Epidermal Langerhans cells contain intermediate-sized filaments of the vimentin type: an immunocytologic study

Life cycle of chicken bursal secretory dendritic cell (BSDC)

The transmission electron microscopy revealed a dendritic cell in the medulla of the chicken bursal follicle. This dendritic cell has a classical secretory machinery; therefore, it has been named a bursal secretory dendritic cell (BSDC). The corticomedullary epithelial arch (CMEA) encloses lymphoid-like cells, which can proliferate and after entering the medulla, begin to differentiate to immature, then mature BSDC, which discharges glycoprotein (gp). With the exhaustion of gp production, the BSDC rapidly transforms into a macrophage-like cell (Mal), which is an activated endocytic cell of innate immunity. The Mal drifts through the follicle-associated epithelium (FAE)-supporting cells into the FAE, and via FAE, the Mal is eliminated in the bursal lumen. The infectious bursal disease virus (IBDV) infection accelerates the maturation process of BSDC precursors, which results in acute emptying of CMEA and subsequently, numerous immature BSDC(s) emerge. The IBDV infection stops the gp discharge, and the gp appears in the virus-containing Mal. The Movat pentachrome staining recognizes the gp in the extracellular spaces of the medulla and after infection in the Mal. The BSDC is the primary target of the IBDV. During IBDV infection, a large number of suddenly formed Mal actively migrate into the cortex, initiating cytokine storm and recruiting heterophil granulocytes. During embryogenesis, the vimentin-positive, possibly embryonic dendritic cells provide a microenvironment for carbohydrate switch. Around hatching, these embryonic, temporary dendritic cells get the Fc receptor, which bind maternal IgY. The posthatched forms of BSDC(s) gradually replace the embryonic ones and bind their own IgY.

The bursal secretory dendritic cell (BSDC) and the enigmatic chB6+ macrophage-like cell (Mal)

The bursal secretory dendritic cell (BSDC) was discovered more than 40 yr ago. It is a highly polarized, granulated cell, locating in the medulla of bursal follicle. The cytoplasmic granules either discharge or fuse together forming large, irregular-shaped, dense bodies. Formation of the dense bodies could be the first sign of BSDC transformation to macrophage-like cell (Mal) which is the result of terminal maturation of BSDC. The BSDC is non-phagocytic, unlike Mal. The discharged substance may be attached to the cell membrane (membrane-bound form) and after detaching, appears as a flocculated substance in the extracellular space of medulla. Movat pentachrome staining shows, that this substance is a glycoprotein (gp), which may be contributed to the microenvironment of the medulla. Medullary lymphocytes are floating in the gp. Precursors of the BSDC locate in the corticomedullary epithelial arches, which operate under the effect of Notch/Serrate signaling. The Notch signaling determines the fate of lymphoblast-like precursor cells and inhibits the appearance of immunoglobulin heavy chain. In the arches, the precursor cells proliferate and entering the medulla differentiate. The dense bodies pack the virus particles, which prevents the granular discharge, resulting in disappearance of extracellular gp, but gp emerges inside the virus containing Mal. In infected birds, the Mal contains either apoptotic cells or virus particles. If vaccination or infectious bursal disease virus (IBDV) infection use up the BSDC precursors, the recovery of follicle is critical.

Characterisation of corneas following different time and storage methods for their use as a source of stem-like limbal epithelial cells

The transplantation of expansions of limbal epithelial stem cells (LESC) remains one of the most efficient therapies for the treatment of limbal stem cell deficiency (LSCD) to date. However, the available donor corneas are scarce, and the corneas conserved for long time, under hypothermic conditions (after 7 days) or in culture (more than 28 days), are usually discarded due to poor viability of the endothelial cells. To establish an objective criterion for the utilisation or discarding of corneas as a source of LESC, we characterized, by immunohistochemistry analysis, donor corneas conserved in different conditions and for different periods of time. We also studied the potency of LESCs isolated from these corneas and maintained in culture up to 3 cell passages. We hoped that the study of markers of LESCs present in both the corneoscleral histological sections and the cell cultures would show the adequacy of the methods used for cell isolation and how fit the LESC enrichment of the obtained cell populations to be expanded was. Thus, the expressions of markers of the cells residing in the human limbal and corneal epithelium (cytokeratin CK15 and CK12, vimentin, Collagen VII, p63α, ABCG2, Ki67, Integrin β4, ZO1, and melan A) were analysed in sections of corneoscleral tissues conserved in hypothermic conditions for 2-9 days with post-mortem time (pmt) < 8 h or for 1 day with pmt > 16 h, and in sclerocorneal rims maintained in an organ culture medium for 29 days. Cell populations isolated from donor corneoscleral tissues were also assessed based on these markers to verify the adequacy of isolation methods and the potential of expanding LESCs from these tissues. Positivity for several putative stem cell markers such as CK15 and p63α was detected in all corneoscleral tissues, although a decrease was recorded in the ones conserved for longer times. The barrier function and the ability to adhere to the extracellular matrix were maintained in all the analysed tissues. In limbal epithelial cell cultures, a simultaneous decrease in the melan A melanocyte marker and the putative stem cell markers was detected, suggesting a close relationship between the melanocytes and the limbal stem cells of the niche. Holoclones stained with putative stem cell markers were obtained from long-term, hypothermic, stored sclerocorneal rims. The results showed that the remaining sclerocorneal rims after corneal transplantation, which were conserved under hypothermic conditions for up to 7 days and would have been discarded at a first glance, still maintained their potential as a source of LESC cultures.

Epithelial to mesenchymal transition in human skin wound healing is induced by tumor necrosis factor-alpha through bone morphogenic protein-2

Epithelial-mesenchymal transition (EMT), characterized by loss of epithelial adhesion and gain of mesenchymal features, is an important mechanism to empower epithelial cells into the motility that occurs during embryonic development and recurs in cancer and fibrosis. Whether and how EMT occurs in wound healing and fibrosis in human skin remains unknown. In this study we found that migrating epithelial cells in wound margins and deep epithelial ridges had gained mesenchymal features such as vimentin and FSP1 expression. In hypertrophic scars, EMT-related genes were elevated along with inflammatory cytokines, indicating a causal relationship. To reconstitute EMT in vitro, normal human skin and primary keratinocytes were exposed to cytokines such as tumor necrosis factor-alpha (TNF-alpha), resulting in expression of vimentin, FSP1, and matrix metalloproteinases. Moreover, TNF-alpha-induced EMT was impaired by antagonists against bone morphogen proteins (BMP) 2/4, suggesting that BMP mediates the TNF-alpha-induced EMT in human skin. Indeed, TNF-alpha could induce BMP-2 and its receptor (BMPR1A) in human skin and primary keratinocytes, and BMP2 could induce EMT features in skin explants and primary keratinocytes. In summary, we uncovered EMT features in both acute and fibrotic cutaneous wound healing of human skin. Moreover, we propose that the mesenchymal induction in wound healing is motivated by TNF-alpha, in part, through induction of BMP.

Characterization of chicken epidermal dendritic cells

It has been known for 15 years that the chicken epidermis contains ATPase+ and major histocompatibility complex class II-positive (MHCII+) dendritic cells. These cells were designated as Langerhans cells but neither their detailed phenotype nor their function was further investigated. In the present paper we demonstrate a complete overlapping of ATPase, CD45 and vimentin staining in all dendritic cells of the chicken epidermis. The CD45+ ATPase+ vimentin+ dendritic cells could be divided into three subpopulations: an MHCII+ CD3- KUL01+ and 68.1+ (monocyte-macrophage subpopulation markers) subpopulation, an MHCII- CD3- KUL01- and 68.1- subpopulation and an MHCII- CD3+ KUL01- and 68.1- subpopulation. The first population could be designated as chicken Langerhans cells. The last population represents CD4- CD8- T-cell receptor-alphabeta- and -gammadelta- natural killer cells with cytoplasmic CD3 positivity. The epidermal dendritic cells have a low proliferation rate as assessed by bromodeoxyuridine incorporation. Both in vivo and in vitro experiments showed that dendritic cells could be mobilized from the epidermis. Hapten treatment of epidermis resulted in the decrease of the frequency of epidermal dendritic cells and hapten-loaded dendritic cells appeared in the dermis or in in vitro culture of isolated epidermis. Hapten-positive cells were also found in the so-called dermal lymphoid nodules. We suggest that these dermal nodules are responsible for some regional immunological functions similar to the mammalian lymph nodes.

Melanocytes in the corneal limbus interact with K19-positive basal epithelial cells

The human corneal limbus is identified by the distinct features of the palisades of Vogt (POV), which contain pigment granules that are aligned with the microplicae of the epithelium. Although it is presumed that pigments are produced by melanocytes, the characterization of melanocytes in the limbus has not been clearly documented. We examined human limbal tissues by whole mounts and serial histological sections to localize epithelial cells containing melanin granules. Most of the pigmented cells observed by immunohistochemistry were K19 (+) cells in the basal limbal epithelium. A superimposed image revealed that melanin granules were oriented towards the apex of each K19 (+) cell, acting as a pigmented cap facing the ocular surface. Melanocytes were identified by MART1, an antigen specific to melanocyte-lineage cells. Melanocytes were shown to exist as sporadic cells with dendritic processes that extend to surrounding epithelial cells. Melanocytes were also found in light-pigmented donor tissue when visualized by the tyrosinase assay using the enzyme substrate DOPA. Since tyrosinase activity was not found in epithelial cells, the production of melanin is exclusively the role of melanocytes that comprised 5.3+/-2.7% of the total cells in cytospin samples (N=3). Melanocytes and K19 (+) epithelial cells may form a functional network similar to the melanin unit of the skin.

Milestones in the research on skin epidermal Langerhans/dendritic cells (LCs/DCs) from the discovery of Paul Langerhans 1868-1989

Almost 100 years elapsed after the discovery of dendritic cells in the human skin epithelium by Paul Langerhans in 1868 until the initiation of research on those cells was reinitiated. The present paper provides the milestones in the research on Langerhans/dendritic cells (LCs/DCs) between 1960 and 1989. This historical review will explain how researchers gradually discovered the role of the bone marrow-derived dendritic cells in the immune response. The paper is an appendix to the manuscript entitled: "Immunological and regulatory functions of uninfected and infected immature and mature subtypes of dendritic cells" (Virus Genes 26: 119-130, 2003).

VML 295 (LY-293111), a novel LTB4 antagonist, is not effective in the prevention of relapse in psoriasis

Leukotriene B4 (LTB4) receptor antagonists have been the subject of several studies in the treatment of inflammatory diseases, including psoriasis. A novel oral LTB4 antagonist, VML 295 (LY-293111) has recently been developed and has a pronounced effect on epidermal inflammatory parameters. However, oral treatment of psoriasis for 4 weeks did not result in a decrease in disease severity. The present study was performed in order to investigate whether prolonged treatment with VML 295 up to 8 weeks has a beneficial effect on the overall severity of psoriasis. Moreover, we studied to what extent VML 295 is able to prevent relapse in psoriasis. In the present study, 35 patients with stable chronic plaque psoriasis were included. A representative plaque of at least 16 cm2 was initially treated with clobetasol-17-propionate lotion under hydrocolloid occlusion in all patients. Clearance was achieved within 6 weeks in 31 patients. After clearance, the patients were randomized to treatment and received oral VML 295 capsules 200 mg twice daily or placebo for 8 weeks. Twenty-five patients completed the study. The psoriasis area and severity index (PASI) was assessed before treatment, at clearance, and on days 15, 29, 43 and 5 7 of the treatment period. Biopsies were taken from the treated lesion before treatment, after clearance and at relapse, and cells were analysed by flow cytometry with markers for differentiation (keratin 10), inflammation (vimentin), and proliferation (DNA content). After 8 weeks of treatment, 14 of 15 VML 295-treated patients had relapsed and 11 of 16 placebo-treated patients had relapsed. A total of six patients were withdrawn. The time to relapse and the number of relapsed patients was not significantly different comparing the treatment groups. There was no significant difference in PASI scores between VML 295-treated patients and placebo-treated patients after 8 weeks of treatment. Flow cytometric parameters for differentiation, inflammation and proliferation did not show significant differences between VML 295- and placebo-treated patients. We conclude that oral VML 295 (LY-293111) is not effective in preventing relapse in psoriasis, either clinically or at the cellular level, and that in our group of patients VML 295 had no beneficial effect on overall psoriasis severity. Moreover, we conclude that further development of LTB4 modulating drugs for the treatment of psoriasis is not indicated.

The effect of long-term treatment with tacalcitol on the psoriatic epidermis. A flow cytometric analysis

During the last decade, novel analogues of 1alpha,25-dihydroxy vitamin D3 have been developed for the treatment of psoriasis. Recently, the efficacy of short-term treatment with the novel derivative tacalcitol (1alpha,24-dihydroxy vitamin D3) has been documented. However, data on the long-term effect of tacalcitol on psoriatic skin are sparse. In this study, we assessed the cell characteristics of the psoriatic epidermis after treatment with tacalcitol for up to 24 weeks. We investigated how long-term treatment with tacalcitol modulates the percentages of differentiated keratinocytes, inflammation cells and basal keratinocytes, and the percentage of cells in the SG2M phase in the basal cell population. From 11 patients who were treated with tacalcitol for up to 18 months, we obtained single-cell suspensions of a representative psoriatic lesion after 0, 8, 12, 18 and 24 weeks of treatment. A Psoriasis Area and Severity Index was performed at each visit as well. Cell suspensions were stained with markers for inflammation (Vim3B4), differentiation (RKSE60) and proliferation (TO-PRO-3 iodide) and analysed flow cytometrically. Clinically, patients improved significantly after 8 weeks of treatment. This clinical effect was preserved for the rest of the period of treatment with no further significant improvement. Proliferative activity also decreased significantly after 8 weeks of treatment. Proliferation did not show further significant decreases or habituation after 12, 18 and 24 weeks. For inflammation, no statistically reliable trends could be seen. Differentiation improved significantly after 8 weeks of treatment, but decreased again significantly after 12 weeks. In the period from 12 to 24 weeks, no further significant change was observed. We conclude that tacalcitol is an effective antipsoriatic drug. Prolonged treatment with tacalcitol will generally maintain improvement at the level reached after 8 weeks. Owing to the beneficial effect on both clinical state and proliferation, tacalcitol is likely to be an adequate maintenance therapy.

Entry into afferent lymphatics and maturation in situ of migrating murine cutaneous dendritic cells

An important property of dendritic cells (DC), which contributes crucially to their strong immunogenic function, is their capacity to migrate from sites of antigen capture to the draining lymphoid organs. Here we studied in detail the migratory pathway and the differentiation of DC during migration in a skin organ culture model and, for comparison, in the conventional contact hypersensitivity system. We report several observations on the capacity of cutaneous DC to migrate in mouse ear skin. (i) Upon application of contact allergens in vivo the density of Langerhans cells in epidermal sheets decreased, as determined by immunostaining for major histocompatibility complex class II, ADPase, F4/80, CD11b, CD32, NLDC-145/DEC-205, and the cytoskeleton protein vimentin. Evaluation was performed by computer assisted morphometry. (ii) Chemically related nonsensitizing or tolerizing compounds left the density of Langerhans cells unchanged. (iii) Immunohistochemical double-staining of dermal sheets from skin organ cultures for major histocompatibility complex class II and CD54 excluded blood vessels as a cutaneous pathway of DC migration. (iv) Electron microscopy of organ cultures revealed dermal accumulations of DC (including Birbeck granule containing Langerhans cells) within typical lymphatic vessels. (v) Populations of migrating DC in organ cultures upregulated markers of maturity (the antigen recognized by monoclonal antibody 2A1, CD86), but retained indicators of immaturity (invariant chain, residual antigen processing function). These data provide additional evidence that during both the induction of contact hypersensitivity and in skin organ culture, Langerhans cells physically leave the epidermis. Both Langerhans cells and dermal DC enter lymphatic vessels. DC mature while they migrate through the skin.

Dendritic cells in the bursal follicles and germinal centers of the chicken's caecal tonsil express vimentin but not desmin

BACKGROUND

Immunohistochemical studies with anti-vimentin and anti-desmin monoclonal antibodies were designed to determine the origin of bursal secretory dendritic cells (SDC) and follicular dendritic cells.

METHODS

The binding sites of anti-vimentin, anti-desmin, and anti-chicken-IgG specific monoclonal antibodies were visualized with a biotinylated anti-mouse-IgG, ABC Elite kit, and 4-chloronaphthol. Cells were double stained (anti-vimentin and rabbit anti-chicken-IgG Fc) to determine if the vimentin positive cells possessed surface IgG.

RESULTS

Vimentin positive cells were observed in the cortex and medulla of the bursa and germinal center and lymphoepithelial compartment of the caecal tonsil. The mesenchymal reticular cell, the basic supporting cell of the germinal center, was stained prominently by anti-vimentin and anti-desmin. Both antibodies stained the bursal cortex but only anti-vimentin bound the bursal secretory dendritic cell of the medulla. In addition to being vimentin positive and desmin negative, the bursal secretory dendritic cell possessed and the follicular dendritic cell appeared to possess IgG on their surfaces. In all the observations, B-cells were vimentin negative.

CONCLUSION

These studies suggest that follicular dendritic cells and mesenchymal reticular cells in the caecal tonsil's germinal centers may be functionally different cell populations while the bursal secretory dendritic cell and follicular dendritic cell of the caecal tonsil may have a common origin.

Differentiation of bursal secretory-dendritic cells studied with anti-vimentin monoclonal antibody

Embryonic and posthatched differentiation of bursal secretory dendritic cells, which express vimentin intermediate filaments, were studied with anti-vimentin (clone 3B4) and anti-cytokeratin (clone Lu5) monoclonal antibodies. Anti-cytokeratin staining revealed that medullary reticular epithelial cells formed a continuous network at every age, whereas the vimentin positive cells were single and showed dendritic appearance. On the basis of location, number, shape, polarized appearance, and Ia staining, the vimentin-positive cells and secretory dendritic cells appeared to be the same cell. Secretory dendritic cell precursors entered the bursal epithelium between 11 and 13 days of embryogenesis. The first vimentin positive cell appeared in the bud of 14-day embryos. Bud formation preceded the appearance of vimentin-positive cells. These observations suggested that the secretory dendritic cell precursor did not express vimentin when it entered the epithelium. Between 15 days of embryogenesis and 2 weeks of posthatch development, the changes in vimentin staining pattern revealed a cytological differentiation of the vimentin-positive cell. During rapid bursal growth, the number of secretory dendritic cells (vimentin-positive cells) increased about 18 times possibly by proliferation of vimentin-negative precursors in the epithelial arches of the corticomedullary border.

Anti-vimentin monoclonal antibody recognizes a cell with dendritic appearance in the chicken's bursa of Fabricius

The bursa of Fabricius was studied by immunohistochemical method using anti-vimentin monoclonal antibody (clone 3B4). This monoclonal antibody identified a vimentin positive cell in the medulla of the bursal follicle. During the first 2 weeks of life the vimentin positive cells located along the corticomedullary border and later became prominent in the medulla with the exception of a narrow zone adjacent to the corticomedullary border. After hatching the accumulation of vimentin-type intermediate filaments on one side of the nucleus endowed the vimentin positive cells with a polarized appearance. This "cap-like" vimentin positive area of the cytoplasm determined the position of the major cell process. Within the medulla the Ia positive secretory dendritic cells contained secretory granules in one of the cell processes. The distribution, shape, and polarized appearance of the vimentin positive cells were identical with that of the secretory dendritic cells. Therefore, the anti-vimentin monoclonal antibody proved to be useful for identification of the bursal secretory dendritic cells. During rapid bursal growth the number of secretory dendritic cells increased, possibly, by proliferation of vimentin negative secretory dendritic cell precursors located along the corticomedullary border.

Endogenous peroxidase- and vimentin-positive cells accumulate at the corticomedullary border of the chicken thymus

The granulopoietic activity of the thymus and bursa of Fabricius was analyzed using an anti-vimentin monoclonal antibody and endogenous peroxidase reaction to detect possible hemopoietic precursors and functionally mature cells, respectively. Endogenous peroxidase-positive cells (EPC) and vimentin-positive cells (V9) were located at the corticomedullary zone of the thymus. The cells were grouped, suggesting their clonal expansion. The first EPC appeared in the thymus on Day 15 of embryonic age, 2 and 3 days later than in the bursa of Fabricius and spleen, respectively. They were intermingled with thymocytes. Although the bursal EPC disappeared by Day 7 after hatching, the number of thymic EPC continued to increase. The thymic EPC and V9 cells persisted for more than 12 wk of age. The V9 cells were present either as single cells or grouped cells in the 15-day-old embryos. The V9 cells represented a distinct cell population of the corticomedullary border that may cooperate with the EPC.

Abundant dendritic cells express HLA-DR in pleomorphic adenomas

Most pleomorphic adenomas were found to contain abundant dendritic cells (DC) with major histocompatibility complex (MHC) class II (HLA-DR) expression. Their immunohistochemical staining features were suggestive of dendritic histiocytic cells. Extensive phenotypic characterization by two-colour immunofluorescence staining for various cell markers was performed. The DC expressed both HLA class I and II determinants, vimentin, S-100 protein, and various monocyte-related markers (10G11, 3D10, 7G5 or CD11a, 8C2) but were negative for leucocyte common antigen (CD45), Leu-6 (CD1), and the myelomonocytic L1 antigen. Characterization of HLA-DR positive DC isolated by an immunomagnetic bead method confirmed the immunohistochemical staining pattern that corresponds to the phenotype of interdigitating cells. Morphological and immunological implications of the abundant presence of these cells in pleomorphic adenomas are discussed.

Immunogold staining of intermediate-sized filaments of the vimentin type in human skin: a postembedding immunoelectron microscopic study

We have studied the localization of vimentin in normal human skin at the ultrastructural level using a monoclonal mouse anti-vimentin antibody and a postembedding immunogold-staining technique on thin sections of Lowicryl K4M embedded biopsies. Selective immunogold labeling of intermediate-sized filaments (IF) of epidermal Langerhans cells and melanocytes and of dermal fibroblasts was demonstrated. The IF of fibroblasts were more intensely stained than those of the epidermal dendritic cells; cell processes and dendrites of all three cell populations exhibited a greater number of IF and more pronounced immunogold-labeling than the perinuclear cytoplasm, relating IF of the vimentin type to dendrite formation and/or function. The method described is an appropriate tool for immunoelectron microscopic studies of IF of the vimentin type in situ.

Patterns of expression of trichocytic and epithelial cytokeratins in mammalian tissues. I. Human and bovine hair follicles

The cytokeratin family of intermediate filament (IF) proteins can be grouped into the epithelial polypeptides ("soft alpha-keratins"), of which at least 19 exist in the various human epithelia, and the hair-type cytokeratins ("hard alpha-keratins"), which are typical of trichocytes, i.e., the living hair-forming cells. We have recently shown [34] that the hair follicles from diverse mammalian species contain a set of eight major cytokeratin polypeptides, four each of the acidic (type I) and the basic (type II) subfamily, which are different from all known epithelial cytokeratins. In addition, we have identified two new minor trichocytic cytokeratin polypeptides, designated Hax (type I) and Hbx (type II). Antibodies against trichocytic cytokeratins that do not crossreact with any of the epithelial cytokeratins have enabled us to study the expression of both kinds of cytokeratin in the various cell types of human and bovine hair follicles. Using immunofluorescence microscopy, we have observed intense reactions of trichocytic cytokeratins only in cells contributing to the forming hairs, i.e., hair shaft, medulla and cuticle, whereas immunostaining of the peribulbar matrix cells was weaker, if at all detectable. In contrast, epithelial cytokeratins were localized in both the inner and outer root sheath epithelia but, surprisingly, also in certain portions of the trichocyte column, notably cells of the cuticle, certain medullary cells, and trichocytes of the basalmost peripapillary cell layers. Cells coexpressing trichocytic and epithelial cytokeratins have been identified by double-label immunofluorescence microscopy. Epithelial cytokeratins of the inner and outer root sheath epithelia include, most remarkably, "simple-epithelium-type" cytokeratins 8, 18, and 19; these occur in certain peribulbar regions, in distinct patterns, but with variable frequencies. The occurrence of simple epithelial cytokeratins in hair follicles has also been confirmed by high-sensitivity immunoblotting of follicular polypeptides separated by gel electrophoresis. Vimentin-positive cells were abundantly interspersed (in some follicles, but not in all) between the trichocytes of the peripapillary cone, most of them probably being melanocytes. The cell-type complexity of the hair follicle and the different patterns of cytoskeletal protein expression in the various hair follicle cells are discussed in relation to the development and growth of this organ.

Role of epidermal Langerhans cells in viral infections

Langerhans cells function as highly potent antigen-presenting cells in the epidermis. In the last few years, their role in viral infections has been studied in various experimental systems. They have been shown to be involved in the pathogenesis of a number of infections of viral origin. These include vaccinia virus, human papilloma virus, herpes simplex virus, foot and mouth disease virus and human retrovirus infections. Studies on the effect of various factors, that are known to modulate the activity and density of Langerhans cell in the epidermis, may lead in the future to the development of new strategies aimed at inhibiting virus infections or even eradicating latent infection.

A comparative immunohistochemical study of cytokeratin and vimentin expression in middle ear mucosa and cholesteatoma, and in epidermis

Cytokeratin expression was studied in human middle ear cholesteatoma lesions, using a variety of immunohistological techniques and a wide range of polyclonal antisera and monoclonal antibodies against cytokeratin (CK) subgroups or individual CK polypeptides. The expression of the other cytoskeletal proteins, vimentin and desmin, was also investigated. Middle ear mucosa and epidermal tissues were used as reference tissues. Our investigations also included epithelial structures present in the cholesteatoma perimatrix and in dermal tissues. The results indicate that, compared with epidermal tissues, the expression profile of CKs in cholesteatoma matrix is representative of a hyperproliferative disease. Evaluating the presence of a marker of terminal keratinization - the 56.5 kD acidic CK n degrees 10 - we found supportive evidence of a pronounced retardation of its expression, which did not parallel histological differentiation. In epidermal tissues, the first prickle cell layers are CK10 positive whereas in many cholesteatomas this finding was observed near the stratum granulosum only. Probing the early stages of keratinization - the 58 kD basic CK n degrees 5 and the 50 kD acidic CK n degrees 14 - we regularly observed an extended staining area in the cholesteatoma matrix. In epidermal reference tissues, only the basal and nearest suprabasal layers were convincingly labeled. As a rule, non-epidermal CKs did not belong to the cholesteatoma CK set. However, exceptions to that rule were noticed as a focal or more extended expression of one or more non-epidermal CKs in about half of the cases. Together with the extended CK5 topography, this is further evidence that CK expression is seriously affected by the diseased state. CK expression in the perimatrix is limited to mucous glands, either normal, atrophic or hyperplastic. CKs n degrees 4, 5, 7, 14, 18 and 19, also displayed by middle ear mucosa, were consistently observed. Where ductal arrangements were present, CK10 was also detected, in analogy with the CK10 registration in ductal portions of mucous glands in the external ear canal skin. The absence of CK8 in mucous glands of the perimatrix, however, strongly differentiates these structures from the mucous gland acini and ducti in the external ear canal, where CK8 is systematically expressed. Vimentin staining was restricted to dendritic cells of the matrix (Langerhans cells) and to perimatrix fibroblasts, blood cells and vascular endothelium. Coexpression of CK and vimentin was not observed.

Monoclonal antibodies for epidermal population analysis

Three keratin antibodies (RKSE 60, Clone 77, and a rabbit polyclonal) and 2 vimentin antibodies (Vim ab and a rabbit polyclonal) were investigated using frozen sections of normal and psoriatic skin. Of these, the monoclonals RKSE 60 and Vim ab were selected for quantitative population analysis of healthy epidermis, psoriatic uninvolved epidermis, and psoriatic lesions. Suspensions of isolated cells were prepared from biopsy specimens by trypsinization, and stained with RKSE 60 or Vim ab using an indirect immunofluorescence assay. Our results showed an increase in the germinative fraction from the normal value of 30% to almost 50% in the psoriatic lesion; in absolute terms this corresponds to a 6-fold increase in the size of the germinative compartment. More interesting, the germinative psoriatic uninvolved epidermis (38%) was also significantly higher than normal. The percentage of vimentin-positive cells (Langerhans cells and melanocytes) was nearly double that of normal in both the lesion and the uninvolved psoriatic epidermis. We conclude that, in contrast to statements frequently encountered in the literature, the "uninvolved" skin of the patient is morphologically and functionally different from that of the healthy individual.

Monoclonal antibodies and the skin biopsy: current and potential clinical applications

Monoclonal antibodies are becoming increasingly useful in the clinical diagnosis and/or treatment of a number of unrelated diseases. Discussion will be directed to those monoclonal antibodies recognizing antigens within the skin which appear to have either proven or potential application in the diagnostic evaluation of the skin biopsy.

Identification of Merkel cells in human skin by specific cytokeratin antibodies: changes of cell density and distribution in fetal and adult plantar epidermis

Merkel cells are special neurosecretory cells which, in adult human skin, are usually very scarce. By immunofluorescence microscopy using antibodies to human cytokeratin polypeptide no. 18, we localized distinct non-keratinocyte cells in the glandular ridges of human fetal and adult plantar epidermis. Using electron and immunofluorescence microscopy, these cells were identified as Merkel cells containing typical neurosecretory granules as well as bundles of intermediate-sized filaments and desmosomes. Two-dimensional gel electrophoresis of the cytoskeletal fractions of microdissected epidermal preparations highly enriched in Merkel cells indicated the presence of cytokeratin polypeptides nos. 8, 18 and 19 which are typical of diverse simple epithelia of the human body. Double immunofluorescence microscopy showed that these human Merkel cells contain neither neurofilaments nor vimentin filaments. In human fetuses of 18-24 weeks of age, conspicuously high concentrations of Merkel cells, reaching a density of approximately 1,700 Merkel cells/mm2 skin, were found in the glandular ridges of plantar skin. The concentration decreased considerably at newborn and adult stages. Thin cell processes (up to 20 microns long) were observed in many fetal epidermal Merkel cells. In addition, we detected isolated Merkel cells deeper in the dermis (i.e. at distances of, at most, 100 microns from the epidermis) in fetal and newborn plantar skin. Our results show that Merkel cells are true epithelial cells which, however, differ profoundly from epidermal keratinocytes in their cytokeratin expression. The findings are discussed in relation to the much disputed question of the origin of Merkel cells. The present data speak against the immigration of Merkel cells from the neural crest, but rather suggest that they originate from epithelial cells of the skin, although most probably not from differentiated keratinocytes.