Some new ultrastructural aspects on human epidermis and its Langerhans cells

Human epidermal energy metabolism is functionally anaerobic

We have reported that epidermal Langerhans cells possess an H(+)-extruding mechanism signalling their existence in an anaerobic environment. This study highlights the energy metabolism of human epidermis. In their habitual state the keratinocytes contain more lactate than do most other cell types. Their lactate production in vitro is vigorous and independent of oxygen and most of it is released to the medium. Autoincubation of the epidermis under starved conditions resulted in a 30% increase of lactate, indicating ongoing glycogenolysis. Iodoacetate inhibited lactate production by > 90%. Energy charge values were low, approximately 0.82, and comparable with those previously reported for smooth muscle. Moreover, the overwhelming majority of the keratinocytic mitochondria had an appearance markedly deviating from those in the Langerhans cells, melanocytes and fibroblasts, and, above all, were characterized by an enormous reduction of the inner membrane. This structure is in all probability incompatible with an effective oxidative metabolism of glucose. We conclude that epidermal energy metabolism is predominantly anaerobic in spite of the formal presence of mitochondria. The high production of lactate obviously demands extracellular transport pathways for rapid elimination of this organic acid. An extracellular space complying with such a demand emerges on electron microscopy when an isotonic glutaraldehyde-based fixative is used. The prevailing view regarding the size of the extracellular space is based on the common use of hypotonic fixatives, such as Karnovski's fixative, which causes gross cellular swelling and concomitant near total elimination of the extracellular space, leaving interstices with a diameter significantly smaller than that allowing fluid flow.

Epidermal Langerhans cells in the terrestrial turtle, Kinosternum integrum

In mammalian epidermis, Langerhans cells (LC) are the only antigen-presenting dendritic cells that possess the ectoenzyme adenosine triphosphase (ATPase) and constitutively express class II molecules encoded by the major histocompatibility complex. Recently, we demonstrated the presence of LC in chicken epidermis. The aim of the present study is to demonstrate the presence of LC-like cells in turtle Kinosternum integrum, epidermis by light and ultrastructural ATPase histochemistry. ATPase-positive dendritic cells were observed in epidermal sheets whose maximum mean number was 192 cells/mm2. Electron microscopy for ATPase stained sections showed an electrondense precipitate in the plasma membrane of dendritic clear cells located among basal and suprabasal keratinocytes, ultrastructurally similar to LC. In serial sections, some dendritic cells showed LC (Birbeck) granules. The present study demonstrates for the first time ATPase-positive dendritic cells, morphologically similar to LC, in reptilian epidermis.

Cytomembrane-derived Birbeck granules transport horseradish peroxidase to the endosomal compartment in the human Langerhans cells

It has been previously shown that the cytomembrane of human Langerhans cells (LC) has the capacity to fold upon itself, thereby forming Birbeck granules (BG), which then internalize. I confirmed this by exposing LC in vitro to horseradish peroxidase (HRP) at +8 degrees C and +37 degrees C. On incubation at +37 degrees C the label appeared not only in BG, but also in tubular structures and vesicles of different shapes and sizes. Interconnections between these labeled endosomal structures were common. The LC cytomembrane could form BG at +8 degrees C and, moreover, the BG was the only organelle that was labeled and internalized at this temperature. Thus, cytomembrane-derived BG are endocytotic in nature and link the exterior of the cell and the endosomal compartment. The membrane interlinking of the BG may eventually dissolve and the BG then transform into an endosomal vesicle.

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).

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.

Distribution of Langerhans cells in clinically healthy human gingival epithelium with special emphasis on junctional epithelium

Twenty-one biopsies of clinically healthy marginal gingiva from children, who performed conventional oral hygiene but received no additional professional prophylaxis, were studied in order to obtain information on distribution and density of Langerhans cells (LC) in the oral gingival epithelium (OGE), the sulcular epithelium (SE) and the junctional epithelium (JE). A simple freeze-separation technique was found to create acceptable histomorphology of JE in specimens obtained adherent to teeth, while partially and non-adherent ones were rejected. The majority of LC in OGE were highly dendritic and stained intensively with OKT6 monoclonal antibodies. The distribution was network-like with a density of 21.0 +/- 3.2 LC/0.1 mm2 cross-sectional epithelial area. A similar although less dense distribution was found in SE (8.6 +/- 3.0 LC/0.1 mm2). These observations confirm previous findings. In JE 2 groups of LC were identified: 1) Weakly stained LC with very few and short dendrites distributed in a scattered way (2.8 +/- 1.4 LC/0.1 mm2) in the apical three-fourths of JE in most specimens. Present evidence suggests that these cells might be immature cells of Langerhans lineage. 2) Clusters of LC (9.4 +/- 2.9 LC/0.1 mm2) with dendrites of moderate lengths and numbers and a varied fluorescence intensity; they were found in a few specimens in the coronal one-fourth of JE and at the border zone to SE. Such clusters might represent genuine variation in the distribution of LC or reactions to initial/early plaque formation.

New views on the construction of human gingival epithelium

The effects on the basal and spinous layers of human keratinized oral epithelium of 2 glutaraldehyde-based fixatives with buffers hypoosmolar and isoosmolar to blood, respectively, have been investigated. The first-mentioned solution produced an electron microscopic image corresponding to the classical view, that is an epithelium consisting of closely-packed cells having short and stubby membrane projections and separated by an extremely narrow intercellular space. In the Langerhans cells, the specific granules appeared racket-shaped and had a unilaminar limiting membrane with a periodic structure along its internal face. There are strong reasons to believe that these morphological characteristics are swelling artifacts. The last-mentioned fixative produced keratinocytes provided with numerous microvilli and membrane ruffles and disk-shaped Langerhans cell granules surrounded by a trilaminar membrane. Concomitantly, the intercellular space appears very wide and there is evidence for the view that this is a more realistic picture of the in vivo situation and not a gross distortion caused by shrinking during the tissue processing. Broad interstices can explain certain basic events as rapid cell motility within the epithelium and offer efficient pathways for rapid transport of substances.

Evaluation of in vitro predictive tests for irritation and allergic sensitization

Investigations of in vitro procedures to predict the potential of substances as skin irritants and as allergens inducing delayed hypersensitivity (contact dermatitis) are described, with indications of possible advances and known limitations. The examination of keratome slices of skin for release of enzymes, for changed histochemistry and for utilization of radioisotope-labelled amino acids will detect weak irritants but is of doubtful value for moderate irritants and will detect corrosive substances only through their inhibition of all cell activities. Fibroblast cultures, tested with Clostridium perfringens toxin and chemicals, show similar limitations in detecting moderate or severe irritants. Fibroblast cultures can be made more relevant to epidermal exposure by an overlying layer of agar containing keratin. In vitro tests to detect induction of sensitizing potential for delayed hypersensitivity have made little progress. The most promising approach is to treat antigen-presenting Langerhans cells with antigen and co-culture with lymphocytes. The lymphocytes may be examined for changes in receptor expression, for synthesis of interleukin 2, and possibly for responses to allergen if sufficient cells become specifically sensitized. There are several in vitro techniques to detect responses of in vivo- or in vitro-sensitized lymphocytes treated with antigen.

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.

Dendritic cells and monocytes as accessory cells in T-cell responses in man. I. Phenotypic analysis of dendritic cells and monocytes

A method is described for simple and rapid preparation of human dendritic cells (DC) and monocytes (Mo) from peripheral blood. The phenotype of enriched DC and Mo was determined and compared by means of a panel of monoclonal antibodies (Mab's). The distribution and quantitative expression of HLA class II molecules encoded by the subloci DP, DQ, and DR were the same on the two cell types. During in vitro culture a rapid decrease of class II antigens on Mo was observed, whereas the expression of class II antigens on DC was relatively stable. The absence of monocyte markers on DC may indicate that this cell type does not belong to the monocyte/macrophage cell lineage. The phenotypic analysis shows that peripheral blood DC also lack differentiation antigens expressed by epidermal Langerhans cells (OKT6) and lymph node follicular dendritic reticulum cells (DRC-1). The relationship between peripheral blood DC and tissue-localized DC thus remains unsolved. With relatively high numbers of DC now available, production of DC lineage-specific Mab's may be approached.