Immunohistochemical study of human eccrine sweat ducts with anti-keratin antibodies. Presence of a layer between luminal and peripheral cell layers

New concepts on the histogenesis of eccrine neoplasia from keratin expression in the normal eccrine gland, syringoma and poroma

BACKGROUND

Peripheral and luminal layers of eccrine sweat gland ducts are self-renewing structures. Proliferation is restricted to the lowermost luminal layer, but randomly scattered in the peripheral layer. Each layer exhibits differential expression of keratins K5/K14 and K6/K16. Keratin K1 occurs only in peripheral cells and the novel keratin K77 is specific for luminal cells.

OBJECTIVES

To investigate the expression of luminal (K77), peripheral (K1) and further discriminatory keratins in two eccrine sweat gland tumours: syringoma, thought to show differentiation towards luminal cells of intraepidermal sweat ducts and eccrine poroma, considered to arise from poroid cells, i.e. peripheral duct cells; and keratinocytes of the lower acrosyringium/sweat duct ridge differentiating towards cells of intradermal/intraepidermal duct segments.

METHODS

Paraffin-embedded sections were examined by immunohistochemistry using several keratin, smooth muscle actin and Ki-67 antibodies.

RESULTS

We confirmed the ductal nature of syringomas. Despite drastic morphological alterations in both layers, their keratin patterns remained almost undisturbed compared with normal ducts. In eccrine poroma epidermal keratins K5/K14 were ubiquitously expressed in all poroid cells. Cell islands deviating morphologically from poroid cells contained epidermal keratins K1/K10. K77 expression was limited to luminal cells of intact duct structures within the tumours.

CONCLUSIONS

Syringomas are benign tumours of luminal cells of the lowermost intraglandular sweat duct. Poroid precursor cells of poromas do not comprise peripheral duct cells nor do poromas differentiate towards peripheral or luminal duct cells. Instead, poroid cells consist only of keratinocytes of the lowermost acrosyringium and the sweat duct ridge and poromas tend to differentiate towards the cells of the upper acrosyringium.

Are Sweat Glands an Alternate Penetration Pathway? Understanding the Morphological Complexity of the Axillary Sweat Gland Apparatus

To build an effective barrier against the penetration of extrinsic agents is one of the skin's main functions. The barrier properties of the stratum corneum and the epidermis have been subject to extensive studies in the past while the role of skin appendages as possible pathways of penetration are only rarely described. In order to study the possible penetration barriers in these complex appendages, a careful investigation of their morphology and ultrastructure has to be done. Studying the morphology of axillary skin appendages requires clear-cut criteria for the differentiation between eccrine, apocrine and apoeccrine glands. Therefore we studied the distribution of proteins described to be specific for either eccrine or apocrine glands (CD15, CD44, S-100 and milk fat globulin) on axillary skin samples from healthy young adults by immunofluorescence. Additionally, we examined the distribution of cytoskeletal proteins such as cytokeratins (1/10/11, 14, 18) and F-actin. For a more detailed understanding of the possible versatile barrier elements of the axillary sweat glands, we studied the distribution of tight-junction-associated proteins (occludin, claudin 1, claudin 4). The coils and the dermal duct may provide an active barrier built of tight junctions as occludin and claudin 4 are co-localized. However, the intra-epidermal duct did not show any co-localization of the investigated proteins. By combining morphological features as revealed by F-actin staining and the distribution of the above-mentioned proteins, immunocytochemical typing of eccrine and apocrine glands becomes possible. With this tool, we could also confirm the existence of apoeccrine glands and locate them in their 'natural environment'.

Characterization of a novel human type II epithelial keratin K1b, specifically expressed in eccrine sweat glands

In this study, we show that a novel human type II epithelial keratin, K1b, is exclusively expressed in luminal duct cells of eccrine sweat glands. Taking this luminal K1b expression as a reference, we have used antibodies against a plethora of epithelial keratins to systematically investigate their expression in the secretory globule and the two-layered sweat duct, which was divided into the intraglandular, intradermal, and intraepidermal (acrosyringium) segments, the latter being further subdivided into the sweat duct ridge and upper intraepidermal duct. We show that (i) each of the eccrine sweat gland tissue compartments expresses their own keratin patterns, (ii) the peripheral and luminal duct layers exhibit a sequential keratin expression, with both representing self-renewing cell layers, (iii) the intradermal duct and the sweat duct ridge display hitherto unknown length variations, and (iv) out of all cell layers, the luminal cell layer is the most robust layer and expresses the highest number of keratins, these being concentrated at the apical side of the cells to form the cuticle. We provide evidence that the cellular and intercellular properties of the peripheral and the luminal layers reflect adaptations to different functions.

Eccrine syringofibroadenoma (Mascaro): an immunohistochemical study

Eccrine syringofibroadenoma is an uncommon benign eccrine tumor, which was first described by Mascaro in 1963. It usually develops on the extremities of elderly persons. We report on a 74-year-old man who presented with a 2-year history of a slowly growing lesion on his face. A detailed histologic and immunohistochemical study was performed on the biopsy material. The tumor consisted of epidermal-derived anastomosing thin epithelial cords embedded in a fibrovascular stroma. The epithelial cords contained ductal and cystic structures lined by luminal cells, which were decorated by antibodies against carcinoembryonic antigen, keratin K19, K8, and K18. Antibody to keratin K6 decorated the luminal walls of the acrosyringia. Antibodies to filaggrin decorated the superficial luminal structures. These results suggest dual acrosyringial and dermal duct differentiation in syringofibroadenoma.

Differentiation of eccrine poroma cells to cytokeratin 1- and 10-expressing cells, the intermediate layer cells of eccrine sweat duct, in the tumor cell nests

It has been shown that an intermediate cell layer exists between a luminal cell layer and a peripheral cell layer in human eccrine sweat ducts by immunohistochemistry using anti-keratin antibodies 34 beta B4 and DE-K10. These antibodies react to cytokeratin 1 and 10 respectively, and stain the intermediate cells specifically, but not luminal cells nor peripheral cells. Cytokeratin 1 and 10 are considered to appear as a differentiated keratin in the terminal process of epidermal keratinization. We examined 5 cases of eccrine poroma with 34 beta B4 and DE-K10. Various numbers of the poroid cells reacted to these anti-keratin antibodies in 4 cases. Some positive cells were observed around the cuticular cells in two of them. The present study demonstrated that terminal differentiation in terms of keratinization can occur in eccrine poromas, and that the 34 beta B4- and DE-K10-positive cells around the cuticular cells differentiate toward the intermediate cells in cytokeratin expression profile and location.

Eccrine syringofibroadenoma (Mascaro). An ultrastructural and immunohistochemical study

Eccrine syringofibroadenoma is a rare benign skin tumor, which usually develops on the extremities of elderly persons. We performed immunohistochemical and ultrastructural studies of a typical case of eccrine syringofibroadenoma that developed on the left heel of a 58-year-old man. The tumor consisted of anastomosing thin epithelial strands connected to the epidermis. There were many ductal or cystic structures, and their luminal cells were strongly positive to antibodies against carcinoembryonic antigen and epithelial membrane antigen. Filagrin and involucrin immunoreactivities were also detected in some cells surrounding the ducts. Keratins K1 and K10, co-expressed in the peripheral cells of normal acrosyringia, were colocalized in small cell clusters. Ultrastructurally, intracellular duct formation characteristic of developing acrosyringia was observed. Tumor cells containing globular keratohyaline granules with various electron densities were seen around some ductal structures. In these areas, keratinization took place without lamellar granule formation or prominent cornified cell envelope assembly. These results suggest acrosyringial differentiation of this tumor.

Distribution of metallothionein in normal and pathological human skin

The expression and distribution of metallothionein (MT) in frozen sections of normal and pathological human skin was studied using the monoclonal antibody L2E3 directed against MT derived from human fetal liver. Immunohistochemical staining of normal fetal and adult skin revealed strong reactivity in basal keratinocytes of epidermis and outer hair root sheath, hair matrix cells and the secretory coil, but not the exocrine portion of eccrine glands; myoepithelial cells around apocrine sweat glands were similarly stained. In epidermal hyperplasia, variable numbers of suprabasal keratinocytes were stained, whereas in interface dermatitis, interrupted staining was found in the basal layer. Weak or scattered staining was observed in squamous tumours, whereas basal cell carcinomas did not show consistent staining. The distribution of MT in normal skin was in line with the germinative role of basal keratinocytes and hair matrix cells, whereas its distribution in hyperplastic epidermis was in line with experimental animal data, and reflected the increase in the germinative pool in these conditions. It is concluded that monoclonal antibody L2E3 may serve as a valuable immunohistochemical marker in diagnostic cutaneous pathology since it labels basal keratinocytes selectively, and since it discriminates between eccrine and apocrine sweat glands.

Selective involvement of keratins K1 and K10 in the cytoskeletal abnormality of epidermolytic hyperkeratosis (bullous congenital ichthyosiform erythroderma)

Aggregation of tonofilaments within epidermal keratinocytes is a characteristic histologic feature of epidermolytic hyperkeratosis including the generalized form known as bullous congenital ichthyosiform erythroderma. The histologic distribution and the keratin composition of the altered tonofilaments were investigated to determine whether the aggregation was specific to any particular keratin(s). Skin samples from seven patients and one mid-trimester fetus with generalized epidermolytic hyperkeratosis, and from one patient with a localized or "nevoid" form of epidermolytic hyperkeratosis, were analyzed by using various microscopical and immunocytochemical methods. A conjunctival sample and cultured epidermal keratinocytes from one patient with generalized epidermolytic hyperkeratosis were also examined by electron microscopy and immunocytochemistry. Ultrastructurally, tonofilament aggregates were distributed within the suprabasal stratified epithelial cell layers of the epidermis, of the infundibular part of outer root sheaths, and of the sebaceous ducts and sweat ducts, selectively following the known distribution pattern of keratins K1 and K10. The abnormal tonofilaments were not found in any other cutaneous epithelia, in conjunctival epithelium, or in cultured keratinocytes, where K1 and K10 are absent or only minimally expressed. Immunoelectron microscopy showed that among the keratins detected in suprabasal epidermolytic hyperkeratosis epidermis (K1/K5/K10/K14/K16), the aggregated tonofilaments predominantly expressed K1 and K10 rather than other keratins. These results suggest that the keratin filament abnormality in epidermolytic hyperkeratosis principally involves K1 and K10 and raise the question whether epidermolytic hyperkeratosis might be primarily a disorder of one or both of these keratins.