Clear and dark basal keratinocytes in human epidermis. A stereologic study

Towards a realistic dielectric tissue model: a multiscale approach

In the past, mainly analytical mixing formulas were used for modeling of dielectric properties of biological cells. General drawbacks of such formulas are the restriction to simple shapes and small cellular volume fractions. Assuming cell suspensions or tissues being quasi-periodic the problem size can be reduced to a cubic unit cell containing a single biological cell. Under this assumption numerical, e.g. Finite- Element models of such unit cells provide effective dielectric parameters for the entire tissue or cell suspension. In this work a flexible shape parametrization method allowing for a realistic representation of biological cells is applied to eight different cell types. A non-axisymmetric columnar epithelium cell occurring e.g. in the epidermis is chosen as an example. Numerical simulations of the columnar cell exposed to a time-harmonic electric field are performed for two different, high volume fractions, followed by the extraction of effective dielectric parameters of the bulk material. The simulation results are compared to two analytical approximations for ellipsoidal particles. The results suggest, that the calculation of effective dielectric properties of arbitrarily shaped cells in the frequency range between 100kHz and 1GHz requires at least a numerical cell model.

Immunohistochemical demonstration of keratin 19 expression in isolated human hair follicles

We examined keratins 19 and 8 in extracted human hair follicles using monoclonal antibodies Ks19.1 and CAM5.2, respectively. Ks19.1 reactivity was found in the bulge and infundibulum. Ks19.1(+) cells were dense in the bulge of vellus and intermediate hair follicles. The intact bulge of terminal hair could not be extracted, but the presence of Ks19.1(+) cells was confirmed in transverse sections. Infundibular Ks19.1(+) cells exhibited a dense network pattern of staining in terminal hair follicle, but only a few cells were labeled in vellus and intermediate hair follicles. CAM5.2(+) cells, i.e., Merkel cells, were found in the same locations as Ks19.1(+) cells but were less dense. These patterns of distribution and staining density were not influenced by different phases of hair cycle. Sequential staining of Ks19.1 and CAM5.2 in the same hair follicle demonstrated that the same cells could be reactive for both. However, considering the large number of Ks19.1(+) cells and rather small number of CAM5.2 in the same locations, it was assumed that only a subset of Ks19.1(+) cells are Merkel cells. It was postulated that the bulge area of human adult hair follicles houses embryonic pluripotential cells characterized by stem cells and post-stem cells and that the Merkel cells in the bulge area arise from these immature cells and may play a role in the maintenance and stimulation of this group of immature cells.

Morphometric evaluation of dark and clear epidermal basal cells during early 2-stage chemical skin carcinogenesis in the hairless mouse using two different fixation methods

Ultrastructural morphometric characteristics of basal keratinocytes in hairless mouse epidermis were analyzed statistically. The following variables were assessed: (i) low versus physiological osmolality during fixation, (ii) alterations induced by a 2-stage carcinogenesis regimen using DMBA and TPA, (iii) criteria for a cell being dark versus being clear, (iv) inter-observer variation. The results show that with low fixation osmolality most basal cells swell and become electron lucent. The few cells which apparently do not swell stand out as shrunken electron dense dark cells. Morphometrically they are more differentiated than clear cells, but do share many features with the basal cell type which appears after fixation in a buffer of physiological osmolality. Iso-osmolality during fixation seems to induce a homogeneous basal cell population of relatively electron dense cells without typical dark and clear elements. Treatment with DMBA/TPA induces not only intercellular edema and reduced desmosomal contacts, but causes injury to the plasma membrane leading to hydropic changes in the cells. This general intra- and intercellular DMBA/TPA induced hydration might induce secondary compression of some of the cells, leading to an increased number of compressed dark cells. It is, however, only after fixation in low buffer osmolality that these effects of DMBA/TPA are statistically significant and clearly observable. The inter-person variation was, apart from a few instances, either not statistically significant or did not interfere with the other effects. We did not find clear arguments in favor of the view that dark cells are primitive epidermal stem cells. They seem only to reflect non-specific toxic effects of tumor promoters, which appear only under certain fixation conditions, that have been used by most authors. The results suggest that dark and clear cells are mainly a consequence of the degree of cellular hydration.

Changes in basal cell subpopulations and tissue differentiation in human epidermal cultures treated with epidermal growth factor and cholera toxin

Cell kinetic studies on cultured human epidermal cells have indicated that cycling basal cells may be divided into at least two subpopulations that seem to differ with respect to the rate of DNA replication. The present study was undertaken in order to elucidate the biological significance of these subpopulations. The proliferation characteristics of cultured basal cells were changed by the addition of epidermal growth factor (EGF) and cholera toxin to the culture medium. It was shown that EGF and cholera toxin stimulated the growth of human epidermal cells in culture. Simultaneously, the terminal differentiation of the cells was inhibited resulting in a reduced multilayering and a reduced formation of the cornified envelope. However, only minor differences in the protein synthesis pattern were observed between cultures maintained in the presence or absence of the growth stimulators. The effect of EGF and cholera toxin on the basal cell subpopulations was investigated after 3H-thymidine labelling followed by cell sorting and autoradiography. In the presence of EGF and cholera toxin dramatic changes were induced in the labelling pattern of sorted S-phase cells indicating significant alterations in the balance between the subpopulations of cycling basal cells. Our results with these substances are in accord with the hypothesis that the observed cell kinetic subpopulations may be related to regeneration or early events in the differentiation process of the keratinocyte.

Psoriasis: maintenance of an intact monolayer basal cell differentiation compartment in spite of hyperproliferation

Frozen sections of punch biopsies from normal epidermis and psoriatic involved and uninvolved epidermis have been examined immunocytochemically using a panel of anti-keratin monoclonal antibodies with various specificities in the skin. Since psoriasis is thought to involve hyperproliferative expansion of the basal compartment from one to about three cell layers in thickness, the samples were screened with antibodies to intermediate filament determinants associated with basal cells, suprabasal cells and hyperproliferating keratinocyte-derived cell lines, respectively. The basal-suprabasal division was observed to be intact, with only one layer of basal cells demarcated by the specific antibodies used under all circumstances. This suggests that (a) psoriatic "basal cell hyperproliferation' may not specifically involve the basal cell compartment containing the stem cells, but rather a population of amplifying transit cells which are predominantly suprabasal, and that (b) while keratinocyte differentiation begins as the cells lose contact with the basal lamina, the first stages at least of differentiation are not dependent on the loss of the capacity to divide.

Possible role of apoptotic cells of the oral epithelium in the pathogenesis of aphthous ulceration

Electron microscopic examination of the normal oral mucosa of patients with recurrent aphthous ulceration or Behçet's syndrome revealed that the degenerate dark prickle cells are apoptotic cells. Such dark prickle cells showed characteristic findings of apoptosis, such as the shrinkage of nucleus and cytoplasm and the formation of contraction vacuoles. The number of intraepithelial mononuclear cells phagocytosing apoptotic cellular debris increased remarkably at the preulcerative stage of the aphthous lesions. The apoptotic debris also attracted neutrophilic leukocytes in the prickle cell layer at the preulcerative stage but not in the normal oral epithelium. It is speculated that the onset of aphthous ulceration is closely related to phagocytosis of these apoptotic cells by intraepithelial mononuclear cells.

Identification and localization of label-retaining cells in hamster epithelia

A subpopulation of basal epithelial cells which retains tritiated thymidine label for extended periods was previously demonstrated in skin and oral mucosae of mice. The present study examined the presence of similar cells in hamsters. Five-day-old hamsters were labeled with tritiated thymidine and the rate at which label was diluted from the basal cells observed. A small percentage of basal cells was found to retain label for up to 69 days. The location of such label-retaining cells ( LRCs ) in the palatal epithelium and in tongue papillae was examined. Thirty and 69 days after labeling, approximately 80% of LRCs in palate were located in the proximal halves of papillae and 80% of LRCs in tongue were positioned basally with approximately 30% of such LRCs occupying positions previously suggested to be stem cell locations. The finding that slowly cycling keratinocytes are related to patterns of tissue architecture is compatible with a function of these cells as epithelial stem cells.

Morphologic investigations on the rebound phenomenon after corticosteroid-induced atrophy in human skin

Cutaneous atrophy was induced on the forearms of 4 volunteers by continuous occlusive application of clobetasol-17-propionate for 6 weeks, after which time the steroid was discontinued. Epidermal and dermal changes during the subsequent rebound "flare" were monitored for 2 weeks by light and transmission electron microscopy. An exuberant hyperplasia characterized the epidermal response. Within 2 days poststeroid, most basal cells displayed fine structural features typical of highly proliferating cells. "Dark"-staining keratinocytes appeared in large numbers 4 days poststeroid, preceding a 4-fold maximal increase of viable epidermal thickness which occurred at 7 days. The stratum corneum, initially very thin, increased markedly in thickness and displayed the typical basket-weave appearance. By 14 days, Langerhans cells, which were absent immediately poststeroid, were again present. At this time, the epidermis returned to a nearly normal state. Dermal restitution was similarly rapid. Initially, fibroblasts appeared very active as evidenced by widely dilated endoplasmic reticulum filled with flocculent material. Ground substance increased continuously, reaching normal levels by 14 days. An increase in postcapillary venules was noted during the rebound flare. Swift epidermal and dermal changes are evidence that topical corticosteroids are rapidly cleared from the skin. The vigorous epidermal hyperplasia reflects repair of the atrophic, suppressed epidermis as well as a response to desiccation consequent to the loss of the stratum corneum.

beta-Fibrillary bodies in low-grade adenocarcinoma of parotid gland: a histochemical and ultrastructural study

Rounded or polyhedral, acellular, dense lamellated structures were seen within the cystic and glandular spaces in a case of low-grade papillary adenocarcinoma of the parotid gland. These structures displayed the histochemical characteristics of amyloid, namely, pink color with apple-green birefringence and bright red fluorescence with alkaline congo red, orthochromasia and red birefringence with standardized toluidine blue, positive dimethylaminobenzaldehyde nitrite and diazotization coupling reactions, and spontaneous autofluorescence. At the ultrastructural level the tumor consisted of cuboid, flattened, or elongated epithelial cells with varying degrees of differentiation, but most mature tumor cells had numerous intracellular intermediate filaments. These filaments were randomly oriented and had no lateral fasciation; they were 10 nm wide and similar to those constituting the intraluminal corpora amylacea. These bodies displayed increased fibrillary density. Cellular organelles and pyknotic nuclei were frequently present at the periphery of the fibrillary masses. Amyloid masses, histochemically and ultrastructurally indistinguishable from those in the lumens, were present in the stroma as well. It is postulated that both stromal and intraluminal beta-fibrillary bodies result from apoptosis and desquamation of neoplastic cells, with progressive release and confluency of intracellular intermediate filaments within closed cystic spaces. This additional evidence of beta-fibrillosis associated with a slow-growing non-hormone-secreting salivary gland tumor suggests that these tumors may be associated with amyloidosis more frequently than was previously suspected.

Heterogeneity in epidermal basal keratinocytes: morphological and functional correlations

Two structurally distinct populations of basal keratinocytes, nonserrated and serrated, were observed in cynomolgus monkey and human palm epidermis. Anatomical location, fine structural features, and kinetic properties suggest that nonserrated cells represent a stem cell population and that serrated cells help anchor the epidermis to the dermis.

Skin explant cultures: expression of cytoplasmic differentiation antigens in outgrowth cells

In vivo, keratinocyte cytoplasmic antigens linked to keratinization have been traced with 2 distinct types of antibodies found in human sera. One type of antibody is specific for the basal cell compartment of keratinocytes while the other one is specific for upper keratinocytes. Using these markers, we followed a well-defined, in vitro human keratinocyte culture system that produces a keratinizing epithelial cell outgrowth juxtaposed to dead dermal substrate for the in vitro expression of keratinocyte cytoplasmic antigens. These antigens were found to be expressed in vitro independently from dermal influences. Their chronology, localization and topography in culture matched the in vivo situation.