Cutaneous nerves in cafe au lait spots with white halos in infants with neurofibromatosis. An electron microscopic study.

BACKGROUND AND DESIGN--Although two cardinal skin manifestations of neurofibromatosis are cutaneous neurofibromas and cafe au lait spots, the pathogenesis of cafe au lait spots are very poorly known compared with that of cutaneous neurofibromas. Thus, the cafe au lait spots in two Japanese infants were clinically, histologically, and electron-microscopically investigated. OBSERVATIONS--Some of the cafe au lait spots in the mongolian spots were surrounded by white halos. Histologically, in the cafe au lait spots, the epidermal basal cells had abundant melanin pigment, but macromelanosomes were not seen throughout the epidermis. In the white halo, the epidermal basal cells had a small amount of melanin pigment. Electron microscopically, the cafe au lait spots and their white halos had many subepidermal and intraepidermal nerves that belonged to free nerve endings. All the cutaneous nerves were mature. Some of the intraepidermal nerves had partially or completely naked axons that contacted tightly with the cytomembranes of the basal keratinocytes. Some of the axons in the subepidermal nerves showed degenerative changes only in the white halos. No ultrastructural pathologic changes were observed in the melanocytes, the epidermal keratinocytes, or melanosomes in those cells in the cafe au lait spots and their white halos; also, dermal melanocytes were absent in the both areas. CONCLUSIONS--The increase of the cutaneous nerves and the absence of dermal melanocytes in the cafe au lait spots and their white halos may be considered as characteristic histologic cutaneous findings in infants with neurofibromatosis. However, no evidence indicates that the cutaneous nerves may participate closely in the pathogenesis of the white halos.     

Epidermal changes in cutaneous lesions of sarcoidosis.

The essential histologic finding of cutaneous sarcoidosis is a noncaseating epithelioid cell granuloma in the dermis or, infrequently, in the subcutaneous tissues. However, there have been cases of cutaneous sarcoidosis with clinical appearances altered by epidermal changes such as ulcers, the formation of psoriasiform or verrucous plaques, and by hypopigmentation. In this study, histologic examinations of the epidermis were performed in cutaneous lesions of 62 cases of sarcoidosis. Seventy-nine percent (49/62) showed epidermal changes including hyperkeratosis (8/49), parakeratosis (10/49), acanthosis (6/49), and epidermal atrophy (35/49). Lymphoid cells extended into the epidermis in 50 of 62 cases. The infiltration patterns were in the forms of a spongiotic reaction (21/50), lichenoid tissue reaction (9/50), and simple exocytosis without epidermal vesiculation (20/50). Immunohistochemical studies showed that the lymphoid cells in the epidermis expressed CD3, 8, 45RO, and 11a. The epidermal changes overlying the granulomatous lesions contribute to the variety of clinical manifestations and are in part associated with the pathogenesis of cutaneous sarcoidosis.     

Iontophoresis of nickel elicits a delayed cutaneous response in sensitized individuals that is similar to an allergic patch test reaction

Wearing of patch test chambers for 1-2 days is uncomfortable for patients. Allergen application by iontophoresis avoids this, but it is unknown so far whether iontophoresis itself interferes with the delayed immune response. We compared the effects occurring 48 h after iontophoresis with distilled water, 0.9% NaCl, and 0.01 M NiSO4 in normal volunteers and in nickel-sensitized patients (total n=36). Visual assessment was performed and transepidermal water loss (TEWL), stratum corneum hydration, cutaneous blood flow, and immunohistopathology were determined. After iontophoresis with nickel sulfate, only individuals sensitized to nickel reacted with a positive clinical response, increase in cutaneous blood flow, decline in epidermal CD-1a-positive cells, increase in epidermal proliferation (Ki-67-positive cells), pronounced infiltration of cells positive for CD4, CD11, or CLA, and cellular activation (expression of ICAM1, HLA-DR). Iontophoresis with distilled water or saline did not result in such reactions in volunteers with or without nickel sensitization, and the latter also tolerated nickel iontophoresis without significant skin reactions. We conclude that the delayed cutaneous response to nickel induced via iontophoresis is specific and similar to a positive patch test reaction. Iontophoresis may therefore be considered as an alternative to patch testing.     

Epidermal stem cells

The identification of adult epidermal stem cells that are capable of self-renewal and can reconstitute not only the epidermis but also the cutaneous appendages opens new perspectives for the treatment of a variety of human skin disorders including severe burns, cutaneous cancers, alopecia and acne. However, the implementation and improvement of these novel treatment strategies require a better understanding of the biology of stem cells, in particular regarding their isolation and the maintenance of their unique characteristics in culture. In this review, we summarize the main features of epidermal stem cells and we present the most recent advances in our understanding of the development and maintenance of these cells. In addition, we discuss some of the challenges and the potential clinical applications of epidermal stem cell technology.     

Characterization of cutaneous antigen presentation in partially inbred miniature swine

Abstract MHC class I and II-defined, partially inbred miniature swine have recently become available as a large animal model in transplantation immunology. To investigate cutaneous immunocompetence in this model, cutaneous antigen presenting cell (ARC) function was assessed. For morphologic analysis, punch biopsies were examined by electron microscopy. By this technique, epidermal Langerhans cells bearing typical Birbeck granules could be detected. For functional studies, epidermal cell (EC) suspensions were prepared from split thickness skin specimens. Using FACS analysis, freshly prepared epidermal cell suspensions contained 1.8-4.7% MHC class II-positive cells. These EC potently stimulated allogeneic nylon wool-enriched peripheral blood T cells in the primary mixed EC-lymphocyte reaction. For in vivo assessment of cutaneous APC function. EC suspensions enriched for or depleted of class II-positive EC were generated by panning of class II-positive EC using mouse anti-MHC class II antibodies and anti-mouse IgG-coatcd petri dishes. EC were then coupled to the hapten trinitrophenol (TNP) and injected s.c. into autologous or MHC-mismatched pigs twice at a one week interval. One week later, pigs were challenged by s.c.-injection of 0.5-1 × 10⁷ TNP-coupled or uncoupled EC. Autologous unseparated EC as well as EC enriched for MHC class II-positive cells were able to sensitize naive animals against TNP, whereas neither TNP-coupled EC depleted of class II-positive APC, MHC-mismatched EC coupled to TNP, nor uncoupled EC induced immunity to TNP. Our data indicate that inbred miniature swine possess competent cutaneous APC which are able to induce cutaneous immunity in a manner similar to Langerhans cells in murine or human skin.     

Carbamazepine ('Tegretol') and toxic epidermal necrolysis: report of three cases with histopathological observations

Three patients who developed toxic epidermal necrolysis whilst receiving carbamazepine are described. Two patients experienced severe oropharyngeal ulceration and extensive cutaneous necrolysis with subsequent transient alopecia, nail shedding and persistent ulceration of the tongue. Histology of the skin revealed changes resembling those found in not only erythema multiforme and toxic epidermal necrolysis but also homograft rejection and the acute graft-versus-host reaction, suggesting that cutaneous damage was mediated by ‘aggressor lymphocytes’ sensitized to epidermal cells.     

Pilomatricomal horn: a new superficial variant of pilomatricoma

We describe a pilomatricomal horn on the right arm of a 39-year-old man. Although initially the tumor was clinically thought to be a verruca vulgaris, the microscopic features were similar to those found in classic pilomatricoma, except for the epidermal location and the presence of a cutaneous horn. Light microscopy showed replacement of the epidermis by basaloid cells, with masses of cornified material containing shadow cells that formed a cutaneous horn. Whereas classic pilomatricoma is confined to the deep reticular dermis or subcutis, the present case represents a unique heretofore unreported epidermal variant of pilomatricoma that pathologists should be aware of to differentiate it from malignant epidermal tumors.     

Effects of immunomodulatory cytokines on the presentation of tumor-associated antigens by epidermal Langerhans cells.

The recognition and presentation of tumor-associated antigens by cutaneous antigen-presenting cells (APC) may play an important role in the establishment of effective defense mechanisms against newly emerging tumors in the skin. Recent data demonstrate the ability of I-A+ epidermal cells (Langerhans cells) to present tumor-associated antigens for the induction of protective tumor immunity and elicitation of delayed-type hypersensitivity against the murine spindle cell tumor, S1509a. Furthermore, the local cytokine microenvironment in the vicinity of a cutaneous neoplasm may regulate the ability of resident epidermal APC to initiate and/or to elicit protective immunity against incipient cutaneous neoplasms. This article summarizes the effects of granulocyte-macrophage/colony-stimulating factor (GM-CSF), interleukin-1 alpha (IL-1 alpha), tumor necrosis factor-alpha (TNF alpha), transforming growth factor-beta (TGF beta), and interferon-gamma (IFN gamma) on the modulation of antigen presentation by epidermal APC. Our data indicate that these cytokines significantly and differentially modify the ability of epidermal cells to present tumor-associated antigens and that their effects differ with regard to induction of primary immunity (sensitization) or elicitation of secondary immune responses.     

ULTRASTRUCTURE OF CUTANEOUS LESIONS IN LUPUS ERYTHEMATOSUS: A COMPARISON BETWEEN THE CUTANEOUS AND SYSTEMIC TYPES

The author investigated the basal lamina of cutaneous lesions in lupus erythematosus (LE) at the dermal-epidermal junction ultrastructurally, and discussed the differences between cutaneous LE (CLE) and systemic LE (SLE) and also among the types of cutaneous eruptions. The findings included micro-depression of the cytoplasm of basal cells, widening of the zona lucida, dissociation between anchoring filaments and the basal lamina, separation of the lamina from epidermal cells, focal defects and bifurcations of the basal lamina, and newly formed fine basal laminae at the original sites adjacent to the basal cells. The basal lamina deeply invaded the dermis with branching or multiplication which looked like loops or labyrinths and was thickened. These changes were all considered to be antecedents to the multiplication of the basal lamina. The basal lamina was multiple and sometimes more than five-layered. The laminae of the latter are thought to be specific to LE. The distances from the outer leaflet of the plasma membranes of basal cells to the deepest points of the multilayered basal laminae in the dermis were measured. They were regarded as an index of the degree of the multiplication of the lamina. Their mean value was significantly greater in CLE than in SLE. This fact indicated that the multiplication of the basal lamina in CLE was higher than in SLE. There were no significant differences among the types of cutaneous eruptions. The basal lamina is known to be formed beneath half-desmosomes without participation of the dermis. Thus multiplication is thought to be a secondary phenomenon following repeated damage to the epidermal cells.     

T-cell subsets in drug-induced toxic epidermal necrolysis. Possible pathogenic mechanism induced by CD8-positive T cells

A patient with bromisovalum-induced toxic epidermal necrolysis showed pronounced delayed hypersensitivity to bromisovalum by patch testing. Biopsy specimens from the cutaneous lesion and the site of the positive patch test reaction were analyzed and compared immunohistologically. The findings were similar: most of the mononuclear cells disposed along the dermoepidermal junction and migrating into the epidermis were CD8-positive lymphocytes, whereas the dermal inflammatory infiltrates were composed predominantly of CD4-positive lymphocytes. This case showed the potential usefulness of patch testing in evaluating cases of toxic epidermal necrolysis. We believe that delayed hypersensitivity plays a crucial role in the development of drug-induced toxic epidermal necrolysis. Furthermore, potential effector cells with phenotypic characteristics of CD8-positive lymphocytes (suppressor/cytotoxic T cells) seem to represent important mediators of the epidermal damage of the cutaneous lesion in our case.     

Amyloidogenesis in organ-limited cutaneous amyloidosis: an antigenic identity between epidermal keratin and skin amyloid

Epidermal keratin was extracted and antibody against this protein was produced in rabbits. Various forms of organ-limited cutaneous amyloidosis (lichenoid, macular, and nodular amyloidosis, and basal cell epithelioma) and primary systemic amyloidosis were immunohistochemically examined to test the identity between epidermal keratin and skin amyloid. Amyloids in lichenoid and macular amyloidoses, and in basal cell epithelioma had an identical antigenicity with epidermal keratin, whereas amyloids in nodular amyloidosis and systemic amyloidosis did not have this identity. In addition, amyloid in lichen amyloidosis contained disulfide bonds as in keratin. Connective tissue components including filaments of fibroblasts and vascular endothelial cells did not react with this antikeratin antibody. It was concluded that at least some of the amyloid substance in organ-limited cutaneous amyloidosis is derived from degenerated epidermal keratinocytes through filamentous degeneration or apoptosis.     

Environmentally responsive and reversible regulation of epidermal barrier function by gammadelta T cells

The intraepithelial lymphocyte (IEL) network possibly composes the largest T-cell compartment in the body, but it is poorly understood. IELs show limited T-cell receptor (TCR) diversity and have been proposed to respond to generic stress signals rather than pathogen-specific antigens. Consistent with this, skin-resident TCRgammadelta+ cells, known as dendritic epidermal T cells (DETC), downregulate cutaneous inflammation, promote wound healing, and protect against cutaneous neoplasia. These pleiotropic effects collectively suggest that DETC (and IEL more generally) may contribute to epithelial maintenance and barrier function. The present studies test this hypothesis. Using skin surface impedance analysis to measure hydration status and transepidermal water loss, we show that the epidermal barrier is defective in gammadelta T-cell deficient mice. However, this does not represent a constitutive role of gammadelta cells, but rather one that is dependent on environmental challenge, consistent with the primary role for lymphocytes being the response of the host to its environment. Likewise, the importance of the physiologic DETC-associated TCR is demonstrated by showing that Vgamma5+ fetal thymocytes reconstitute the barrier function defect in TCRdelta-/- mice, while Vgamma5-/- mice also show environmentally responsive defects in cutaneous physiology.     

Epidermal keratinocytes express the adhesion molecule intercellular adhesion molecule-1 in inflammatory dermatoses

Using indirect immunofluorescence assays on frozen tissue sections of skin from healthy subjects and subjects with inflammatory skin diseases, we found that intercellular adhesion molecule-1 (ICAM-1) was expressed in a cell surface pattern on epidermal keratinocytes at the site of lymphoid infiltration in cutaneous dermatoses. ICAM-1 was not expressed on epidermal keratinocytes in noninflamed skin. Its expression was not related solely to epidermal hyperproliferation, as hyperproliferative, tape-stripped epidermis did not express ICAM-1. We have reported previously that ICAM-1 expression on epidermal keratinocytes was upregulated by treatment with interferon gamma and that activated T lymphocytes bound to cultured epidermal keratinocytes in vitro by lymphocyte function associated-1 (LFA-1) molecules on T cells and ICAM-1 on epidermal keratinocytes. Taken together, these data suggest that upregulation of expression of ICAM-1 is an important feature of cutaneous inflammation.     

Epithelial stem cells in the skin: definition, markers, localization and functions

In recent years, cutaneous epithelial stem cells have attained a genuine celebrity status. They are considered the key resource for epidermal and skin appendage regeneration, and are proposed as a preferential target of cutaneous gene therapy. Follicular epithelial stem cells may also give rise to a large variety of epithelial tumors, and cutaneous epithelial stem cells likely are crucial targets for physical or chemical agents (including carcinogens) that damage the skin and its appendages. However, as this Controversies feature illustrates, few experts can agree on how exactly to define and identify these elusive cells, or on where precisely in the skin they are localized. Given their potential importance in skin biology, pathology and future dermatological therapy, it is, therefore, timely to carefully reconsider the basic questions: What exactly is a stem cell, and how can we reliably identify epithelial stem cells? How many different kinds are there, and how do they differ functionally? Where exactly in the skin epithelium is each of the putative stem cell subpopulations located, and can we selectively manipulate any of them?     

Epidermal basaloid proliferation in cutaneous myxomas

BACKGROUND: Basaloid epidermal proliferations, which histologically resemble basal cell carcinoma, have been described overlying dermatofibromas. Several etiologies have been proposed. Cutaneous myxomas are also benign mesynchymal tumors. PURPOSE: Basaloid proliferations have been noted overlying cutaneous myxomas. We have undertaken a study to attempt to differentiate whether these are basal cell carcinomas or benign basaloid proliferations. METHODS: Thirty cases of cutaneous myxomas were included in this study. The lesions were stained with hematoxylin-eosin and alcian blue. Immunohistochemical staining for both epidermal growth factor receptor (EGF-r) and p53 protein was performed on the cutaneous myxomas with epidermal basaloid proliferation. RESULTS: Of the 30 cases of cutaneous myxomas, nine were found to have an associated overlying basaloid proliferation. The basaloid proliferations were limited to the epidermis overlying the myxoid changes within the dermis. Mitotic figures were rare. Staining for p53 protein showed scattered positive staining in the basal cells in both the basaloid proliferations and adjacent epidermis. EGF-r showed positive staining of the overlying epidermis and basaloid proliferation in five cases. CONCLUSIONS: We report basaloid proliferations overlying cutaneous myxomas and propose that these represent benign adnexal proliferations rather than superficial basal cell carcinoma and are analogous to the basaloid proliferations overlying dermatofibromas.     

Cutaneous T-cell lymphoma lesional epidermal cells activate autologous CD4+ T lymphocytes: involvement of both CD1+OKM5+ and CD1+OKM5- antigen-presenting cells

Cutaneous T-cell lymphoma is characterized by infiltration of the skin by activated CD4+ T lymphocytes. The mechanism by which these T lymphocytes achieve and maintain their activated state is unknown. Antigen-specific activation of T lymphocytes is dependent upon antigen-presenting cells which express HLA-DR class II major histocompatibility complex molecules, such as epidermal Langerhans cells. In addition to CD1+DR+ Langerhans cells, cutaneous T-cell lymphoma lesional epidermis contains major histocompatibility complex class II positive non-Langerhans cell populations, including CD1+OKM5+ bone-marrow-derived cells and DR+ keratinocytes. We asked whether any of these epidermal cell populations demonstrate capacity to activate T lymphocytes. Various numbers of epidermal cells from uninvolved and involved cutaneous T-cell lymphoma plaques were therefore used to stimulate autologous CD4+ and CD8+ T lymphocytes in the absence of exogenous antigen. Involved epidermal cells potently induced proliferation of CD4+ T lymphocytes (S.I. +/- SEM = 466 +/- 45). In contrast, uninvolved epidermal cells only induced background levels of proliferation (S.I. +/- SEM = 2 +/- 0.5, N = 8, p less than 0.01). Neither involved nor uninvolved epidermal cells were able directly to activate CD8+ lymphocytes. The capability of involved epidermal cells to activate CD4+ T lymphocytes was dependent upon CD1+DR+ leukocytes and not DR+ keratinocytes, because depletion of either HLA-DR+, CD1+ or HLe1+ epidermal cells totally abrogated the T-lymphocyte proliferation. Interestingly, on a cell per cell basis CD1+DR+ cells obtained from involved skin, demonstrated relative to CD1+DR+ cells from uninvolved skin, enhanced capacity to activate CD4+ T lymphocytes. Furthermore, CD1+OKM5+ cells from involved epidermis stimulated autologous CD4+ T lymphocytes. This indicates that a unique hitherto undescribed CD1+OKM5+ epidermal antigen-presenting cell population may participate in T-lymphocyte activation. These findings provide support for the concept that the epidermal cells in cutaneous T-cell lymphoma patients, particularly the antigen-presenting cells, may contribute significantly to the activation of CD4+ malignant and/or non-malignant inflammatory T lymphocytes within the skin.     

Immunohistochemical study of epidermal nerve fibres in involved and uninvolved psoriatic skin using confocal laser scanning microscopy

Abstract Psoriasis is a typical hyperproliferative epidermal disease whose aetiopathogenesis is still to be defined. One of the most likely hypotheses is that it has a neurogenic origin correlated with an altered release of some neuropeptides by sensitive cutaneous nerves via antidromic pathways. As there are conflicting reports about the existence of cutaneous nerve alterations in psoriasis, we carried out an immunolocalization study using the protein gene product 9.5 as a marker for neuronal structures observed by confocal laser scanning microscopy in order to determine the pattern of sensory nerves in psoriatic skin. The investigation was carried out on cutaneous biopsies taken from involved (mature and long-established lesions) and uninvolved skin of ten patients with extensive chronic plaque psoriasis. In uninvolved psoriatic skin a significant decrease in epidermal nerve fibres was found, a further decrease was observed in mature lesions and almost a complete lack of epidermal nerve fibres in long-established psoriatic lesions. The reduction in epidermal nerve fibres and the consequent loss of relationship between these nerve structures and the skin immunocompetent cells (antigen-presenting cells, Langerhans cells, keratinocytes) might be a factor of fundamental importance in the self-maintenance of the disease. Received: 26 May 1997     

Pseudoepitheliomatous hyperplasia in cutaneous T-cell lymphoma. A clinical, histopathological and immunohistochemical study with particular interest in epithelial growth factor expression. The French Study Group on Cutaneous Lymphoma

Pseudoepitheliomatous hyperplasia has occasionally been reported in cutaneous T-cell lymphoma (CTCL). This association raises the question of the relationship between epidermal hyperplasia and the lymphomatous infiltrate. Because epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) have been demonstrated to be involved in epidermal proliferation through binding to EGF receptor (EGFr), we tested the hypothesis that these cytokines could be secreted by lymphomatous cells, and induce the overlying pseudoepitheliomatous hyperplasia. The purposes of this study were: (i) to describe the clinical and immunohistological features of pseudoepitheliomatous hyperplasia; (ii) to determine its frequency in a large series of CTCLs; and (iii) to evaluate the expression of EGF, TGF-alpha and EGFr in CTCL with or without pseudoepitheliomatous hyperplasia. Eleven cases of CTCL with pseudoepitheliomatous hyperplasia were collected from a series of 353 cases of cutaneous lymphoma registered from 1990 to 1996. They consisted of eight of 28 (28.5%) CD30+ large T-cell lymphomas and three of 148 (2%) cases of mycosis fungoides. Epidermal expression of EGF, EGFr and TGF-alpha was stronger in CTCL than in control normal human skin. Lymphomatous T cells expressed EGF and TGF-alpha whereas no expression of these cytokines could be detected in cutaneous and nodal B-cell lymphomas, nor in a normal lymph node. In addition, epidermal expression of EGFr was stronger in CTCL with pseudoepitheliomatous hyperplasia than in control cases of CTCL without pseudoepitheliomatous hyperplasia, suggesting that these cytokines, in association with other factors, are probably involved in the epidermal hyperplasia observed in some cases of CTCL.     

Loss of integrin alpha9beta1 results in defects in proliferation, causing poor re-epithelialization during cutaneous wound healing

The wound microenvironment comprises constituents, such as the extracellular matrix (ECM), that regulate with temporal and spatial precision, the migratory, proliferative, and contractility of wound cells. Prompt closure of the wound is an early and critical phase of healing and beta1 integrins are important in this process. We previously reported a marked increase in integrin alpha9beta1 expression in epidermal keratinocytes in cutaneous and corneal wounds. However, the functional role of keratinocyte alpha9beta1 during re-epithelialization is unknown and analysis has been precluded by the lethal phenotype of integrin alpha9beta1 knockout mice. We now report that in conditional integrin alpha9 knockout (K14-alpha9 null) mice, normal proliferation occurs in epidermal keratinocytes and corneal basal cells. Normal epidermal keratinocyte morphology is also retained. However, corneal basal cell morphology and epithelial thickness are altered, suggesting that loss of integrin alpha9beta1 results in abnormal corneal differentiation. In cutaneous wounds, the number of proliferating epidermal keratinocytes is significantly reduced in K14-alpha9 null mice compared with alpha9(fl/-) mice, but not in Cre (control) mice. The decreased keratinocyte proliferation observed in K14-alpha9 null mice negatively impacts healing, resulting in a thinner migrating epithelium, demonstrating that alpha9beta1 is crucial for efficient and proper re-epithelialization during cutaneous wound healing.     

Normal human Merkel cells are present in epidermal cell populations isolated and cultured from glabrous and hairy skin sites

The Merkel cell is a highly specialized cell that primarily acts as a slowly adapting mechanoreceptor. Merkel cells are scarce in normal skin but can be identified by the expression of distinct keratin filaments. Merkel cells constitute a very unique population and many questions still remain as to their origin, number, proliferative capacity, and functions in cutaneous biology. The dissociation of epidermal cells from skin is a widely used technique to extract and culture keratinocytes. We took advantage of a two-step extraction method to quantify keratin-20-expressing Merkel cells among total cutaneous cells obtained from either hairy or glabrous skin biopsies. Flow cytometry analysis revealed that keratin-20-labeled Merkel cells represent between 3.6% and 5.7% of freshly dissociated basal epidermal cells. No significant differences were seen between samples derived from glabrous palmar and hairy anatomic sites, from children and adult, respectively. We also report on the presence of Merkel cells in primary and first subcultures of epidermal cells indicating their capacity to remain viable after extraction from skin of various anatomic sites. To our knowledge, this is the first demonstration of nontumorigenic human Merkel cells in culture in vitro. The persistence of a small number of Merkel cells in culture suggests that, with the development of appropriate culture conditions, these cells could be amplified and further studied to unravel long-standing questions relative to their paracrine function or epithelial origin.