Basic histological structure and functions of facial skin

The skin and its appendages that derive from the epidermis (hair follicles, sweat glands, sebaceous glands, nails, and mammary glands) establish the integumentary system. Histologically, skin has two main layers—the epidermis and the dermis—with a subcutaneous fascia called the hypodermis, which lies deep in the dermis. The epidermis is formed of four to five layers of cells made mostly out of keratinocytes, along with three other different and less abundant cells. The dermis underlies the epidermis. The hypodermis is a looser connective tissue that is located beneath the dermis. It blends to the dermis with an unclear boundary.     

Eccrine sweat glands associate with the human hair follicle within a defined compartment of dermal white adipose tissue

It has always been assumed that sweat glands are distributed throughout the skin unconnected with hair follicles (hair “roots”) and their associated sebaceous (or “grease”) glands, which, together with other specialised glands and the muscles that make hairs stand up, are known as pilosebaceous units. Sweat glands and pilosebaceous units, in other words, have always been considered separate structures, with sweat glands opening on to the skin surface between hairs rather than alongside them. Sweat glands on the palms of the hands and the soles of the feet develop differently and were not considered in this study. Using a number of techniques, including looking down the microscope at sections of hair follicles taken from the scalp during hair transplants, and at manual and computer‐assisted 3D reconstructions of sections of scalp skin, this study from Spain and Manchester, UK, suggests that in hair‐bearing areas the deepest part of the sweat gland, a coiled structure, is in fact located very close to the deepest part of the pilosebaceous unit, sitting right by the sheath of the hair follicle, below the sebaceous gland and the point where the hair muscle attaches. Moreover, these structures sit together within cone‐shaped projections of fat that reach upwards into the lowest layer of the skin, the thick reticular dermis, from the fat underneath. The authors speculate that sweat glands, pilosebaceous units and this particular fatty tissue (collectively the “adnexal skin unit”) may interact in certain skin diseases, during wound healing and with drug treatments.     

THE USE OF AUTORADIOGRAPHY TO STUDY THE LOCALIZATION OF GERMICIDES IN SKIN

SUMMARY.— An autoradiographic technique for studying skin deposition and localization is described and applied to a study of germicides in surfactants. The method involves the use of unfixed frozen sections exposed to dry emulsion-coated slides.
The radioactive germicides carboxy-¹⁴C-3,4,4'-trichlorocarbanilide (TCC) in soap containing non-soap detergent (NSD) and zinc or zirconium pyridine-2-thione-1-N-oxide (PTO) in a shampoo were applied to the skin of guinea-pigs. Auto-radiograms of the skins showed that from soap, TGC was deposited on the stratum corneum, around the entrances to hair follicles, and was seen in the epidermis and dermis, but not in the follicles or sebaceous glands. From the NSD, TCC was seen in addition in the follicles and sebaceous glands. In one human subject, TCC from NSD was seen on the corneum, in the epidermis and dermis, hair follicles and sebaceous glands and also in the sweat glands. From the shampoo ZnPTO and ZrPTO were seen in guinea-pig skin on the corneum and in the follicles but whereas ZrPTO was in the epidermis and dermis, ZnPTO was not. In all vehicles the largest proportion of germicide was deposited on the corneum.
ZnPTO was shown to be soluble in sebum and to penetrate from sebum into only the hair follicles of guinea-pigs.
Scintillation counting of sections of guinea-pig skin treated with TCC, ZnPTO and ZrPTO supported the autoradiographic evidence that most of the germicide remained on the corneum.     

Histochemical localization of hyaluronan in psoriasis, allergic contact dermatitis and normal skin.

In suction blister fluid from active psoriatic lesions we have previously found elevated concentrations of hyaluronan. The aim of this investigation was to study the localization of hyaluronan with a histochemical method, in biopsy specimens from lesions of 13 patients with progressive psoriasis. Ten normal subjects and seven patients with allergic contact dermatitis were also studied. In normal epidermis the highest intensity of hyaluronan staining was found in the intercellular spaces in the middle and upper spinous layer, whereas the staining was much weaker in the basal layer. No hyaluronan was detected in the granular layer or in the orthokeratotic stratum corneum. In the dermis there was pronounced staining of the papillary dermis and around the sebaceous glands, sweat glands, hair follicles and blood vessels. In six of the 16 specimens from psoriatic lesions the normal epidermal meshwork of hyaluronan was partly absent and replaced by diffuse staining of both the spinous and the basal layer. In the remaining ten of these 16 specimens the same type of meshwork was found in stratum spinosum as in normal skin. The parakeratotic stratum corneum contained hyaluronan, in contrast to the normal stratum corneum, where no hyaluronan was present. The pattern of hyaluronan staining in the dermis of the psoriatic lesions did not differ from that in normal dermis. In the majority of the allergic patch test reactions the junction was less distinct than in normal skin between dermis and epidermis and the normal hyaluronan pattern of the basal layer was abolished and replaced by a diffuse staining throughout the layer.(ABSTRACT TRUNCATED AT 250 WORDS)     

Expression and localization of vascular endothelial growth factor and vascular endothelial growth factor receptor-2 in human epidermal appendages: a comparison study by immunofluorescence

Background.  Vascular endothelial growth factor (VEGF) promotes angiogenesis and plays important roles in neovascularization and development of tissues. VEGF receptors (VEGFRs) are high-affinity receptors for VEGF and are originally considered specific to endothelial cells. We have previously shown that keratinocytes from human normal skin express VEGFRs. This poses the question of whether these receptors are also expressed by epidermal appendages, as epidermal appendages are lined with epithelial cells.
Objective.  To investigate the expression of VEGFR-2 compare with VEGF in epidermal appendages, including hair follicles, eccrine sweat glands and sebaceous glands.
Methods.  Monoclonal antibodies to VEGF and VEGFR-2 were used for immunohistochemical examination of cryostat-cut sections of normal human skin specimens from 11 donors undergoing cosmetic surgery.
Results.  Immunoreactivities for VEGF and VEGFR-2 principally showed parallel intense expression in anagen hair follicle (including outer root sheat, inner root sheath, dermal papillae epidermal matrix), sebaceous glands (ductal and secretory portions) and eccrine sweat glands (ductal and secretory portions), respectively. In particular, abundant expression of VEGF was found in the follicular basement membrane zone surrounding the bulb matrix and in the ductal and secretory portions of eccrine sweat glands.
Conclusion.  A potential VEGF/VEGFR-2 autocrine pathway may be defined by the coexpression of VEGF and VEGFR-2 in human skin epidermal appendages.     

Expression pattern and intensity of protoporphyrin IX induced by liposomal 5-aminolevulinic acid in rat pilosebaceous unit throughout hair cycle

We have developed liposomal formulation of 5-aminolevulinic acid (ALA) to enhance topical delivery and examined ALA-induced protoporpyrin (PpIX) expression in rat pilosebaceous unit throughout hair cycle. Two types of liposomes—glycerol dilaulate (GDL) and phosphatidylcholine (PC)—were formulated and both liposomal ALA increased PpIX expression in rat dorsal skin and pilosebaceous units when compared with free ALA. However, iontophoresis combined with liposomal ALA reduced the expression intensity of PpIX in hair bulbs although it achieved deeper and wider expression of PpIX through transfollicular pathway. After topical application in intact or depilated rat skin, liposomal ALA produced excellent PpIX expression in pilosebaceous units. The expression pattern and intensity of PpIX changed in hair cycle-dependent manner: specific expression only in sebaceous glands was observed at telogen; strong expression in whole pilosebaceous units was shown at anagen with intense expressions in hair bulbs and sebaceous glands; and a pattern similar to anagen but reduced intensity in the hair bulbs was seen at catagen. Throughout hair cycle, the expression pattern and intensity were dramatically changed in hair follicular epithelial cells depending on the cell density and proliferation activity of those cells, whereas those were consistent in sebaceous glands regardless of hair cycle. Little expression was shown in dermis. Photoactivation effect of 20% liposomal ALA-PDT using a red filtered-halogen lamp damaged sebaceous glands, hair follicles and epidermal layers. Formation of a thicker epidermal layer was observed, and hair induction after depilation was inhibited along with damage in sebaceous glands.     

Fibronectin distribution during the development of fetal rat skin

Fibronectin distribution during fetal rat skin development has been studied immunocytochemically at the light and electron microscope level from 16 days of gestation to birth. The dermal-epidermal junction, the dermis, and connective tissue around developing muscle were shown by light microscopy to be heavily stained throughout this period. The development of hair follicles from about 18 days onward was not associated with any consistent change in fibronectin distribution. The heavy staining of the upper dermis was associated with a high density of mesenchymal cells, and immunoelectron microscopy revealed fibronectin on the surface of many of these cells and in association with the surrounding fine collagen fibrils. At the dermal-epidermal junction, both follicular and interfollicular, fibronectin was localized mainly in the plasma membrane and lamina lucida regions of the basement membrane, and there was also staining associated with the underlying fine collagen fibrils. These observations are further evidence for the proposed role of fibronectin as a mediator of the cell-matrix interactions which are of importance for tissue development and maintenance.     

Disulphide reaction staining for the identification of integumental elastic fibres

Based on specific methods (Sippel-APM-chromotropic acid technique; IC3-PE-maleimide fluorescence reaction) and skin samples of four domesticated mammals (dog, cattle, horse, pig), disulphide groups were demonstrated in the elastic component of the basement membrane of the epidermis, the elastic fibre system of the dermis, the elastic components of the connective tissue sheath of hair follicles, apocrine tubular glands, and sebaceous glands, and of the connective tissue surrounding the cutaneous muscle. The results are discussed regarding the relation of this reaction staining to the presence of microfibrils (fibrillin) in the elastic fibres.     

Is increased 5 alpha-reductase activity a primary phenomenon in androgen-dependent skin disorders?

Testosterone metabolism was investigated in fractions of human skin, enriched in epidermis, dermis, sebaceous glands, and sweat glands, by histologic sectioning of skin punch biopsies, and the results were compared with two culturable skin cells, i.e., keratinocytes and fibroblasts. Since sebocytes could not be brought in culture, metabolism was also investigated in the hamster flank model. In the epidermal tissue of the skin biopsies the predominant metabolite was androstenedione, formed by the enzyme 17 beta-hydroxysteroid dehydrogenase. The same was true for cultured hair follicle keratinocytes. In the deeper skin layers the formation of androstenedione was markedly reduced, whereas the formation of 5 alpha-reduced metabolites was highly increased, with a maximum in the skin fractions containing large sebaceous glands. Cultured shoulder skin fibroblasts showed a markedly different testosterone metabolism compared with the sectioned skin biopsies, suggesting that dermal fibroblasts play a less important role in the overall skin testosterone metabolism. The present approach, allowing the comparison of testosterone metabolism in different substructures of the same skin biopsy provides new evidence that the high 5 alpha-reductase activity in the specific skin fractions must be mainly ascribed to the sebaceous glands. These results render a previous hypothesis, stating that the elevated level of 5 alpha-reductase and subsequent formation of dihydrotestosterone in androgenetic alopecia and acne (usually accompanied by seborrhea) could therefore simply be the consequence of sebaceous gland enlargement, much stronger. This hypothesis is further evaluated by quantitative correlation of sebaceous gland size with enzyme activity in the hamster flank model.     

Distribution and expression of type VI collagen in photoaged skin

BACKGROUND: Several of the characteristic clinical features of photoaged skin, including wrinkling, are thought to be dependent on changes in the dermal matrix brought about by chronic sun exposure. Such changes include reductions in collagens I, III and VII, an increase in elastotic material in the reticular dermis and a marked reduction in the microfibrillar glycoprotein fibrillin. OBJECTIVES: To examine whether type VI collagen, a microfibrillar collagen necessary for cell-cell and cell-matrix communication, is affected by the photoageing process. METHODS: Six healthy volunteers with moderate to severe photoageing were enrolled into the study. Immunohistochemistry and in situ hybridization histochemistry were used to examine the levels of type VI collagen in photoprotected and photoaged sites. RESULTS: In photoprotected skin, type VI collagen was concentrated in the papillary dermis immediately below the dermal-epidermal junction, around blood vessels, hair follicles and glandular structures. The distribution of type VI collagen was unchanged in photoaged skin, although we observed an increase in the abundance of the alpha3 chain of collagen VI in the upper papillary dermis, at its junction with the dermal-epidermal junction (P < 0.05). No alterations were observed for any alpha chain at the mRNA level. CONCLUSIONS: These studies suggest that chronic sun exposure (photoageing) has little or no effect on either the distribution, abundance or levels of expression of type VI collagen in human skin. Thus, type VI collagen, unlike other matrix components so far studied, appears to be relatively unaffected by the photoageing process.     

Studies on fibronectin in the skin

Fibronectin is a glycoprotein mediating contact between cellular elements and collagen. As judged by indirect immunofluorescence studies fibronectin is abundantly present in normal human skin. It is located in the dermo-epidermal junction area, in the papillary and reticular dermis, about epidermal appendages (pilosebaceous units and eccrine sweat glands) and in the vascular and neural structures.     

Morphology of aged skin

Despite an overall thinning of the epidermis and focal areas of cytologic atypia, there was no morphologic evidence that the protective function of this tissue was compromised by age. The characteristic morphologic markers associated with the keratinization process were not altered either in appearance or in amounts. A well-formed stratum corneum was present, suggestive that barrier ability is not compromised in senile skin. Whereas alterations in the aged epidermis are slight, the dermal-epidermal changes are marked and have greater physiologic consequences. The major change is a relatively flat dermal-epidermal junction because of retraction of the epidermal papillae as well as the microprojections of basal cells into the dermis. This flattening results in a more fragile tissue less resistant to shearing forces. Retraction of the epidermal downgrowths may also explain the loss in proliferative capacity associated with the aged epidermis. The major alterations in the aged dermis concern the architecture of the collagen and elastin networks. Both fibrous components appear more compact because of a decrease in the voids or spaces between the fibers; the spaces resulted from a loss of ground substance. Collagen bundles appear to unravel, and the individual elastic fibers show signs of elastolysis. The net effect of these fibrous rearrangements and alterations is a dermis that is less stretchable, less resilient, more lax, and prone to wrinkling.     

Rat marrow-derived multipotent adult progenitor cells differentiate into skin epidermal cells in vivo

Wound repair and functional reconstruction are two key aspects for treatment of skin injury. Research on cell source for skin repair has become a focus of study. The immune rejection induced by allograft cells and the limited source of autologous epidermal stem cells have led to more attention on the multipotent adult progenitor cells (MAPC). In this study, we examined the influence of the local environment of skin injury on the migration and differentiation of MAPC in nude mice. The homing of MAPC to the wounds and the epidermal differentiation of MAPC were investigated by detecting the expression of specific antigens of rat major histocompatibility complex I (MHC-I) antigen and the tracing markers. Three weeks after transplantation, hair follicle-like structure appeared and rat MHC-I antigen was positive in the follicles of the healed skin. PKH26-labeled cells expressing cytokeratin were found in the regenerated follicle-like structures, sebaceous glands and sweat glands. Our findings indicate that MAPC can migrate to the skin injury site and the hair follicles, and participate in skin wound healing by differentiating into epidermal cells, which contributes to the theoretical research of MAPC plasticity and provides theoretical evidence for clinical application of transplantation therapy with MAPC.     

Expression patterns of programmed cell death 4 protein in normal human skin and some representative skin lesions

Expression of a tumor suppressor gene, programmed cell death 4 (PDCD4), was investigated at the protein level in the human skin. Immunohistochemically, PDCD4 protein expressed mainly in suprabasal layers, while PDCD4-positive and -negative areas were observed discontinuously in the basal cell layer of the epidermis. In hair follicles, the suprabulbar area including the hair and inner root sheath was immunoreactive, while the bulbar area, containing germinative cells which were strongly proliferating cell nuclear antigen (PCNA)-positive, was not or less. PDCD4 therefore appears to be important in the differentiation of hair follicles. PDCD4-positive cells were localized in the inside layers while PCNA-positive cells were located in the basal layer in the outer root sheath of hair follicles. The cells of sebaceous glands and sweat glands also were PDCD4-positive. The PDCD4 protein was localized mostly in nuclei of cutaneous cells. PDCD4 expression was found to be suppressed in the epidermis overlying an adult T-cell lymphoma (ATL), possibly reflecting a paracrine effect of factors produced by ATL cells. PDCD4 expression was suppressed in the keratinocyte cell line HaCaT by exposure of cultures to epidermal growth factor, transforming growth factor-beta1 or hepatocyte growth factor. Immunohistochemically, various skin cancers tended to show less PDCD4 expression than normal skin. Promotion of expression might prove useful in preventing or treating certain skin cancers.     

Expression of the small heat shock protein HSP 27 in developing human skin

The 27 kDa heat shock protein (HSP 27) is expressed in keratinocytes of the upper epidermal layers, and recent evidence suggests that this protein is involved in the regulation of epidermal differentiation. The expression of HSP 27 was investigated in developing human skin by immunohistochemistry utilizing a specific monoclonal antibody. We used formalin-fixed, paraffin-embedded tissue of abdominal skin obtained from 34 human fetuses ranging between 13 and 30 weeks estimated gestational age (EGA). We found that HSP 27 is not expressed in keratinocytes until week 14 EGA. At this stage staining is observed in the periderm and the upper intermediate cells but not in hair germs. During further development, HSP 27 expression correlates with increasing epidermal differentiation, i.e. shedding of the periderm and beginning of keratinization. HSP 27 expression is confined to the upper cell layers and sparse basal cells. In hair follicles, HSP 27 can be detected in the innermost cell layer of the outer root sheath and in keratinocytes of the bulge identical to what is observed in adult skin. The hair papilla, matrix cells and sebaceous glands are negative for HSP 27 and remain so during further development. In eccrine sweat glands of the 24th week EGA, HSP 27 is confined to the superficial cell layer of the sweat ducts. In the present report we demonstrate differentiation-related expression of HSP 27 in developing human skin. Further in vitro studies will address the molecular function of HSP 27 in epidermal differentiation and development.     

Immunohistochemical distribution of adult T-cell leukemia-derived factor/thioredoxin in epithelial components of normal and pathologic human skin conditions.

Tissues from normal human skin and various skin diseases were studied with the immunoperoxidase technique using an antibody to adult T-cell leukemia-derived factor (ADF), a homologue of human thioredoxin. Normal human skin showed positive immunostaining for ADF/thioredoxin in the outer root sheath of hair follicle, sebaceous glands, and secreting components of apocrine and eccrine sweat units, but not in the unexposed interfollicular epidermis and other parts of both hair follicles and the sweat units. Immunoreactivity of benign skin tumors gave similar distribution to their normal counterparts; trichilemmal cyst, nevus sebaceus, senile sebaceous hyperplasia, and mixed cell tumor were positive for immunostaining, whereas epidermal cyst and pilomatricoma were not. No immunoreactivity was detected in malignant skin tumors such as basal cell carcinoma and poorly differentiated squamous cell carcinoma. Solar keratosis, well-differentiated squamous cell carcinoma, some of metastatic lesions of squamous cell carcinoma, and extramammary Paget's disease reacted with the antibody. These immunoreactivities reflected numerous functions of thioredoxin in higher organisms. Our findings suggest that the expression of ADF/thioredoxin in both normal and abnormal human skin is related to epithelial cell differentiation.     

Analysis of the expression pattern of glial cell line-derived neurotrophic factor, neurturin, their cognate receptors GFRalpha-1 and GFRalpha-2, and a common signal transduction element c-Ret in the human scalp skin

BACKGROUND: Glial cell line-derived neurotrophic factor (GDNF) and a related family member, neurturin (NTN), as well as their cognate receptors (GDNF receptors, GFRalpha-1 and GFRalpha-2, respectively) are involved in nervous system development and murine hair cycle control. To date, their expression in human scalp skin is still unknown. MATERIALS AND METHODS: The expression pattern of these proteins was examined in human scalp skin by immunofluorescence and immunoalkaline phosphatase staining methods as well as RT-PCR (GDNF). A total of 50 normal human scalp skin biopsy specimens were examined (healthy females, 53-57 years). RESULTS: The expression of GDNF protein was strong in the epidermis and sebaceous and sweat glands. In the epidermis, GDNF protein expression was seen in all layers except the stratum corneum. It was strong in the basal layer and decreased gradually towards the granular layer. The results of RT-PCR analysis revealed that GDNF protein is synthesised in the epidermis. The expression of NTN, GFRalpha-1, and GFRalpha-2 proteins was strong in the papillary dermis and sebaceous and sweat glands. In the epidermis, NTN protein expression was absent. The expression of GFRalpha-1 and GFRalpha-2 proteins was moderate in the epidermis. The expression of c-Ret protein was consistently strong in the epidermis and sebaceous and sweat glands. These proteins were strongly expressed in both epithelial and mesenchymal compartments of human anagen VI scalp hair follicles. CONCLUSIONS: Our investigation reports, for the first time, the expression patterns of GDNF, NTN, GFRalpha-1, GFRalpha-2, and c-Ret proteins in human scalp skin. The expression of these proteins in the skin suggests their possible roles in skin homeostasis. The clinical ramifications of these observations mandate further investigations. Adly MA, Assaf HA, Hussein MR, Paus R. Analysis of the expression pattern of glial cell line-derived neurotrophic factor, neurturin, their cognate receptors GFRalpha-1 and GFRalpha-2, and a common signal transduction element c-Ret in the human scalp skin.     

Dermatologic diseases of the external ear

The external ear is composed of the auricle (pinna) and the external auditory canal. Both of these structures contain elastic cartilage (except the earlobe) and a small amount of subcutaneous fat, which are covered by skin. The skin of the cartilaginous canal contains hair cells, sebaceous (lipid-producing) glands, and apocrine (ceruminous) glands; this is in contrast with the osseous canal, which contains neither glands nor hair follicles.     

The Spectrum of Epidermal Nevi: A Case of Verrucous Epidermal Nevus Contiguous with Nevus Sebaceus

During the normal development of skin, pluripotential cells give rise to keratinocytes, sebaceous glands, hair follicles, apocrine glands, and eccrine glands. In epidermal nevi, these components emerge in an abnormal mixture within a circumscribed site. Many authors have categorized epidermal nevi based on their predominant component; however, there is often notable overlap that occurs within a single area or within contiguous areas. We report a verrucous epidermal nevus contiguous to a nevus sebaceus of Jadassohn. The categories of epidermal nevi are somewhat artificial. Our case supports the view that epidermal nevi have a spectrum of manifestations, including verrucous epidermal nevi and nevus sebaceus of Jadassohn.     

Expression of ɛBP, a β-galactoside-binding soluble lectin, in normal and neoplastic epidermis

Abstract The study of animal lectins and glycoconjugates has become an important area of research in biomedical sciences, as these molecules are believed to play important roles in a variety of biological processes. This report describes a study of the expression of an animal lectin, IgE-binding protein (?BP), also known as Mac-2 and CBP35, in human skin. We have analyzed cultured human keratinocytes as well as normal human skin and a number of epidermal neoplasms, by immunoblotting. immuno-fluorescence and immunohistochemistry. We showed that ?BP is expressed in human keratinocytes, hair follicles, sebaceous and sweat glands. We found that cBP expression retains in various epidermal neoplasms, including basal cell carcinoma, squamous cell carcinoma and keratoacan-thoma, although the level of expression appears to be reduced as compared to normal epidermis. The immunohistochemical analysis also suggests that the level of ?BP expression appears to be dependent on the degree of cellular differentiation of keratinocytes.