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Background: Hidradenitis suppurativa/acne inversa is an inflammatory, debilitating disease for which wide local excision of the affected area with secondary wound healing is considered the treatment of first choice for the inactive scarring form or after adequate anti-inflammatory medical treatment., Objectives: In this study, we aimed to assess the duration of complete secondary wound healing after surgical intervention for hidradenitis suppurativa/acne inversa., Materials & Methods: Twenty-three surgical procedures in 17 consecutive patients (eight female, nine male) were evaluated for duration of secondary wound healing at axillary or anogenital/inguinal sites. To investigate the contribution of hair follicle bulge progenitor cells in wound re-epithelialization, tissue samples of lesional and perilesional skin were analysed for expression of the stem cell marker, cytokeratin 15 (CK15), and CD200, a marker for human follicular stem cells that resides in the bulge area., Results: Initial wound size did not differ significantly between surgical wounds in the axillary (mean: 30.0 cm 2  ± 5.4) and anogenital/inguinal (mean: 35.3 cm 2  ± 5.7) region. However, healing time to complete wound closure was almost twice as fast in the anogenital/inguinal (mean: 132 days ± 10.4) than axilla area (mean: 254 days ± 39.1; p < 0.01). The accelerated wound healing in the anogenital/inguinal region was accompanied by significantly enhanced CK15 and CD200 expression, compared to axillary wounds (p < 0.05)., Conclusion: The anogenital/inguinal region showed significantly faster secondary wound healing after surgical intervention for hidradenitis suppurativa/acne inversa compared to axillary wounds. We suspect differences in pilosebaceous unit density and thus hair follicle progenitor cells (as mirrored by CK15 and CD200 expression) to be the main driver behind this finding.

Background: Body region-dependent hair follicle (HF) characteristics are concerned with follicular size and distribution, and have been demonstrated to have characteristics for each region of the body., Objectives: The aim of the present study was to investigate the expression patterns of the markers called cytokeratin 15 (K15), cytokeratin 6 (K6) and monoclonal antibody Ki-67, and also apoptosis in HFs, which can be observed in different parts of the human body., Material and Methods: In this study, healthy human HFs were taken by biopsy from 5 various donor sites of the human body: the scalp, the leg, the abdomen, the back and waist. HF-containing skin specimens taken using cryosection were stained with hematoxylin & eosin (H&E) and K15, K6, Ki-67 and terminal deoxynucleotidyl transferase-mediated digoxigenin-dNTP nick end-labelling (TUNEL) immunofluorescence staining protocol was performed., Results: Different skin regions from the human body were examined histologically. While the HFs of scalp tissue showed anatomically obvious hair layers, some hair sections from other regions, like the leg, the abdomen, back and waist, were not as distinct as in the scalp region. According to our findings, K15 expression was highest in the scalp. In addition, the immunoreactivity (IR) intensity of K15 was significantly decreased in the HFs on the waist and abdominal regions, compared to the scalp and back regions (p < 0.001). However, the IR intensity of K6 in the scalp region was statistically significantly higher than the IR intensity of K6 in the abdomen region (p < 0.05). Moreover, we showed intraepithelial apoptosis and proliferation of keratinocytes in the bulge of HF. In the study, Ki-67-positive and TUNEL-positive cell numbers were not statistically significant (p > 0.05)., Conclusions: Our findings are important for further investigation of molecular aspects of the human hair follicle stem cells compartments in health and disease, which might be a promising model for comparative studies with different human diseases.

Epithelial-to-mesenchymal transition (EMT) is critical for embryonic development and wound healing, and occurs in fibrotic disease and carcinoma. Here, we show that EMT also occurs within the bulge, the epithelial stem cell (eSC) niche of human scalp hair follicles, during the inflammatory permanent alopecia, lichen planopilaris. We show that a molecular EMT signature can be experimentally induced in healthy human eSCs in situ by antagonizing E-cadherin, combined with transforming growth factor-β1, epidermal growth factor, and IFN-γ administration, which to our knowledge has not been reported previously. Moreover, induction of EMT within primary human eSCs can be prevented and even partially reversed ex vivo by peroxisome proliferator-activated receptor-γ agonists, likely through suppression of the transforming growth factor-β signaling pathway. Furthermore, we show that peroxisome proliferator-activated receptor-γ agonists also attenuates the EMT signature even in lesional lichen planopilaris hair follicles ex vivo. We introduce lichen planopilaris as a model disease for pathological EMT in human adult eSCs, report a preclinical assay for therapeutically manipulating eSC EMT within a healthy human (mini-)organ, and show that peroxisome proliferator-activated receptor-γ agonists are promising agents for suppressing and partially reversing EMT in human hair follicles eSCs ex vivo, including in lichen planopilaris., (Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.)

The paper presents an example of an immunohistochemical study of malignancy in oral epithelial hyperplasia. In the described case in view of the difficulty in determining the onset of the epithelial malignancy with the usual histological technique, an immunohistochemical method was used with antibodies to proteins Ki-67, human papillomavirus (HPV) type 16 and cytokeratin 15. The results of immunohistochemical study indicated increased proliferative activity of epithelial cells, presence of papillomavirus HPV16 in their cytoplasm and synthesis of cytokeratin 15 in all layers of the epithelium. These characteristics of squamous intraepithelial neoplasia may be a diagnostic criterion for the beginning of oral epithelial malignization.

Purpose: To further study the mechanism of epithelization on the fascia side of the flap after surgical incision and the treatment of the negative pressure therapy., Methods: With the patients' informed consent, parts of tissue samples were obtained from a 51-year-old diabetic patient who was suffering lower extremity ulcers. The samples were processed with hematoxylin and eosin (HE) staining and Masson trichrome staining. The keratin 19, keratin 15 and carcino-embryonic antigen (CEA) were immunohistochemically detected., Results: The results of HE staining showed that the specimen was divided into two regions, newborn area and original epithelial area. There were more inflammatory cells infiltrating in the dermis in the newborn epithelial area, compared with the original epithelial area. Cells in newborn epithelial area were more active and many dinuclear and polynuclear cells were observed in newborn epithelial area. But there were more cuticular layers and obvious rete pegs in original epithelial area. In addition, the cells with keratin 19 and CEA positive were found around hair follicle, while keratin 15 was negative. Masson trichrome staining showed that there was a lot of de novo collagen in newborn epithelial area., Conclusion: Epidermal cells on the fascia side of the flap could be derived from the stem cells. Negative pressure wound therapy would attract not only cells but also other elements such as growth factors, cytokines, some nutrients and extracellular matrix. With the formation of the appropriate microenvironment after debridement, the migrated cells can grow, differentiate and spread, eventually leading to the epithelization on the fascia side of the flap in diabetic foot., (Copyright © 2017. Production and hosting by Elsevier B.V.)

Background: Cytokeratins (CK) belong to the family of intermediate filament proteins, and among them specific epithelial keratins are considered markers for stem cells activation., Objectives: This study aims to investigate the expression of CK15 and CK19 as possible stem cell markers in vitiligo during phototherapy., Methods: The study was conducted on vitiligo patients receiving narrow-band ultraviolet therapy. Immunohistochemical staining for CK15 and CK19 was carried out, and clinical follow-up continued for 4 weeks., Results: Of 28 patients, CK15 expression was demonstrated in 17 cases (61%) while CK19 expression was demonstrated in 11 cases (39%). Cells expressing positive staining were demonstrated in follicular and interfollicular epithelium. Expression was clearly demonstrated in patients younger than 20 years old, with shorter disease duration, with disease stability, and with normally pigmented hairs. Expression of cytokeratins was significantly correlated to improvement of vitiligo lesions., Conclusion: CK15 and CK19 are expressed in vitiligo during UV repigmentation in the follicular and interfollicular epithelium. This expression of cytokeratins was significantly correlated to improvement and can be considered valuable tool to monitor stem cells stimulation for the sake of the repigmentation process in vitiligo., (© 2016 Wiley Periodicals, Inc.)

Keratin 5 (K5) is a marker of basal progenitor cells in the epithelia of a number of organs. During prenatal development of the submandibular gland (SMG) in mice, K5(+) progenitor cells in the developing epithelia play important roles in its organogenesis. Although K5(+) cells are also present in the adult mouse SMG and may function in tissue regeneration, their histological localization has not yet investigated in detail. In the present study, we examined the immunohistochemical localization of K5 in the SMG in adult and postnatal developing mice. At birth, K5 immunoreactivity was detected in the entire duct system, in which it was localized in the basal cells of a double-layered epithelium, but was not detected in the terminal tubule or myoepithelial cells. At postnatal weeks 1-3, with the development of intercalated ducts (ID), striated ducts (SD), and excretory ducts (ED), K5-immunoreactive basal cells were gradually restricted to the ED and the proximal double-layered portions of the ID connecting to the SD. At the same time, K5 immunoreactivity appeared in myoepithelial cells, in which its positive ratio gradually increased. In adults, K5 immunoreactivity was localized to most myoepithelial cells, most basal cells in the ED, and a small number of ID cells at the boundary between the ID and SD in the female SMG or between the ID and granular convoluted tubules in the male SMG. These results suggest that K5 is a marker of differentiated myoepithelial cells and duct progenitor cells in the mouse SMG.

Functional hair follicle (HF) stem cells (SCs) are crucial to maintain the constant recurring growth of hair. In mice and humans, SC subpopulations with different biomarker expression profiles have been identified in discrete anatomic compartments of the HF. The rare studies investigating canine HF SCs have shown similarities in biomarker expression profiles to that of mouse and human SCs. The aim of our study was to broaden the current repertoire of SC-associated markers and their expression patterns in the dog. We combined analyses on the expression levels of CD34, K15, Sox9, CD200, Nestin, LGR5 and LGR6 in canine skin using RT-qPCR, the corresponding proteins in dog skin lysates, and their expression patterns in canine HFs using immunohistochemistry. Using validated antibodies, we were able to define the location of CD34, Sox9, Keratin15, LGR5 and Nestin in canine HFs and confirm that all tested biomarkers are expressed in canine skin. Our results show similarities between the expression profile of canine, human and mouse HF SC markers. This repertoire of biomarkers will allow us to conduct functional studies and investigate alterations in the canine SC compartment of different diseases, like alopecia or skin cancer with the possibility to extend relevant findings to human patients., (© 2016 The Histochemical Society.)

The study of cytoskeleton arrangement and its contribution to survival of cell-to-cell contacts appears to be essential for understanding of numerous cellular and tissue processes. Applying CK15, S100 labeling and TUNEL reaction to cutaneous lichen planus subtypes, we found CK15 expression in the outer and inner root sheath of hair follicles, the basal epidermal layer, and eccrine glands. Its follicular expression was decreased in nearby inflammatory infiltrates. The CK15 immunopositivity was mostly described as weak (92.3%) for lichen planus but equally subdivided into weak, moderate and strong in lichen planopilaris (2 = 32.514; df = 4; p < 0.001). The greatly varying apoptotic index was the highest in the lichen planopilaris involving the scalp: 81.2 ±10.7; 87.8 ±10.7 and 88.0 ±10.5 for the basal, spinous and upper epidermal layers, respectively. S100 positive epidermal and follicular cells did not differ in the lesions demonstrated in the study groups; still immunoreactivity was more pronounced in the scalp region of lichen planopilaris. Damage of cell-to-cell contacts was confirmed by electron microscopy. Apart from immunocyte-mediated keratinocyte death, cytoskeleton-based injury and loss of cell-to-cell and matrix contacts may be of great importance, leading to eradication of degrading cells and thus contributing to the pathogenesis of lichen planus.

Adenoid cystic carcinoma (ACC) can arise in several organs, and prognosis is highly dependent on the primary tumor site. Primary cutaneous ACC has an excellent prognosis compared with salivary or lacrimal ACC. Activation of MYB by gene fusion or other mechanisms has been found in salivary, breast, and lacrimal ACCs but has not been described in cutaneous ACC. We analyzed the histopathologic and immunohistochemical features of 19 primary cutaneous ACCs, 2 periorbital ACCs, and 12 salivary gland ACCs and assessed for MYB activation in primary cutaneous ACC by immunohistochemistry and molecular methods. The presence of perineural invasion differed significantly among ACCs of various sites (83% salivary, 50% eyelid, 11% skin, P=0.0002). Over 90% of all ACCs were grade 1 or 2 and exhibited diffuse (>50%) positivity with CD117, SOX-10, and smooth muscle actin immunostains. CK15 and vimentin showed diffuse positivity in 36% and 57% of cutaneous ACCs, respectively, and were negative or only focally positive in all salivary ACCs (P=0.04 and 0.002). Six of the 11 cutaneous and periorbital ACCs tested with reverse transcriptase polymerase chain reaction and/or fluorescence in situ hybridization had MYB rearrangements including 2 cases that expressed MYB-NFIB fusion transcripts. Diffuse expression of MYB protein assessed by immunostaining was present in 8 of 9 cutaneous ACCs, including cases both with and without MYB rearrangements. These results indicate that cutaneous ACCs possess the same types of MYB alterations as ACCs of other anatomic sites. Vimentin and CK15 appear to have some discriminatory value in differentiating between primary cutaneous and salivary gland ACCs.

The histogenesis of Merkel cell carcinoma (MCC) has remained unresolved. Moreover, one of the questions is whether pure MCC and combined MCC represent the same histogenesis and entity. The existence of combined MCC suggests that MCC likely arise from pluripotent stem cells. Merkel cells (MC) localize within the bulge area, which is populated by hair follicle stem cells. We used hair follicle stem cell markers to investigate whether MCC share certain characteristics of these stem cells. Fourteen MCC specimens were examined histologically and immunohistochemically. There were six pure MCC and eight combined MCC. In six combined MCC, both MCC components and squamous components at least focally shared the expression of one or more of cytokeratin (CK)15, CK19 and CD200, which are hair follicle stem cell markers. On the other hand, four cases of pure MCC showed partially distinct CK19 expression, but did not show CK15 and/or CD200 expression. There was a distinct difference between pure MCC and combined MCC on the expression of hair follicle stem cell markers. The normal skin expressed CK15, CK19 and CD200 in the bulge area, whereas CK15 and CD200 were absent in the MC-rich glabrous skin and touch domes. The results led us to hypothesize that combined MCC originate from the hair follicle stem cells. We postulate that combined MCC undergo multidirectional differentiation into squamous, glandular, mesenchymal and Merkel cells. Further investigation is warranted to confirm the histogenesis of pure MCC and combined MCC., (© 2015 Japanese Dermatological Association.)

Objective: The identification of stem cells (SC) remains challenging. In the human oral mucosal epithelium, these cells are believed to be in the basal layer (stem cell niche), but their exact location is unclear. The aim of this study was to examine the dysplastic oral epithelium for these SC-like proteins in order to assess their diagnostic value as biomarkers complementing the histological grading of dysplasia., Material and Methods: Thirty oral epithelial dysplasia (OED), 25 oral lichen planus (OLP), 10 oral hyperkeratosis and 5 normal oral epithelium (OE) were immunohistochemically examined for four SC markers [integrin β1, neuron-glial-2 (NG2), notch 1 (N1) and keratin 15 (K15)]., Results: Three of four SC markers were heterogeneously detected in all samples. K15 overexpression in the lower two-thirds of severe OED suggests an expanded SC niche. Integrin β1 distribution pattern was not measurably different between OEDs and control. NG2 was almost negative to absent in all samples examined. N1 expression was weak and highly variable in normal and dysplastic epithelium, making it an unreliable epithelial stem cell marker., Conclusions: Present findings suggest that these markers were unable to identify individual epithelial stem cells. Instead, subpopulations of cells, most probably stem cells and transit amplifying cells with stem cell-like properties were identified in the dysplastic oral epithelium. The characteristic expressions of K15 might be of diagnostic value for oral dysplasia and should be investigated further.

Objective: To characterize the subtypes of ameloblastoma by differentiation markers., Study Design: Expression of 9 major acidic epithelial keratins was immunohistochemically examined in 28 ameloblastomas., Results: Keratin 15 (K15) expression patterns corresponded to histological variants: follicular, plexiform and acanthomatous. Tumor nests comprising K15-expressing basal cells mimicked oral epithelium or dental lamina, and tumor nests comprising K15-negative basal cells mimicked outer enamel epithelium. Keratin 19 (K19) was consistently expressed in solid/multicystic ameloblastoma and unicystic ameloblastoma, while peripheral ameloblastoma and desmoplastic ameloblastoma contained K19-negative cells., Conclusions: The 4 current subtypes had unvaried expression patterns within each group. However, they could be divided into 2 groups by K19 expression pattern: solid/multicystic and unicystic versus extraosseous/peripheral and desmoplastic. K15 expression pattern represented various types of differentiation for tumor nests mimicking tooth germ and oral epithelium. The results clarify the homogeneity and heterogeneity of ameloblastoma cell lineage and differentiation., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Recent work has focused on the hair follicle as the main source of multipotent stem cells in the skin. The hair follicle bulge contains multipotent stem cells that can form the epidermis, hair follicles and sebaceous glands and help in repopulation of the epidermis after injury. The localization of these stem cells to the bulge area may explain why some types of inflammatory alopecia cause permanent loss of hair (cicatricial alopecia) (such as lichen planopilaris and discoid lupus erythematosus), while others (such as alopecia areata) are reversible (noncicatricial alopecia). The lack of distinctive bulge morphology in human hair follicles has hampered studies of bulge cells. To date, the best marker for bulge stem cells in human hair is cytokeratin (CK) 15; human bulge cells have been reported to express CK15 selectively throughout all stages of the hair cycle in different types of follicles. There is direct evidence in the mouse, and indirect evidence in the human, that compromising the integrity of the sebaceous gland and/or bulge is important in the development of alopecia. Several interesting studies have been done in the last few years to investigate the role of stem cells in alopecia, especially nonscarring types. This is a review about the role of stem cells in the pathogenesis of alopecia (scarring and nonscarring)., (© 2012 The Author. BJD © 2012 British Association of Dermatologists.)

Background: The overlap in histopathologic features and immunoprofile of eccrine and apocrine neoplasms confounds basic issues relating to lineage of these entities., Methods: We evaluated expression of follicular stem-cell markers, cytokeratin (CK) 15 and nestin, in 78 benign and 23 malignant adnexal neoplasms., Results: CK15 and nestin expression were noted in 39 of 78 (50%) and 36 of 78 (46%) cases in the benign group, respectively (8 cutaneous mixed tumor, 10 hidradenoma papilliferum, 9 apocrine cystadenoma, 11 cylindroma and/or spiradenoma, and 9 poroma/dermal duct tumor). CK15 and nestin expression were noted in 11 of 23 (48%) and 7 of 23 (30%) cases in the malignant group, respectively (6 microcystic adnexal carcinoma, 7 porocarcinoma, and 9 eccrine carcinoma). Except 1, both markers were negative in 4 syringocystadenoma papilliferum, 10 hidradenoma, 1 syringofibroadenoma, 10 syringoma, 1 eccrine adenoma, 8 poroma/dermal duct tumor, 5 eccrine hidrocystoma, and 1 apocrine carcinoma., Conclusions: Given that follicular germinative cells give rise to the folliculosebaceous apocrine unit, expression of CK15 and nestin in the majority of cutaneous mixed tumor, hidradenoma papilliferum, apocrine cystadenoma, and cylindroma/spiradenoma is suggestive of an apocrine origin/differentiation of these neoplasms. Reinforcing this and a novel finding of our study is the preferential expression of nestin in myoepithelial cells of these lesions.

The aim of this study was to analyse the hitherto largely unknown expression patterns of some specific cellular and extracellular molecules during palate and nasal cavity development. We showed that epithelia of the developing palate and the vomerine epithelium express similar sets of structural proteins. With the exception of keratin 15, which becomes barely detectable in the elevated palatal shelves, nearly all of these proteins become upregulated at the presumptive areas of fusion and in the adhering epithelia of the palate and nasal septum. In vivo and in vitro analyses indicated that reduction in the amount of keratin 15 protein is independent of Tgfbeta-Alk5 signalling. Foxa1 expression also highlighted the regionalization of the palatal and nasal epithelia. Owing to the lack of reliable markers of the palatal periderm, the fate of peridermal cells has been controversial. We identified LewisX/stage-specific embryonic antigen-1 as a specific peridermal marker, and showed that numerous peridermal cells remain trapped in the medial epithelial seam (MES). The fate of these cells is probably apoptosis together with the rest of the MES cells, as we provided strong evidence for this event. Heparan sulphate, chondroitin-6-sulphate, and versican displayed dynamically changing distribution patterns. The hitherto-unknown innervation pattern of the developing palate was revealed. These findings may be of value for unravelling the pathogenesis of palatal clefting.

Nestin, a marker of neural stem cells, is expressed in the stem cells of the mouse hair follicle. The nestin-expressing hair follicle stem cells give rise to the outer-root sheath. Nestin-expressing hair follicle stem cells that are negative for the keratinocyte marker keratin 15 (K15) can differentiate into neurons, glia, keratinocytes, smooth muscle cells, and melanocytes in vitro. Recent studies suggest that the epithelial stem cells are important in tumorigenesis. In this study, we immunohistochemically examined the expression of three hair follicle stem cell and progenitor cell markers, nestin, K15, and CD34, in normal human epidermis and hair follicles and in epidermal and follicular tumors, trichilemmoma, basal cell carcinoma (BCC), and squamous cell carcinoma (SCC). In normal human skin, the cells in the epidermal basal layer were positive for K15 and negative for nestin and CD34. The hair follicle cells below the sebaceous glands were also positive for nestin and K15 and negative for CD34. The outer-root sheath cells under this area could be divided into three parts: an upper part of the outer-root sheath cells that was partially positive for nestin and positive for K15 and negative for CD34; a middle part that was CD34-positive and K15-negative; and a lower part that was positive for K15 and negative for CD34. In the tumor tissues, nestin immunoreactivity was observed in trichilemmoma but not in BCC. Also, immunoreactivity for K15 was strong in BCC and weak in trichilemmoma, and SCC was negative for nestin and partially positive for K15. No CD34 immunoreactivity was observed in any of the cases. These results suggested that trichilemmoma originates in the nestin-positive/K15-positive/CD34-negative outer-root sheath cells below sebaceous glands, BCC tumor cells from the more mature nestin-negative/K15-positive/CD34-negative outer-root sheath cells, and SCC from the nestin-negative/K15-positive/CD34-negative keratinocytes of the basal cell layer in the epidermis.

Trichoepithelioma (TE) is a benign neoplasm of the skin that resembles basal cell carcinoma (BCC) in its clinical and histological features. In this study, we evaluate the usefulness of elastic fiber staining and cytokeratin 15 expression pattern in terms of distinguishing TE from BCC. Eleven TE and 17 BCC were examined histochemically and immunohistochemically. It was found that BCC contain more elastic fiber than TE, and that more TE show peripheral localization than BCC in cytokeratin 15 expression patterns. The present study shows that elastic fiber staining and cytokeratin 15 expression pattern may aid the differentiation of TE from BCC.

Even though immunohistochemical comparisons of microcystic adnexal carcinoma vs infiltrative basal cell carcinoma and desmoplastic trichoepithelioma exist, they are mostly restricted to the use of a single stain. In addition, a comparison with squamous cell carcinoma has not been reported previously. In this study, we compare the expression of cytokeratin (CK) 15, CK7, CK20, CK903, carcinoembryonic antigen (CEA), CD10, CD15 and BerEP4 in 13 microcystic adnexal carcinoma, eight desmoplastic trichoepithelioma, 10 infiltrative basal cell carcinoma, and eight squamous cell carcinoma of which five exhibited ductal differentiation. We found that the majority of microcystic adnexal carcinoma (92%) and desmoplastic trichoepithelioma (100%) cases expressed CK15 while the infiltrative basal cell carcinoma and squamous cell carcinoma cases were all negative. Forty percent of infiltrative basal cell carcinoma expressed CK7; while only two microcystic adnexal carcinoma cases (15%) and one squamous cell carcinoma with ductal differentiation (12%) expressed CK7 in the remaining three tumor categories. None of the desmoplastic trichoepithelioma expressed CK7. All tumors were strongly positive for CK903. While the neoplastic cells were negative, luminal staining of ductal structures was noted for CK7, CD15 and CEA in some of the microcystic adnexal carcinoma, desmoplastic trichoepithelioma and squamous cell carcinoma with ductal differentiation cases. Sixty percent of infiltrative basal cell carcinoma, 31% of microcystic adnexal carcinoma, and 25% of squamous cell carcinoma express CD10. BerEP4 expression was noted in 38% of microcystic adnexal carcinoma, 57% of desmoplastic trichoepithelioma, 100% of infiltrative basal cell carcinoma, and 38% of squamous cell carcinoma. In conclusion, we found CK15 to be a useful marker in distinguishing microcystic adnexal carcinoma from infiltrative basal cell carcinoma and squamous cell carcinoma with ductal differentiation. Our experience indicates that microcystic adnexal carcinoma and desmoplastic trichoepithelioma have a similar immunohistochemical profile that is, CK15+ and BerEP4+/-; thus, additional studies are needed to separate these two entities.

Acute graft-versus-host disease (GVHD) conceptually may be divided into three evolutionary stages: allostimulation, effector cell homing to specific tissues, and cellular targeting and injury. Surprisingly, little is known regarding the targeting stage of GVHD. Recently, we have learned that epithelial target cell injury is mediated by specific subpopulations of effector T cells that may be identified based on Vbeta family expansion during allostimulation. Antibody probes specific for these Vbeta families have permitted precise identification of effector cell homing patterns. In squamous epithelium, allospecific T cells selectively home to basal cell layer subpopulations that express cytokeratin 15 (CK15) and that undergo target cell injury via apoptosis. Interestingly, these target cells coincide with basal layer subpopulations that have properties of epithelial stem cells and that normally express an apoptosis-resistant genomic profile. Accordingly, epithelial cell injury in GVHD appears to involve selective targeting of stem-cell subpopulations via conversion from an anti-apoptotic to a pro-apoptotic phenotype. Understanding of the mechanism(s) of this conversion could facilitate development of translationally relevant approaches to shielding target cells from injury in GVHD. Moreover, determination of how putative apoptosis-resistant stem cells may be rendered vulnerable to immune-mediated targeting has implications potentially relevant to more directed immunotherapeutic approaches focused at elimination of neoplastic (cancer) stem cells.

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.

Recent works demonstrated the presence of a multipotent epithelial cell population in the bulge region of adult human hair follicles. These cells can be cultured in vitro, thus leading to the preparation of dermal-epidermal substitutes which are applicable in the treatment of burns and ulcers. We evaluated the main marker expression in cells obtained from stripped human hair follicles. A pool of hair follicles were incubated at 37 degrees C and 5% CO(2) in a growth medium. The cells were then labelled with antibodies (anti-CD34, anti-CD38, anti-CD45, anti-CD90, anti-CD133, anti-CD146) and analysed by cytometry. We also used hair follicles for immunohistochemical studies, employing antibodies such as CD34, Actin Smooth Muscle, Filaggrin, Desmin, Vimentin, Glial Fibrillary Acidic Protein, Ki-67, PanCytokeratin, CK15, CK19. The cytometry results revealed that a part of bulge cells were CD34+ (1-2%). CD34+ population comprises both large, CD45-, CD133-, CD146- cells and small, CD45+, CD133+, CD146+ cells. Thus, a part of CD34+ cells present a mature endothelial marker (CD146). An expression of the proliferation marker Ki-67 and the stem cell marker CD34 is present in the follicle bulge region. In conclusion, we observed that the stripped hair follicle has the same multipotent cell population as adult and fetal scalp hair follicles.

The normal gene expression profile of rete-tip keratinocytes targeted in human graft-versus-host disease (GVHD) remains unexplored. Murine lingual epithelium, unlike murine skin, consists of a basal layer that resembles human cutaneous rete ridges and harbors rete tip-associated cells that express cytokeratin 15 (K15), a marker for epithelial stem cells. Target cell apoptosis in murine GVHD preferentially involves subpopulations of basal cells that (1) reside at tips of lingual rete ridge-like prominences (RLPs), (2) constitutively express K15 protein, (3) express the proapoptotic protein Bax early in disease progression, and (4) coincide spatially with putative epithelial stem cells. Here, we show by real-time reverse transcription-PCR that immunohistochemistry-guided laser-captured K15-positive (K15+) murine basal cells constitutively express quantitatively higher mRNA levels for K15 but lower mRNA levels of Bax than do K15- basal cells, consistent with the presumed stem cell nature of K15+ basal cells. Moreover, apoptosis gene array screening of K15+ microdissected basal cells demonstrated a dominant trend toward the preferential expression of genes associated with protection from apoptosis. Accordingly, genes that regulate apoptotic vulnerability are differentially expressed in basal layer subpopulations distinguishable by K15 expression.