Interepithelial cells of the oral mucosa in mice. An ultrastructural classification with reflections on the origin of the Langerhans cell

Tongue immune compartment analysis reveals spatial macrophage heterogeneity

The tongue is a unique muscular organ situated in the oral cavity where it is involved in taste sensation, mastication, and articulation. As a barrier organ, which is constantly exposed to environmental pathogens, the tongue is expected to host an immune cell network ensuring local immune defence. However, the composition and the transcriptional landscape of the tongue immune system are currently not completely defined. Here, we characterised the tissue-resident immune compartment of the murine tongue during development, health and disease, combining single-cell RNA-sequencing with in situ immunophenotyping. We identified distinct local immune cell populations and described two specific subsets of tongue-resident macrophages occupying discrete anatomical niches. Cx3cr1⁺ macrophages were located specifically in the highly innervated lamina propria beneath the tongue epidermis and at times in close proximity to fungiform papillae. Folr2⁺ macrophages were detected in deeper muscular tissue. In silico analysis indicated that the two macrophage subsets originate from a common proliferative precursor during early postnatal development and responded differently to systemic LPS in vivo. Our description of the under-investigated tongue immune system sets a starting point to facilitate research on tongue immune-physiology and pathology including cancer and taste disorders.

Ultrastructural examination of experimentally induced premalignant lesions

Lesions induced in hamster cheek pouch using dimethylbenz(alpha)anthracene were studied by transmission electron microscopy and compared with normal tissue. Features regarded as suggestive of progression towards malignancy were: increased numbers of membrane-bound vesicles in basal cells, gaps in the lamina densa associated with widening of the lamina lucida and an irregular epithelial-connective tissue junction, the presence of cerebriform cells and frequent close association of 2 or more intra-epithelial cells (lymphocytes, cerebriform cells, Langerhans cells).

Extent and diversity of inflammatory cell infiltrates in squamous cell carcinomas and basal cell epitheliomas of the head and neck

Using monoclonal antibodies reactive with Langerhans' cells (LCs), macrophages, and T cell subpopulations, the density and proportions of cells of the immune system of the normal oral mucosa were determined immunohistochemically, and compared with findings in oral squamous cell carcinomas (SCC) and basal cell epitheliomas (BCE). In normal oral epithelia, the dominant cell type was the LC, positive for CD 1, and expressing HLA-DR antigens (DR+). Many intraepithelial cells were lymphocytes of the suppressor/cytotoxic phenotype (CD 8+), which was also the most prominent cell type in the normal mucosal stroma. Significant differences were observed for the content of CD 8-, OKM 1-, and CD 4-positive cells in the epithelium of normal oral mucosa, SCC, and BCE, and for the amount of CD 1-positive Langerhans cells in the connective tissue of the different groups of tissues. When CD 4/CD 8 ratios were calculated, differences between SCC and BCE became most evident. A CD 4/CD 8 ratio greater 0.5 was seen to be characteristic for BCE. Thus, in contrast to the striking preponderance of suppressor/cytotoxic lymphocytes (CD 8+) in SCC, BCE showed typically almost balanced numbers of suppressor/cytotoxic (CD 8+) and helper/inducer (CD 4+) lymphocytes. This finding further underlines the biological differences recognized between these most common neoplasias of the head and neck.

The ultrastructure of human gingival Langerhans cells in health and disease

There was a statistically significant shift towards increased proportions of type I Langerhans cells (containing many Langerhans-cell granules) and reduced proportions of both type II Langerhans cells (containing few granules) and indeterminate cells in diseased oral epithelium when compared to healthy oral epithelium. Langerhans cells and indeterminate cells were also seen in the sulcular epithelium of healthy and diseased specimens but never in junctional or pocket-lining epithelium.

The ultrastructure of initial changes in hapten-exposed rat oral mucosa

The experimentally induced cell-mediated immune reaction has been examined ultrastructurally in rat oral mucosa, using DNCB/DNFB as haptens. In skin-presensitized animals, an increased number of mononuclear cells was found in the epithelium at a very early phase (15-60 min) after hapten exposure. In nonsensitized animals, an increased number of cells was evident in hapten-exposed tissue also very early in the reaction. Mononuclear cells appeared in the connective tissue but very few in the epithelium. Interaction between mononuclear cells and Langerhans cells could be demonstrated in both experimental groups.

Identification of Langerhans cells in human gingival epithelium

The purpose of this study was to qualitatively compare three recent techniques of Langerhans cells detection in oral epithelium and to quantitatively compare Langerhans cells in clinically normal and clinically inflamed human gingival biopsies. Eleven subjects were selected who displayed chronic periodontitis and moderate gingival inflammation. A quadrant associated with clinically inflamed tissues was not treated, while the remaining teeth were scaled and root-planed. Two gingival biopsies were taken: clinically normal, treated tissue; and clinically inflamed, untreated tissue. Langerhans cells were stained using HLD-DR, S-100 and OKT6. They were quantitated using a standard grid for OKT6-stained sections only. Approximately 5 times as many Langerhans cells were identified in the biopsy specimens of clinically inflamed human gingiva as in clinically normal gingiva of the same patient. Of the methods studied, OKT6 was qualitatively determined to be the best for visualization of these cells. An immunologic role in the host response to chronic periodontal disease is postulated for Langerhans cells.

Quantitative analysis of immunocompetent cells in human normal oral and uterine cervical mucosa, oral papillomas and leukoplakias

Using monoclonal antibodies reacting with T-cell subpopulations, Langerhans cells and macrophages, the number and distribution of cells of the immune system in normal oral and cervical mucosa was determined and statistically compared with that in oral papillomas and oral leukoplakias. Increased numbers of labelled cells were found in oral leukoplakias and particularly in oral papillomas. In the epithelium of all specimens, Langerhans cells and T-lymphocytes of the suppressor/cytotoxic phenotype as well as of the helper phenotype were seen. Suppressor/cytotoxic and helper T-lymphocytes were in equal numbers in the epithelium of oral papillomas, but were about 2:1 in all other lesions. In normal oral epithelium, macrophages were rare but were in greater numbers in leukoplakias and papillomas. In the connective tissue of all lesions, more labelled cells were present than in epithelium with T-lymphocytes predominant. Although Langerhans cells were rare in connective tissue, many were seen in oral papillomas.

Langerhans cells: antigen presenting cells of the epidermis

While epidermis in the skin provides an excellent barrier to the environment, it is an incomplete one. Some antigenic material can penetrate through the stratum corneum (or be introduced pathologically) where strategically placed epidermal Langerhans cells reside. In this review, we have assembled relevant data concerning the antigen presenting potential of epidermal Langerhans cells. Strong circumstantial evidence derived from in vitro studies of epidermal cell suspensions enriched for Langerhans cells indicates that Langerhans cells possess this capability. In vivo studies with intact skin indicate that critical numbers of functioning Langerhans cells are essential for successful induction of contact hypersensitivity by epicutaneously applied haptens. And within the past several months, experiments with purified preparations of epidermal Langerhans cells have proven that these cells, and perhaps they alone among epidermal cells, possess the capacity of processing and presenting haptenic determinants to the immune system. The challenge for the future is to determine the extent to which this unique property of Langerhans cells affords physiologic protection to the skin and under what pathologic circumstances altered Langerhans cell function leads to disease.

Recent advances in oral mucosal research

Major progress in investigation of the normal structure and function of the oral mucosa has been made within the last ten years and has come principally from the application of various techniques developed in basic science disciplines to specific mucosal problems. However, it is apparent that many gaps still exist in our knowledge of the oral mucosa and, although it is to be expected that different workers will have distinct views on which of these are the most significant, some basic areas for further investigation can clearly be identified. For example, little is known about epithelial control systems and their disturbance by epithelial disease processes, about the nature of the interactions occurring during development and maintenance of the oral mucosal epithelia, or about the epithelial cell surface and its role in normal function. The specific properties and behavior of the cell populations of the subepithelial connective tissues appears to be poorly understood and the existence and significance of functional changes in mucosa with age and malnutrition are uncertain. It is increasingly apparent that successful progress in such investigations involves approaches using diverse methodologies. For example, epithelial-mesenchymal interactions are likely to involve multiple mesenchymal factors acting in concert to establish and maintain epithelial form and, because of this complexity, the nature of the inductive influences is not likely to be elucidated in model systems unless individual variables can be rigidly controlled. Defining the cellular and acellular elements in mesenchyme and reconstructing a functional mesenchyme from purified components may not be a simple task, but with current methods for cultivating mucosal keratinocytes and fibroblasts, as well as for purifying various components of the ground substance, it should be possible to initiate such a program of study. Some of the most dramatic advances made over the past 5-6 years in epidermal research have come about through the utilization of newly developed biochemical investigative techniques, examples of which include the use of gene cloning to study the organization of the keratin gene family, and the use of immuno-fluorescence with monoclonal antibodies to discern when various keratin proteins appear during differentiation.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of inflammatory cell phenotypes in human oral carcinomas by means of monoclonal antibodies

Monoclonal antibodies reacting with human T cell sub-populations, Langerhans cells and macrophages were used to examine the quantitative distribution of immune-competent cells in normal oral mucosa and invasive oral carcinomas. Both immunofluorescent and immunoperoxidase procedures were applied. In normal oral epithelia, the dominant immune-reactive cell was the Langerhans cell, positive for OKT 6 and expressing HLA-DR gene products (OKIa1+). Many intra-epithelial non-epithelial cells (non-keratinocytes), belonged to the lymphocyte system carrying the suppressor/cytotoxic phenotype (OKT 8+). This lymphocyte sub-population was also the most prominent cell type in the normal mucosal stroma. The quantitative evaluation of immune-competent cells in squamous cell carcinomas revealed elevated numbers of all the inflammatory cell sub-populations investigated (suppressor/cytotoxic lymphocytes, helper/inducer lymphocytes, Langerhans cells, macrophages) compared with the normal oral mucosa. There was a striking increase in suppressor/cytotoxic lymphocytes (OKT 8+) and in cells of the macrophage system, including Langerhans cells (OKIa1+, OKM 1+, OKT 6+). In the stroma distant to the tumour complexes, many helper/inducer lymphocytes (OKT 4+) were also observed.

Association between plaque accumulation and Langerhans cell numbers in the oral epithelium of attached gingiva

After gingival health had been achieved in four subjects they were instructed to cease all oral hygiene measures. At 0, 8 and 21 days Plaque and Gingival Indices were recorded and gingival biopsies were removed from the buccal aspect of a first molar. Frozen sections of the gingival oral epithelium were stained for ATPase and 5'-nucleotidase to determine the number of Langerhans cells in a defined cross-sectional area. It was found that, as plaque accumulated, there was a statistically significant increase in the number of Langerhans cells in oral epithelium, particularly in the stratum spinosum. These results indicate that dental plaque can elicit a response in Langerhans cells located in the oral epithelium of the gingiva.

Subplasmalemmal linear density: a mesodermal feature and a diagnostic aid

Subplasmalemmal linear density (SLD), a surface structure known to occur on mononuclear phagocytes, has been considered a possible morphologic marker of mesenchymal cells or cells of mesodermal origin. A retrospective review of human surgical pathology cases studied in a diagnostic electron microscopy laboratory over a five-year period confirmed that SLDs are primarily seen in cells of mesodermal origin in a variety of neoplastic and nonneoplastic tissues. Therefore, SLD may be of value as a mesodermal marker in evaluating poorly differentiated tumors. Furthermore, the presence or absence of SLD in tissue histiocytes in diverse conditions may contribute to the understanding of heterogeneity among this group of cells.

Langerhans cells in dermoid cysts: transmission electron microscopic, cytochemical and immunofluorescent observations

Langerhans cells were detected in squamous, stratified epithelia lining human dermoid cysts. Their presence was assayed by ATPase staining and reactivity with heteroantisera against "Ia-like" antigens. Transmission electron microscopic studies demonstrated variations in the numbers of cells showing Birbeck granules in epithelia with different degrees of keratinization. Indeterminate cells (i.e. lacking granules), were more frequent in epithelia showing combined mucous and keratinizing differentiation. Membrane-coating-granules and keratohyalin granules were present in epithelia containing Langerhans cells with clearly identifiable Birbeck granules. Interepithelial mast cells were observed in epithelia with mucous differentiation. A relationship between Langerhans cells and keratinization was suggested. Such non-immune functions are compatible with the known macrophage characteristics of the cell.

Ultrastructural evidence suggesting an immunomodulatory activity of oral retinoid. Its effect on dermal components in psoriasis

The effects of the aromatic retinoid RO 10-9359 on the fine structure of psoriatic dermis were investigated by electron microscopy in five patients after 1, 2, and 3 weeks of treatment (I mg/kg/day). Our findings show that aromatic retinoid, additionally to its epidermal effects, exerts a distinct influence on dermal components in psoriasis. Ultrastructural evidence is provided suggesting that this drug stimulates lymphocytes and monocytes, promoting their differentiation into Sézary-like lymphocytic cells, activated macrophages and dermal Langerhans cells. The appearance of these immunocompetent cell lines may modulate the cell-mediated immune response in psoriasis, obviously reflecting a pharmacological action of the drug additional to its definite influence on epidermal keratinization.

Epithelial and interepithelial mitoses of the oral mucosa: light and electron microscopic study in mice after exposure to different antigens

Many epithelia respond to exogenous injurious agents with an increased proliferation. Until now interepithelial cells (neuroectodermal cells, lymphocytes, cerebriform cells and Langerhans cells) have been neglected in investigations of the proliferation kinetics of stratified squamous epithelia. In mice with different antigenic exposure, and in T-cell deficient nude mice mitoses in the oral epithelium were counted by light microscopy and the proportion of mitoses of interepithelial cells was determined by an additional ultrastructural analysis. NMRI mice raised in "germ-free" and "specific pathogen-free" environments exhibit decreased mitotic rates in lingual and buccal epithelia (16 mitoses per 1000 basal cells) when compared with mice raised in "normal" environments. NMRI mice exposed orally to Candida albicans exhibit increased mitotic rates in the same 2 epithelial sites (35 mitoses per 1000 basal cells after 2 days). Similar changes occur in athymic nude mice. The electron microscopic observations showed that most of the mitoses occurred among keratinocytes. Only sporadic mitoses of nonepithelial cells could be observed within the epithelium. However, these amounted to less than 5% of the total of mitoses. Our results show that for proliferation kinetic studies of squamous epithelia this low proportion of interepithelial mitoses may be negligible. Interepithelial cells apparently recruit mainly from migrating cells into the epithelium, while proliferation in situ plays a secondary role. As there are no signs of a transmigration of the epithelium by interepithelial cells they must be considered a recirculating cell population.

Cutaneous manifestations in rats with advanced vitamin A deficiency

Specific-pathogen-free rats kept on a vitamin A-deficient diet for approximately 5 months developed cutaneous alterations, especially in the periorbital and eyelid skin. These lesions were characterized grossly by erythema, partial alopecia, and crusting, and histologically by hyperorthokeratinization, acanthosis, and a three-fold increase in incorporation of labeled DNA precursors into the epidermal basal layer. Electron microscopy showed an increased number of Langerhans cells with and without Birbeck granules, as well as the presence of cytoplasmic dense bodies of probable lipid nature in keratinocytes of all epidermal strata. The similarities of these ultrastructural alterations with some features of vitamin A-sensitive human dermatoses point to probable common mechanisms in the pathogenesis of these skin diseases.

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

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 cells plays an important part by formation a reticulo-epithelial tissue.