The diagnostic utility of Merkel cell polyoma virus immunohistochemistry in cytology specimens

OBJECTIVE

Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine neoplasm that predominantly affects elderly and immunocompromised patients. Merkel cell polyoma virus (MCPyV) is clonally integrated into the majority of MCCs and has been linked to patient outcomes, playing a central role in the pathogenesis of the disease. We aimed to assess the utility of MCPyV immunohistochemistry (IHC) in the diagnosis of MCC in cytology cell block specimens and correlating with clinicopathologic features.

METHODS

Fifty-three cytology samples of MCC with sufficient cell block material were stained for MCPyV by IHC and scored semi-quantitatively in extent and intensity. Morphologic mimics of MCC including small cell lung carcinoma (n = 10), non-Hodgkin lymphoma (n = 10), basaloid squamous cell carcinoma (n = 6) and other neuroendocrine carcinomas (n = 8) were stained in parallel. Positive staining was defined as >1% of the tumour cells showing at least moderate staining intensity.

RESULTS

The cytologic features of MCC were characterized by high nuclear-cytoplasmic ratios, hyperchromatic nuclei with 'salt and pepper' chromatin, and nuclear moulding. MCPyV was detected in 24 of 53 cases (45%). Staining was strong and diffuse in roughly half of the positive samples. Of the morphologic mimics, one follicular lymphoma showed strong and diffuse staining. In contrast to prior studies, we saw no association between MCPyV status and patient outcomes.

CONCLUSION

Merkel cell polyoma virus IHC is highly specific (97%) for the diagnosis of MCC in our cohort, and can serve as a useful diagnostic tool for distinguishing MCC for morphologic mimics.

The Effect of Oxaliplatin on the Immunogenic Cell Death and Cell Apoptosis of Human Merkel Cell Cancerous Tumor

Oxaliplatin, as previously studied in the paper, is a derivative of Cisplatin that is effective in treating the Lewis Lung Carcinoma (LLC)4. As it can actively induce immunogenic cell death of the cancer cells, and result in apoptosis, which increases the therapeutic efficacy in the LLC cancer treatment.4 Merkel cell caner is a type of skin cancer that is rare but highly aggressive, with high metastasizing and reoccurring rate. In this study, we aim the determine the potential of Oxaliplatin to induce apoptosis and ICD in cancerous Merkel cell line MCC1, in associate with the PD-1 inhibitor Nivolumab. The cancer cells will be treated with Oxaliplatin at concentrations 1 mM, 10 mM, or 100 mM. Avelumab and PBS will be used as the positive and negative control, respectively. The treated cells will be measured by checking for tumor size change in confocal microscopy and MTT assay, measuring the ICD using flow cytometry analysis of CRT expression, and conducting Western Blot for Cytokeratin 20 expression. The results of the study will provide insights on the potential of Oxaliplatin as a treatment of Merkel Cell Cancer in the future.

Merkel Cell Hyperplasia Versus Intraepidermal Merkel Cell Carcinoma: A Comparative Study of 2 Cases

ABSTRACT

Intraepidermal Merkel cell hyperplasia and Merkel cell carcinoma represent 2 histologically similar-appearing diagnoses with significant differences regarding prognosis and management. We present 1 case of each diagnosis to highlight characteristic histopathologic and immunohistochemical features. Our case of Merkel cell hyperplasia was identified by its small intraepidermal nest of monomorphic cells without atypia or mitoses, which demonstrated cytoplasmic, rather than perinuclear dot, patterning on CK20 staining. This can be contrasted with our case of intraepidermal Merkel cell carcinoma, which, despite a lack of dermal extension, demonstrated large nests of pleomorphic cells with frequent mitoses and apoptoses. The diagnosis was further confirmed by immunohistochemistry because CK20 staining showed classic perinuclear dot patterning. By presenting both diagnoses in parallel, this comparison aims to underscore crucial histopathologic and immunohistochemical similarities and differences.

Merkel Cell Carcinosarcoma With a Bland Sarcomatous Component

ABSTRACT

Merkel cell carcinoma with a sarcomatous component is very rare, with only 12 cases reported in the literature, often with overtly malignant myoid differentiation. We report a case of metastatic Merkel cell carcinosarcoma presenting in a lymph node 6 months after a diagnosis of cutaneous Merkel cell carcinoma with conventional histologic features. The metastatic lesion showed a unique biphasic appearance with admixed populations of neuroendocrine epithelial cells and fascicles of mitotically active spindle cells with mild cytological atypia. In addition to the immunomorphological features, a common molecular profile between the epithelial and mesenchymal components further supported the notion of carcinosarcoma in this case. To the best of our knowledge, a bland sarcomatous component has not been previously described in Merkel cell carcinosarcoma, which can be easily overlooked as a reactive stromal reaction microscopically.

Merkel cell polyomavirus large T antigen binding to pRb promotes skin hyperplasia and tumor development

Clear evidence supports a causal link between Merkel cell polyomavirus (MCPyV) and the highly aggressive human skin cancer called Merkel cell carcinoma (MCC). Integration of viral DNA into the human genome facilitates continued expression of the MCPyV small tumor (ST) and large tumor (LT) antigens in virus-positive MCCs. In MCC tumors, MCPyV LT is truncated in a manner that renders the virus unable to replicate yet preserves the LXCXE motif that facilitates its binding to and inactivation of the retinoblastoma tumor suppressor protein (pRb). We previously developed a MCPyV transgenic mouse model in which MCC tumor-derived ST and truncated LT expression were targeted to the stratified epithelium of the skin, causing epithelial hyperplasia, increased proliferation, and spontaneous tumorigenesis. We sought to determine if any of these phenotypes required the association between the truncated MCPyV LT and pRb. Mice were generated in which K14-driven MCPyV ST/LT were expressed in the context of a homozygous RbΔLXCXE knock-in allele that attenuates LT-pRb interactions through LT's LXCXE motif. We found that many of the phenotypes including tumorigenesis that develop in the K14-driven MCPyV transgenic mice were dependent upon LT's LXCXE-dependent interaction with pRb. These findings highlight the importance of the MCPyV LT-pRb interaction in an in vivo model for MCPyV-induced tumorigenesis.

Quantitative and qualitative normative dataset for intraepidermal nerve fibers using skin biopsy

BACKGROUND

Skin biopsy is the most relevant tool to diagnose small-fiber neuropathy. A well-documented normal dataset for intraepidermal nerve fiber in the distal leg is required to improve its diagnostic value.

METHODS

Three hundred healthy subjects were enrolled in the study, after clinical and biological screening to exclude neurological and systemic pathologies. A distal leg biopsy was taken and intraepidermal nerve fiber density after protein gene product-9.5 immunocytochemistry with brightfield microscopy was determined. Morphological variations of intraepidermal nerve fibers, previously described in small-fiber neuropathies, were analyzed. One hundred biopsies were also analyzed at the ultrastructural level.

FINDINGS

The median number of fibers was lower in men compared to women and decreased with age. Using statistical modeling taking into account age and gender, we calculated the 5th percentile of intraepidermal nerve fiber density as follows: 7.6156-0.0769 x age (years) + 1.5506 x gender (woman = 1; man = 0). We observed a low frequency of large swellings or horizontal branchings but an increasing frequency of small swellings of intraepidermal nerve fibers and irregular distribution along the dermal-epidermal junction with age. Axonal diameter of unmyelinated fibers of the papillary dermis did not vary with age or gender. Ultrastructural analysis also showed that fiber endings in close apposition to Merkel cells should not be mistaken for small-fiber swellings.

CONCLUSIONS

Our dataset allows accurate calculation of the normal density of intraepidermal nerve fibers for each year of age and provides original morphological observations that improve the diagnostic value of skin biopsy in the distal leg for small-fiber neuropathy.

Intact subepidermal nerve fibers mediate mechanical hypersensitivity via the activation of protein kinase C gamma in spared nerve injury

BACKGROUND

Spared nerve injury is an important neuropathic pain model for investigating the role of intact primary afferents in the skin on pain hypersensitivity. However, potential cellular mechanisms remain poorly understood. In phosphoinositide-3 kinase pathway, pyruvate dehydrogenase kinase 1 (PDK1) participates in the regulation of neuronal plasticity for central sensitization. The downstream cascades of PDK1 include: (1) protein kinase C gamma (PKCg) controls the trafficking and phosphorylation of ionotropic glutamate receptor; (2) protein kinase B (Akt)/the mammalian target of rapamycin (mTOR) signaling is responsible for local protein synthesis. Under these statements, we therefore hypothesized that an increase of PKCg activation and mTOR-dependent PKCg synthesis in intact primary afferents after SNI might contribute to pain hypersensitivity.

RESULTS

The variants of spared nerve injury were performed in Sprague-Dawley rats by transecting any two of the three branches of the sciatic nerve, leaving only one branch intact. Following SNIt (spared tibial branch), mechanical hyperalgesia and mechanical allodynia, but not thermal hyperalgesia, were significantly induced. In the first footpad, normal epidermal innervations were verified by the protein gene product 9.5 (PGP9.5)- and growth-associated protein 43 (GAP43)-immunoreactive (IR) intraepidermal nerve fibers (IENFs) densities. Furthermore, the rapid increases of phospho-PKCg- and phosphomTOR-IR subepidermal nerve fibers (SENFs) areas were distinct gathered from the results of PGP9.5-, GAP43-, and neurofilament 200 (NF200)-IR SENFs areas. The efficacy of PKC inhibitor (GF 109203X) or mTOR complex 1 inhibitor (rapamycin) for attenuating mechanical hyperalgesia and mechanical allodynia by intraplantar injection was dose-dependent.

CONCLUSIONS

From results obtained in this study, we strongly recommend that the intact SENFs persistently increase PKCg activation and mTOR-dependent PKCg synthesis participate in the initiation and maintenance of mechanical hypersensitivity in spared nerve injury, which represents as a novel insight into the therapeutic strategy of pain in the periphery.

Merkel Cell Polyomavirus Small T Antigen Induces Cancer and Embryonic Merkel Cell Proliferation in a Transgenic Mouse Model

Merkel cell polyomavirus (MCV) causes the majority of human Merkel cell carcinomas (MCC) and encodes a small T (sT) antigen that transforms immortalized rodent fibroblasts in vitro. To develop a mouse model for MCV sT-induced carcinogenesis, we generated transgenic mice with a flox-stop-flox MCV sT sequence homologously recombined at the ROSA locus (ROSAsT), allowing Cre-mediated, conditional MCV sT expression. Standard tamoxifen (TMX) administration to adult UbcCreERT2; ROSAsT mice, in which Cre is ubiquitously expressed, resulted in MCV sT expression in multiple organs that was uniformly lethal within 5 days. Conversely, most adult UbcCreERT2; ROSAsT mice survived low-dose tamoxifen administration but developed ear lobe dermal hyperkeratosis and hypergranulosis. Simultaneous MCV sT expression and conditional homozygous p53 deletion generated multi-focal, poorly-differentiated, highly anaplastic tumors in the spleens and livers of mice after 60 days of TMX treatment. Mouse embryonic fibroblasts from these mice induced to express MCV sT exhibited anchorage-independent cell growth. To examine Merkel cell pathology, MCV sT expression was also induced during mid-embryogenesis in Merkel cells of Atoh1CreERT2/+; ROSAsT mice, which lead to significantly increased Merkel cell numbers in touch domes at late embryonic ages that normalized postnatally. Tamoxifen administration to adult Atoh1CreERT2/+; ROSAsT and Atoh1CreERT2/+; ROSAsT; p53flox/flox mice had no effects on Merkel cell numbers and did not induce tumor formation. Taken together, these results show that MCV sT stimulates progenitor Merkel cell proliferation in embryonic mice and is a bona fide viral oncoprotein that induces full cancer cell transformation in the p53-null setting.

Merkel cell-poor trichoblastoma with basal cell carcinoma-like foci

We reexamined 11 cases of trichoblastoma, and two cases of trichoblastoma with basal cell carcinoma (BCC)-like foci were found. In these two trichoblastomas with BCC-like foci, the BCC-like foci were often localized in peripheral or deep areas of lesions extending out of the fibrocytic stroma. Immunohistochemistry was performed in five conventional trichoblastomas and in two trichoblastomas with BCC-like foci, using antibodies against CK20 and CK15. No CK20-positive Merkel cells and no expression of CK15 were seen in any neoplastic aggregations of the two trichoblastomas with BCC-like foci. In contrast, increased numbers of Merkel cells and positive staining for CK15 were observed in all five trichoblastomas without BCC-like foci. The five trichoblastomas without BCC-like foci included two trichoblastomas with a popped out or shelled out appearance, which characteristically had a thick fibrous capsule surrounding the fibrotic stroma, demonstrating numerous Merkel cells in the aggregations. Some trichoblastomas may undergo mutations, resulting in the development of foci of BCC and in the loss of the expression of CK15 as well as the disappearance of Merkel cells.

Merkel Cell Tumor in a Trichilemmal Cyst: Collision or Association?

An 86-year-old white male presented with an erythematous, painless, slowly growing, and firm left thigh nodule. Histologic examination revealed a dermal proliferation of monomorphous cells arranged in trabeculae, nests, and sheets with an infiltrative growth pattern. The cells had a high nuclear-cytoplasmic ratio, finely granular nuclear chromatin, and nuclear molding. Numerous mitotic figures, apoptotic cells, and individual cell necrosis were present; lymphovascular invasion was identified. The tumor was attached, demonstrating pagetoid intraepithelial migration, to a follicular cyst lined by squamous epithelium, lacking a granular cell layer and filled with compact keratinous content, diagnostic of trichilemmal cyst. Immunohistochemical study revealed that tumor cells expressed pan-cytokeratin (CK), chromogranin, synaptophysin, neuron-specific enolase, and CK20 (dotlike staining pattern), thus supporting the diagnosis of Merkel cell carcinoma. The association of Merkel cell carcinoma with a cyst is an exceptionally rare occurrence. As a result of the prominent involvement of the cyst wall by tumor cells, we favor that in this case carcinoma arose in the trichilemmal cyst rather than being a collision tumor. This hypothesis is also supported by the recent observation that Merkel cells are frequently present within normal hair follicles, especially in the isthmic portion that corresponds with the area of origin of the trichilemmal cyst.

Expression of Androgen Receptor by Fibroepithelioma of Pinkus: Evidence Supporting Classification as a Basal Cell Carcinoma Variant?

The classification of fibroepithelioma of Pinkus as basal cell carcinoma or trichoblastoma remains controversial. Immunohistochemical stains for androgen receptor may be useful in differentiating basal cell carcinoma from trichoepithelioma or trichoblastoma. We studied androgen receptor expression in 13 fibroepitheliomas of Pinkus, 11 basal cell carcinomas, 12 trichoepitheliomas, and 3 trichoblastomas. Androgen receptor expression was present in 77% (10/13) of fibroepitheliomas of Pinkus, 73% (8/11) of basal cell carcinomas, 17% (2/12) of trichoepitheliomas, and 0% (0/3) of trichoblastomas. Androgen receptor expression was significantly higher in fibroepitheliomas of Pinkus compared with trichoepitheliomas and trichoblastomas (P = .0007), but not basal cell carcinoma (P = 1.00). Tumor-associated Merkel cells, a feature of benign follicular tumors, was identified by cytokeratin 20 stains. Merkel cells were identified in 85% (11/13) of fibroepitheliomas of Pinkus, 27% (3/11) of basal cell carcinoma cases, and 73% (11/15) of benign follicular tumors. Cytokeratin 20 expression was significantly higher in fibroepithelioma of Pinkus and benign follicular tumors compared with basal cell carcinomas (P = 0.0111 and P = 0.025, respectively). No significant difference was found between fibroepitheliomas of Pinkus and trichoepitheliomas and trichoblastomas (P = 1.00). Similar to basal cell carcinomas, fibroepitheliomas of Pinkus express androgen receptors, potentially supporting classification as a basal cell carcinoma. Conversely, fibroepithelioma of Pinkus demonstrates retention of Merkel cells, a feature of benign follicular tumors. Immunophenotypic evidence for the classification of fibroepithelioma of Pinkus remains inconclusive. In small, partial biopsy specimens, coexpression of androgen receptor and cytokeratin 20 may aid in the diagnosis of fibroepithelioma of Pinkus.

Response of Merkel cells in the palatal rugae to the continuous mechanical stimulation by palatal plate

The aim of the present study was to investigate the responses of Merkel cells that are numerous in the palatine rugae, due to the continuous mechanical stimulation exerted by the palatal plate. Forty golden hamsters were used in this experiment. The palatal plate was made of adhesive resin and it was set on the palate of the animal. To exert a continuous pressure, a 0.8 mm elevation on the internal surface of the palatal plate was created at the middle portion of the fourth palatine ruga. Thereafter, the number of Merkel cells in the mucosa was calculated by immunohistochemical observation. Morphological changes of Merkel cells were examined by electron microscopy. There was significant difference among the control and any of the treated groups on the number of CK20 positive Merkel cells (p < 0.05) and that numbers were decreased at the sites where continuous mechanical stimulation was exerted. Degeneration of the cytoplasm mitochondria and nerve endings, and a decrease in both the number of neurosecretory granules and cytoplasmic processes were observed. Furthermore, the presence of nuclear chromatin aggregation and fragmentation was recognized. The continuous mechanical stimulation by the palatal plate affected the responses of Merkel cells and nerve endings, thus inducing a decrease in the number of Merkel cells. A portion of these changes was also associated with the expression of apoptosis.

Merkel cells in the oral mucosa

Ninety-eight consecutive surgical biopsies of oral mucosa from 96 patients were evaluated immunohistochemically with an anti-cytokeratin 20 (CK 20) anti-body to evidence Merkel cells (MC). Fifteen cases, showing the highest number of MC, were additionally studied with chromogranin A, S-100 protein, neuro filaments, epithelial membrane antigen, and double immunostaining for CK 20 and Ki67 antibodies to evaluate MC proliferation. Electron microscopy was performed in 2 cases. MC were observed in 58 cases. The highest number of MC was found in the gingival, buccal, and palate mucosa, especially in chronically damaged oral mucosa (lichen and chronic aspecific inflammation) as well as in the mucosa overlying tumors rather than in normal or acute inflammation. MC were not observed in dysplastic or neoplastic epithelium. MC showed evidence of proliferation, as demonstrated by Ki67 positivity, in 3 cases. In conclusion, MC appear to play a role in the reparative processes of oral mucosa.

Fibroepithelioma of pinkus

An 88-year-old woman presented with an 8-year history of a slowly enlarging growth on the suprapubic area. A shave excision of this lesion demonstrated fibroepithelioma of Pinkus (FEP). Fibroepithelioma of Pinkus is an indolent growing tumor that traditionally has been classified as a variant of the basal cell carcinoma. More recent evidence favors the classification of FEP as a variant of trichoblastoma. In this case report, we identified a large FEP with benign histologic features suggestive of a follicular origin as demonstrated in part by CK 20 staining and the presence of scattered Merkel cells within the tumor. The pathogenesis of FEP remains enigmatic, and the genetic basis has yet to be fully elucidated. Complete surgical resection is considered curative.

Expression of human beta-defensin-3 in gingival epithelia

OBJECTIVE

This study aimed to investigate the expression patterns of the newly discovered human beta-defensin-3 (hBD-3) in human gingiva.

BACKGROUND

Human beta-defensins (hBDs) are a group of small, broad-spectrum, cationic antimicrobial peptides. Our recent study showed that the expression levels of hBD-1 and 2 peptides were associated with periodontal conditions.

METHODS

A total of 49 gingival biopsies were collected, including 33 samples from 21 patients with chronic periodontitis and 16 samples from 16 periodontally healthy subjects. The expression of hBD-3 was detected by immunohistochemistry and in situ hybridization. Double staining was undertaken to identify hBD-3 peptide-positive cells, using CD-1a and cytokeratin 20 as markers for Langerhans cells and Merkel cells, respectively.

RESULTS

hBD-3 peptide was detected in 88% of the samples, which was confined to the gingival epithelia. In healthy control subjects, hBD-3 peptide was more frequently detected in the basal layer as compared to the patients (53% vs. 18%, p < 0.05). In patients, hBD-3 expression extended from the basal layer to the spinous layers (82%), in which hBD-3 was confined to the basal and deep spinous layers in clinically healthy tissues from patients, whereas it extended to the superficial spinous layers in pocket tissues from patients (0% vs. 50%, p < 0.05). In both groups, hBD-3 peptide was expressed not only in gingival keratinocytes, but also in Langerhans cells and Merkel cells. hBD-3 transcripts were detected in 90% of the samples and they were confined to the basal and/or suprabasal layers of gingival epithelia.

CONCLUSIONS

This study shows that hBD-3 is frequently expressed in gingival epithelia. The appropriate expression of hBD-3 peptide may contribute to the maintenance of periodontal homeostasis, possibly through its antimicrobial effect and promotion of adaptive immune responses.

Anti-cytokeratin 20 staining of Merkel cells helps differentiate basaloid proliferations overlying dermatofibromas from basal cell carcinoma

BACKGROUND

Basaloid epidermal proliferations (BEP), morphologically resembling basal cell carcinoma (BCC), have been described overlying dermatofibromas. Distinguishing the two is important because of non-aggressiveness of BEP and local aggressiveness of BCC. The aim of this study is to determine whether CK20 antibody staining for Merkel cells can be used as an adjunct method to differentiate BEP from BCC.

METHODS

Ten cases of BEP overlying dermatofibromas were selected. Ten cases of BCC were used as control. The two groups were stained with CK20 antibody. Numerical density of CK20 stained Merkel cells in peri-lesional epidermis, BEP and BCC was determined by examining 300 cells at 400X in two separate areas by three independent pathologists. To determine statistical significance, the results were compared using t-test method.

RESULTS

Density of Merkel cells in peri-lesional epidermis was 0.2-0.3%. No merkel cells were detected in the BCC. BEP overlying dermatofibromas showed an obvious increase in CK 20 stained Merkel cells. The difference was statistically significant (P < 0.02) CONCLUSIONS: We report a significant increase in CK20 stained Merkel cells in BEP overlying dermatofibromas as compared to BCC. CK20 antibody staining for Merkel cells can be used as an adjunct method to differentiate BEP overlying dermatofibromas from BCC. Mahmoodi M, Asad H, Salim S, Kantor G, Minimo C. Anti-CK20 staining of Merkel cells helps differentiate basaloid proliferations overlying dermatofibromas from basal cell carcinoma.

Sensory abnormalities in unaffected relatives in familial adult-onset dystonia

Somatosensory abnormalities are found in adult-onset primary torsion dystonia (PTD). Therefore we assessed spatial discrimination thresholds (SDT), a measure of spatial acuity, in four multiplex families with adult-onset PTD. In family members aged 20 to 45 years vs controls (mean + 2.5 SD), abnormal SDTs were found in four of five affected with adult-onset PTD and in 12 of 49 unaffected relatives. Sensory abnormalities may be an endophenotype, possibly expressed later as adult-onset PTD.

Cytokeratin 20 confirms merkel cell metastasis to stomach

Merkel cell carcinoma (MCC) is an uncommon, aggressive neuroendocrine carcinoma of the skin. Its prognosis is poor because of involvement of regional lymph nodes and metastases to distant sites such as bone, liver, lung, and brain. Very few metastases are reported to the gastrointestinal tract. Several studies have shown the utility of cytokeratin 20 to differentiate MCC from other small round blue cell tumors, particularly those with neuroendocrine differentiation. In this case report, we present an unusual metastasis to the stomach and the utility of cytokeratin 20 immunohistochemistry to confirm MCC.

Chondroid Syringoma

Context.—Chondroid syringoma (CS) is a benign cutaneous adnexal tumor with epithelial and stromal components. Epithelial components derived from folliculo-sebaceous-apocrine germ are evident in apocrine but not in eccrine CS.

Objectives.—To further characterize pilosebaceous differentiation and to identify the presence of Merkel cells in the areas of follicular differentiation.

Design.—Histologic type, folliculo-sebaceous differentiation, character of stroma, and presence or absence of Merkel cells by cytokeratin (CK) 20 immunoreactivity were evaluated in 25 CSs (22 apocrine and 3 eccrine) from the surgical pathology files of Henry Ford Hospital (Detroit, Mich).

Results.—Most CSs occurred in the head and neck region of patients aged 40 years or older. We found no significant difference in sex, age, or location between apocrine and eccrine types. The stroma varied from myxoid (100%) to chondroid (59%), with various amounts of fat (59%) and ossification identified in 2 cases (9%) of apocrine type, but was homogeneously myxoid in the eccrine type. Follicular and sebaceous differentiation was found in 64% and 32% of apocrine CSs, respectively. Only 2 (14%) apocrine CSs with follicular differentiation were positive for CK20 (a few scattered cells in one case and numerous grouped cells in the other in association with follicular epithelium). No correlation was found between type of stroma and the presence of Merkel cells. Scattered Merkel cells were identified in 83% of normal hair follicles and in 33.3% of normal epidermis.

Conclusion.—A high proportion of apocrine CSs show folliculo-sebaceous differentiation. The presence of Merkel cells in foci of follicular differentiation of CS supports the hypothesis that Merkel cells may be an integral constituent of follicles. To our knowledge, the presence of Merkel cells in CS, particularly in proliferative form, has not been described previously in the literature.

Effects of electromagnetic radiation from a cellular telephone on epidermal Merkel cells

The number of reports on the effects induced by electromagnetic radiation (EMR) from cellular telephones in various cellular systems is still increasing. Until now, no satisfactory mechanism has been proposed to explain the biological effects of this radiation except a role suggested for mast cells. Merkel cells may also play a role in the mechanisms of biological effects of EMR. This study was undertaken to investigate the influence of EMR from a cellular telephone (900 MHz) on Merkel cells in rats. A group of rats was exposed to a cellular telephone in speech position for 30 min. Another group of rats was sham-exposed under the same environmental conditions for 30 min. Exposure led to significantly higher exocytotic activity in Merkel cells compared with the sham exposure group. This finding may indicate the possible role of Merkel cells in the pathophysiology of the effects of EMR.

The number and distribution of Merkel cells in rudimentary polydactyly

BACKGROUND

Rudimentary polydactyly histologically reveals a marked neural proliferation in the dermis and a large number of Meissner corpuscles in the dermal papillae.

OBJECTIVE

Our study was performed to determine whether this neural proliferation is related to Merkel cells.

METHOD

Using an antibody to cytokeratin 20, we examined the number and distribution of Merkel cells in 5 cases of rudimentary polydactyly, including an immature case without Meissner corpuscles.

RESULTS

Only the case without Meissner corpuscles had a markedly large number of Merkel cells and some dermal Merkel cells.

CONCLUSION

The normal number of Merkel cells in the mature cases suggests that abundant Merkel cells may appear at first and disappear after the development of neural proliferation. Merkel cells may be associated with the generation of cutaneous nerve plexus and nerve endings in the upper dermis, and possibly with the development of Meissner corpuscles, at the early stage of rudimentary polydactyly.

Merkel cells and sclerosing epithelial neoplasms

Merkel cells are normal constituents of the basal layer of the epidermis and the follicular epithelium. They have been identified in benign neoplasms with follicular germinative differentiation but seem to be absent in basal cell carcinomas (BCCs). Because sclerosing epithelial neoplasms are often sampled by small biopsies, any method that enables distinction among them would be welcome. We used immunohistochemical staining for cytokeratin 20 to assess the presence of Merkel cells in 14 cases of desmoplastic trichoepithelioma (DTE), 12 specimens of syringoma, 11 samples of morpheiform BCC, and 8 specimens of microcystic adnexal carcinoma (MAC). Merkel cells were found in association with all 14 specimens of DTE and in 1 of 11 cases of morpheiform BCC (p < 0.005) but in none of the specimens of syringoma or MAC. Our study supports previous findings that Merkel cells are seen in association with cutaneous neoplasms that are benign and of a follicular germinative origin. Although MAC may differentiate along follicular-sebaceous-apocrine lines, the absence of Merkel cells within it is consistent with its malignancy. The identification of Merkel cells in a sclerosing epithelial neoplasm of the skin points to DTE as the most likely diagnosis.

Postnatal loss of Merkel cells, but not of slowly adapting mechanoreceptors in mice lacking the neurotrophin receptor p75

Merkel cells are specialized epidermal cells which are abundantly found in touch-sensitive areas and which are innervated by slowly adapting mechanosensitive afferent fibres with large myelinated (Abeta) axons. The role of Merkel cells in mechanosensation, their developmental regulation and their influence on sensory neuron function are, however, incompletely understood. Here, we used mice lacking the neurotrophin receptor p75 which is expressed on Merkel cells to investigate their postnatal development and that of their innervating sensory neurons. Using morphological studies we now show that Merkel cells develop normally in both hairy and glabrous skin in these animals until 2 weeks old, but are progressively lost thereafter and have almost completely disappeared 2 months after birth. Using standard extracellular electrophysiological recording techniques we find that despite the profound loss of Merkel cells there is no corresponding reduction in the number of myelinated slowly adapting afferent fibres. Moreover, the mean mechanical threshold of these neurons and their average stimulus response function to suprathreshold mechanical stimuli does not change during the time period when more than 99% of Merkel cells are lost. We conclude that Merkel cells require p75 during the late postnatal development. However, neither the survival nor the mechanical sensitivity of slowly adapting mechanoreceptive Abeta-fibres depends on the presence of Merkel cells.

Loss of distal axons and sensory Merkel cells and features indicative of muscle denervation in hindlimbs of P0-deficient mice

Mice lacking the major Schwann cell myelin component P0 show a severe dysmyelination with pathological features reminiscent of the Déjérine-Sottas syndrome in humans. Previous morphological and electrophysiological studies on these mice did not only demonstrate a compromised myelination and myelin maintenance, but were suggestive of an impairment of axons as well. Here, we studied the axonal pathology in P0-deficient mice by quantitative electron microscopy. In addition, we investigated epidermal receptor end organs by immunocytochemistry and muscle pathology by histochemistry. In proximal sections of facial and femoral nerves, axon calibers were significantly reduced, whereas the number of myelin-competent axons was not diminished in 5- and 17-month-old P0-deficient mice. However, in distal branches of the femoral and sciatic nerve (digital nerves innervating the skin of the first toe) the numbers of myelin-competent axons were reduced by 70% in 6-month-old P0-deficient mice. Immunolabeling of foot pads revealed a corresponding loss of Merkel cells by 75%, suggesting that survival of these cells is dependent on the presence or maintenance of their innervating myelinated axons. In addition, quadriceps and gastrocnemius muscles showed pathological features indicative of denervation and axonal sprouting. These findings demonstrate that loss of an important myelin component can initiate degenerative mechanisms not only in the Schwann cell but also in the distal portions of myelinated axons, leading to the degeneration of specialized receptor end organs and impairment of muscle innervation.

Immunohistochemical comparison of cutaneous lymphadenoma, trichoblastoma, and basal cell carcinoma: support for classification of lymphadenoma as a variant of trichoblastoma

Cutaneous lymphadenoma is an uncommon basaloid epithelial tumor of uncertain histogenesis, most recently classified as a variant of trichoblastoma. Because characteristic immunohistochemical findings have been reported in trichoblastomas, we evaluated the staining patterns of five cutaneous lymphadenomas and compared the results to those of ten trichoblastomas and ten nodular basal cell carcinomas (BCCs), using antibodies to cytokeratin 20 (CK20), bcl-2, and CD34. In addition, because lymphadenomas contain intraepithelial S100-positive putative Langerhans cells, we compared staining of all tumor groups for S100 protein and CD1a. We also attempted to corroborate recent reports of CD30-positive activated lymphocytes in lymphadenomas. We identified CK20-positive Merkel cells in 3/5 lymphadenomas, 7/10 trichoblastomas, and none of the BCCs. Staining for bcl-2 accentuated the peripheral epithelial layer in all lymphadenomas and in 3/10 trichoblastomas, while the remaining trichoblastomas and all BCCs stained diffusely. There was stromal staining with CD34 in two lymphadenoma, 4 trichoblastomas, and 3 BCCs. All lymphadenomas featured numerous intraepithelial S100-positive cells which were also positive for CD1a in three cases tested. In addition, 8/10 trichoblastomas and 2/10 BCCs contained modest numbers of cells labelling for S100 and CD1a. Two of three lymphadenomas contained rare single cells resembling histiocytes faintly positive for CD30, and similar cells labelled for CD68. We conclude that the similar staining patterns of lymphadenomas and trichoblastomas support the classification of lymphadenoma as a variant of trichoblastoma. Staining with CD34 does not reliably distinguish between these tumors and BCCs. Lymphadenomas, trichoblastomas, and BCCs may all contain Langerhans' cells. The relationship between these cells and the striking lymphoid infiltrates seen in lymphadenomas is not clear. In our cases, the CD30-positive cells in lymphadenomas appear to represent histiocytes rather than activated lymphocytes.

Immunohistochemical investigation of the different developmental stages of trichofolliculoma with special reference to the Merkel cell

The morphologic features of trichofolliculoma are variable, reminiscent of the anagen, catagen, and telogen phases of a normal hair follicle in its cycle. We recently described an early, fully developed stage and late stages of trichofolliculoma. Using immunohistochemical examination, we sought to demonstrate hyperplasia of Merkel cells in all three stages of trichofolliculoma. We found this to be the most striking in small lesions of the late stage. The distribution of the Merkel cells in several stages of trichofolliculoma coincided with the known arrangement of normal follicular Merkel cells during the follicular cycle. However, antibodies against neurofilaments failed to detect innervated Merkel cells, in contrast to normal follicular Merkel cells. Antibodies against Ki67 did not reveal proliferative Merkel cells in any of the trichofolliculomas, but for unknown reasons, a distinct cytoplasmic staining of Merkel cell processes sometimes occurred. Nuclear Ki67 was strongly expressed in the nuclei of follicular keratinocytes of the fully developed trichofollicullomas, whereas those at a late stage showed a markedly decreased staining pattern. Our finding of Merkel cells in all trichofolliculomas underlines their classification as hamartomas with follicular differentiation. Hyperplasia of Merkel cells, even in trichofolliculomas at a late stage, as regressing lesions might implicate hitherto unknown regulatory functions of this neuroendocrine cell.

Intraepidermal cytokeratin 7 expression is not restricted to Paget cells but is also seen in Toker cells and Merkel cells

Histologically, extramammary Paget's disease and mammary Paget's disease (MPD) are characterized by large atypical cells distributed throughout the epidermis. Although classic examples of these disorders are easily diagnosed on morphologic grounds, some cases may cause differential diagnostic problems. Immunohistology with a wide variety of antibodies has been used as an aid for the identification of Paget cells, for their distinction from other entities, and for investigation of the origin or nature of the disorder. Recently, cytokeratin 7 has been proposed as a specific and 100% sensitive marker for Paget's disease. We studied 22 cases of mammary Paget's disease and 22 cases of extramammary Paget's disease with and without an underlying malignancy for their reactivity with monoclonal antibodies to cytokeratin 7 (CK7) and cytokeratin 20 (CK20). Our studies show that anti-CK7 is an effective but not 100% sensitive marker for Paget cells, staining 21 of 22 cases of mammary Paget's disease and 19 of 22 cases of extramammary Paget's disease, whereas CK20 stained 0 of 17 cases of mammary Paget's disease and 6 of 19 cases of extramammary Paget's disease. We also demonstrate that CK7, but not CK20, highlights intraepidermal clear cells with bland nuclear features (Toker cells) that have been reported in 11% of normal nipples. By using CK7 as a marker, however, we were able to identify Toker cells in most of the nipples we studied: 8 of 15 nipples from mastectomy patients without Paget's disease, and 15 of 18 autopsy cases (both male and female) with normal breasts and nipples. It also permitted us to perform more extensive phenotyping on them, showing that Toker cells share similar antigens with Paget cells and with cells lining the underlying normal lactiferous ducts. In 7 of 15 cases containing CK20-positive Merkel cells, CK7 was also seen to stain Merkel cells. In infrequent cases, Toker cells or Merkel cells may be so numerous focally that a CK7 stain may raise the possibility of involvement of the nipple by Paget's disease. An awareness of the CK7 reactivity of Toker cells and Merkel cells as well as attention to the cytologic features of the case should avoid this problem.

Merkel cell differentiation in trichoblastoma

Four cases of trichoblastoma rich in Merkel cells (MCs) are reported. They occurred in two men and two women, with ages ranging from 58 to 76 years (mean 67.5 years). MCs were detected immunohistochemically with antibodies to keratin 20, chromogranin A and neuron-specific enolase (NSE). In an attempt at better definition of the nature and role of MCs in trichoblastoma, the distribution of MCs in normal adult and fetal skins obtained at autopsy was studied. In addition, ten cases of sebaceous naevus of Jadassohn (NSJ) were evaluated along similar lines. MCs made up 2-20% of the tumour cells in trichoblastomas; they were present in normal fetal skin and were rare in normal adult skin. All but one of the cases of NSJ showed numerous positive cells in the epidermal component of the lesion with all three antibodies. Six basal cell carcinomas and one syringocystadenoma papilliferum associated with NSJ were negative with keratin 20, chromogranin A and NSE antibodies, whereas a minute trichoblastoma arising against the same background was positive for these markers. Hair follicle cell tumours may recapitulate the skin embryogenesis, as numerous MCs are present in fetal follicles, but only occasional such cells are seen in adult skin.

Immunohistochemical characterization of HSP, alpha-MSH, Merkel cells and neuronal markers in acute UV dermatitis and acute contact dermatitis in vivo

OBJECTIVE

To study the immunoneurocrine network in inflammatory dermatoses, we investigated histochemically acute UV and acute contact dermatitis.

METHODS

Antibodies were applied to frozen and paraffin specimens of human skin after irradiation (n = 10), to positive patch tests (n = 10) and controls (n = 10) against: HSP 70, 72, 27, neuronal polypeptides (alpha-MSH, NSE, bombesin, PGP 9.5, NGF, NGF-R) and intermediate filaments (peripherin, NF 200, CK 19, 20).

RESULTS

HSPs and alpha-MSH were upregulated in UV dermatitis in the epidermis compared to contact dermatitis and normal skin. Sunburn cells did not express HSPs or alpha-MSH in UV dermatitis. Neuronal markers and HSP 27 labeled more nerve fibers in UV than in contact dermatitis, except the increased staining for NGF, NGF-R and alpha-MSH in nerve fibers in contact dermatitis. In UV dermatitis, 50% of Merkel cells were suprabasal, but in contact dermatitis, basal, rounded and reduced in number.

CONCLUSIONS

Merkel cells, HSPs and markers of neuroinflammation are of different importance in UV and contact dermatitis in vivo.

Merkel cell hyperplasia in chronic radiation-damaged skin: its possible relationship to fibroepithelioma of Pinkus

Moderate hyperplasia of Merkel cells (MC) in chronic sun-damaged skin and hypertrophic actinic keratoses is well known. In the present study we investigated the number of MC in 24 samples of chronic radiation dermatitis and 19 cases of fibroepithelioma of Pinkus (FP), which is known to arise preferably in radiation-damaged skin. Using antibodies against the low molecular weight cytokeratins 8, 18, and 20 and chromogranin A to visualize MC, we found hyperplasia of MC in chronic radiation dermatitis. Additionally, in all FPs we could detect many MC, especially in areas with a pronounced fenestrated pattern. Recently, regulative functions of MC on the growth of follicular epithelium under various conditions were discussed. Thus, MC hyperplasia suggests a causal role also in the development of FP. In this context, hyperplasia of MC in chronic radiation dermatitis could explain the frequent occurrence of FP due to radiation exposure. As we recently found MC also in trichoblastomas but not in basal-cell carcinomas, the MC in FP may indicate its relationship to the benign trichoblastoma rather than to the basal-cell carcinoma. It is possible that regulative influences of the MC are important for the clinically rather benign course of FP.

Merkel cells are absent in basal cell carcinomas but frequently found in trichoblastomas. An immunohistochemical study

The possibility of a neuroendocrine differentiation in basal cell carcinomas (BCCs) has been a matter of debate for many years. In the present immunohistochemical study, applying the cytokeratins 8, 18 and 20 as the most established markers for Merkel cells (MCs), we did not find elevated numbers of MCs in any of 205 BCCs. This speaks against a neuroendocrine line of differentiation in BCCs. In contrast, we found various amounts of MCs in 15 of 36 trichoblastomas, which are the main benign differential diagnosis of BCC. In 4 trichoblastomas abundant MCs were spread over the whole epithelial tumor area. Additionally, the trichoblastomas' overlying epidermis exhibited significantly much higher numbers of MCs than the uninvolved adjacent skin or the epidermis overlying the BCCs. These findings might be an additional aid in the distinction between trichoblastomas and BCCs. Furthermore, concerning the recent discussion about the role of MC in growth and development of follicular germ, our observations are another sign of regulative influences of the MC, also in follicular germ under pathological conditions. Trichoblastomas with high numbers of MCs could be characterized as showing advanced differentiation toward the neuroendocrine component of the hair follicle, i.e., the MCs.

[Merkel cell and neuro-cutaneous system]

The Merkel cell is an epidermal neuroendocrine cell that can be identified by electron microscopy based on its neurosecretory granules or by immunolabeling based on its pattern of cytokeratin expression. Its origin is controversial but may be epidermal rather than neural. Although its functions have not been completely elucidated, there is strong evidence that it produces neuromediators, is involved in the perception of mechanical stimuli, exerts trophic and attractant effects on nerves, stimulates keratinocyte proliferation and differentiation, and plays a role in the spatial organization of the epidermis and epidermal appendages.

Differences of bcl-2 protein expression between Merkel cells and Merkel cell carcinomas

The bcl-2 gene, originally identified in B-cell lymphomas, encodes for proteins which may assume oncogenic functions by blocking apoptosis. Bcl-2 proteins are broadly distributed among various tissues, including epithelial ones. Within the skin, bcl-2 is strongly expressed in melanocytes, but its further distribution is yet unclear. The Merkel cells, neuroendocrine-epithelial cells of the skin, are present within the epidermis and hair follicles, mostly nerve-associated, and are believed to be postmitotic and long lived. Possibly they give rise to the malignant Merkel cell carcinomas. In the present study we investigated the bcl-2 expression on the protein level by means of immunohistochemical techniques including double confocal laser scanning microscopy, as well as on the RNA level by RT-PCR techniques, in Merkel cells, Merkel cell carcinomas, and cell lines. Merkel cells were identified by double staining for cytokeratins 20 or 8/18. We demonstrate that fetal epidermal and dermal Merkel cells are immunostained for bcl-2 protein, most of them clearly weaker than melanocytes. Adult Merkel cells also express bcl-2 protein very heterogeneously, mostly weak. In contrast, Merkel cell carcinomas are usually strongly positive for bcl-2 protein with some degree of heterogeneity. This is different from malignant melanomas in which bcl-2 expression is reduced as compared to normal melanocytes. Bcl-2 gene expression was also shown for Merkel cell carcinoma cell lines on both the mRNA and the protein level. Possibly bcl-2 protein expression is downregulated during the life span of Merkel cells, arguing that they may succumb to a certain cell turnover. The comparably high bcl-2 protein level in Merkel cell carcinomas may reflect peculiar biological and clinical characteristics.

Merkel cells in nevus sebaceus. An immunohistochemical study

Nevus sebaceus, considered to be a hamartoma, is known to develop several secondary hyperplastic and neoplastic proliferations. By the use of immunohistochemical studies, we were able to describe a sometimes very striking increase of Merkel cells in nine of 19 nevi sebacei. Only nevi sebacei that formed follicular germ structures and trichoblastomas showed a Merkel cell hyperplasia. In the hyperplastic epidermis of some cases a slight hyperplasia of singular Merkel cells was observed. In foci with follicular germs and trichoblastomas, however, the Merkel cells were much more abundant and sometimes arranged in clusters. Merkel cell hyperplasia is likely to represent another facet of hamartomatous hyperplasia in nevi sebacei. Our observation that trichoblastomas in nevus sebaceus possess, as a rule, hyperplasia of Merkel cells, might be an additional aid to distinguish these tumors from basal cell carcinomas, which are usually devoid of Merkel cells. Furthermore, our findings are a hint that development of follicular germs and trichoblastomas in nevi sebacei may be promoted by Merkel cells.

Merkel cells are integral constituents of desmoplastic trichoepithelioma: an immunohistochemical and electron microscopic study

The incidence of Merkel cells has previously been investigated in a number of inflammatory and tumorous lesions of the skin. Special attention was given to tumors with follicular differentiation. In the present study we examined the localization of Merkel cells in another adnexal tumor, the desmoplastic trichoepithelioma (n = 15), as well as in its main differential diagnosis, the morpheiform basal-cell carcinoma (n = 30). Using immunohistochemical methods, we found Merkel cells as a stable constituent in desmoplastic trichoepitheliomas, but failed to detect them in morpheiform basal-cell carcinomas. These findings might therefore be an important tool in the sometimes very difficult but clinically imperative distinction between these two conditions. Furthermore, our study may be of interest in the discussion about the origin of desmoplastic trichoepitheliomas. High numbers of Merkel cells in desmoplastic trichoepitheliomas indicate a bulge-derived origin of this adnexal tumor, since high numbers of Merkel cells, especially in the bulge, were recently discovered. Although the significance of Merkel cell hyperplasia in desmoplastic trichoepithelioma is not presently understood, a regulatory role of the Merkel cell in growth and development of this adnexal tumor is suggested.

Merkel cells do not require trophic maintenance from the nerves in adult human skin

A 34-year-old Japanese man with hereditary sensory neuropathy was examined to evaluate the distribution, density and inter-relationship between Merkel cells and peripheral nerves in the skin. An epidermal sheet of affected plantar skin showed numerous CAM 5.2-reactive Merkel cells, whereas PGP 9.5-reactive peripheral nerves were completely absent in the epidermis and dermis. These findings strongly suggest that Merkel cells do not require trophic maintenance from nerves in adult human skin.