+ monocyte/macrophage and Langerhans cells formed a relatively minor component of the cellular infiltrates, whereas a considerable number of T cells expressed the MHC antigens. Also, the keratinocytes of the epithelium expressed only DR antigens. These results support the concept that LP is associated with lymphokine-generated inflammation induced by helper/inducer T cells or activated T cells which would include direct basal cell damage or local immunosuppression by suppressor/cytotoxic T cells. Furthermore, this study suggests that monocytes/macrophages and Langerhans cells played a role in antigen presentation, and also that keratinocytes may possess a similar function.     

Morphometric analysis of the intercellular space and desmosomes of rat junctional epithelium

To elucidate the biological characteristics of the junctional epithelium (JE) in rats, ultrastructural and morphometric studies of the gingiva in the maxillary molar regions were carried out. Morphometric analysis of three different regions of the JE and the oral epithelium (OE) led to the following results. In the apical JE, intercellular space accounted for about 23% of the total epithelial tissue. At the connective tissue interface, the space accounted for 17% of total epithelial tissue. At the enamel interface, the space accounted for 35% of total JE tissue. A large number of leukocytes were detected in the enlarged intercellular spaces. In the OE, the space accounted for about 11%. In the apical region of the JE. desmosomes occupied approximately 5% of the plasma membrane perimeter; in both the enamel and connective tissue, about 3%; and in the OE, about 5%. However, desmosome densities were approximately 14/100 μm² in the JE. while being approximately 66/100 μm2 in the OE. From these results, it is suggested that: (a) the volume of intercellular space relative to the entire JE coincides with a dynamic migration of the epithelium; (b) enlargement of the intercellular spaces in the JE causes a low incidence of desmosomes: (c) there is no physiological permeability barrier in the JE; and (d) abundant leukocytes in the intercellular spaces may play an important role in obstructing the passage of external bacteria and toxins into the tissue.     

Immunohistochemical demonstration of T cell subsets and accessory cells in oral lichen planus

The nature and distribution of mononuclear cells in 30 non-ulcerated lesions of oral lichen planus (OLP) was investigated, using an immunoperoxidase technique. Most of the infiltrating cells consisted of a mixture of Leu 2a+ and Leu 3a+/3b+ T cells present in the stroma. This study proved histometrically that the emigration of lymphocytes through subepithelial vessels was not selective for major subsets of T cells and subsequent migration to the epithelium was predominant in suppressor/cytotoxic T cell infiltration. HLA-DR+/DQ+ monocyte/macrophage and Langerhans cells formed a relatively minor component of the cellular infiltrates, whereas a considerable number of T cells expressed the MHC antigens. Also, the keratinocytes of the epithelium expressed only DR antigens. These results support the concept that LP is associated with lymphokine-generated inflammation induced by helper/inducer T cells or activated T cells which would include direct basal cell damage or local immunosuppression by suppressor/cytotoxic T cells. Furthermore, this study suggests that monocytes/macrophages and Langerhans cells played a role in antigen presentation, and also that keratinocytes may possess a similar function.