The human cutaneous basement membrane--anchoring fibril complex: preparation and ultrastructure

Structural variations of collagen in normal and pathological tissues: role of electron microscopy

The spectrum of ultrastructural appearances assumed by collagen in normal and pathological tissues is illustrated using techniques of thin section transmission electron microscopy and computer-assisted analysis. The normal fibrillar collagen types are described in order to provide a basis for comparing other normal and abnormal forms. In normal tissues, the anchoring fibril and basal lamina (basement membrane) represent tissue structures largely containing collagen but differing significantly in organisation from normal types I to III fibrillar collagen. In pathological tissue, deviations from normal fine structure are reflected in abnormal aggregates of collagen fibrils (amianthoid and skeinoid fibres) and abnormalities in fibril diameter and cross-sectional profile. Fibrous and segment long-spacing collagen represent two further organisational variants of collagen, the former found widely in pathological tissues, the latter very rarely. Much remains to be discovered about these abnormal collagen variants-their mode of formation, the cells that produce them, and their roles. They also present a challenge for the collagen biologist formulating hypotheses of collagen fibril assembly and molecular organisation.

Distribution of type VII collagen in the epithelial basement membranes of mouse palate, tongue and lip mucosa

Dithiothreitol effectively separated the laminae densae and the laminae fibroreticulares of the basement membranes of oral mucosal epithelia as it does the epidermis and dermis. Dithiothreitol-separated epithelial basement membranes of palate, tongue, and lip were immunoreacted with colloidal gold-conjugated anti-type VII collagen antibody. By transmission electron microscopy, gold particles were observed only on the anchoring fibrils. For three-dimensional observation of the distribution of type VII collagen by scanning electron microscopy, secondary and backscattered electron images were compared. The secondary image showed the fine structure of the laminae densae and anchoring fibrils, and the backscattered images showed the gold particles conjugated with the antibody. By using an osmium conductive metal coating under optimal conditions, secondary and backscattered electron images of sufficient quality could be obtained. With the osmium coating, the backscattered electron image could show not only the gold particles but also the general morphological outline, making possible a comparison of the two images, which revealed the three-dimensional distribution of type VII collagen. Type VII collagen was also seen only on the anchoring fibrils, as in the epidermal basement membrane.

The structure of the interstitial surfaces of the epithelial basement membranes of mouse oral mucosa, gingiva and tongue

It is known that the gaps between epithelium and the underlying connective tissue usually occur between the epithelial cells and the basement membrane, resulting in exposure of the cellular surface of the lamina densa. After dithiothreitol separation, the epithelia of oral mucosa, gingiva, and tongue were mechanically peeled off from the underlying connective tissues. This treatment severed the connections between the basement membrane and the underlying connective tissue and the anchoring fibrils were pulled off from the collagen layer. In contrast, connections between the epithelial cells and basement membrane were preserved, resulting in exposure of the interstitial surfaces of the laminae densae. Scanning electron-microscopic observations of those interstitial surfaces were possible using the specimens prepared as above. The basement membranes of these three oral epithelia were morphologically the same not only by transmission but also by scanning electron microscopy. Scanning electron-microscopic observations revealed that their laminae densae were composed of fine fibrils and demonstrated three-dimensionally the projection of the anchoring fibrils from the laminae densae to the interstitial side. These findings coincide with those for epidermal basement membrane, which had already been observed with the same method.

Ontogenesis of the basement membrane zone after grafting cultured human epithelium: a morphologic and immunoelectron microscopic study

Sheets of cultured epithelial cells have been successfully used as autografts for the permanent coverage of patients with full-thickness burns and as allografts to stimulate the healing of chronic skin ulcers. The basement membrane zone (BMZ), composed of lamina lucida, lamina densa, and anchoring fibrils, plays a pivotal role in the firm adherence of the epidermis to the dermis. The present study describes the ultrastructural development during various stages of wound healing after resurfacing different wound areas by cultured epithelial grafts. For this purpose, biopsies were obtained from five patients 5 d to 4.5 years after resurfacing full-thickness burns with cultured autografts, and from five patients at various stages after treatment of excised tattoos and chronic skin ulcers with cultured allografts. One biopsy was taken from a spontaneously healed burn wound 30 years post-injury. Ultrathin sections were prepared for transmission and immunoelectron microscopy, using monoclonal antibodies against type IV and VII collagen. Findings were compared to controls of age- and site-matched normal skin. Eleven days after grafting, the first BMZ features had regenerated, including lamina lucida, a discontinuous lamina densa, hemidesmosomes, and sparse anchoring fibrils. The process of de novo synthesis of BMZ components had begun, and within 4 to 5 weeks complete reformation of BMZ was observed, including normal distribution of anchoring fibrils. Immunolabeling of type VII collagen was first observed upon the lower part of lamina densa at day 11 and steadily increased, reaching normal values 5 weeks after grafting. In contrast, gold deposition of type IV collagen upon lamina densa was strongly increased at day 19 compared to normal. This high expression reduced a little at 5 weeks, but remained high up to 30 years after injury. Long-term burn scars exhibited pseudopodia-like extensions of all basal cells, abundant anchoring fibrils, and an increased amount of arching anchoring fibrils. These features might compensate for the lack of proper rete ridges.

Ontogeny of structural components at the dermal-epidermal junction in human embryonic and fetal skin: the appearance of anchoring fibrils and type VII collagen

The ontogeny and composition of the dermal-epidermal junction (DEJ) in developing human embryonic and fetal skin was studied at progressive stages of gestation by immunofluorescence microscopy and immunocytochemistry using transmission electron microscopy (TEM). The DEJ of embryonic skin at 5 weeks estimated gestational age (EGA) was a simple basement membrane zone limited to the basal cell plasma membrane, lamina lucida, and lamina densa. A network of reticular collagen fibrils (reticular lamina) was deposited beneath the lamina densa by 6 weeks. Coincident with the onset of increased complexity in epidermal and dermal structure, at the time of the embryonic to fetal transition, the DEJ displayed additional components that were markers of maturation. At 7-8 weeks EGA, fine filamentous structures extended from the DEJ into the reticular lamina. By 9 weeks EGA hemidesmosomes and banded anchoring fibrils were recognizable, although distributed sparsely at the DEJ. With increasing gestational age, these structures displayed greater electron density and structural completeness. By the end of the first trimester, the DEJ appeared ultrastructurally similar to that of mature skin. Weak immunofluorescent labeling demonstrated the presence of type VII collagen at the DEJ by 8 weeks EGA. From 10-12 weeks EGA immunofluorescent labeling of the DEJ for type VII collagen was distinctly punctate, while immunoperoxidase labeling observed by TEM was linear, continuous, and sublamina densa in position. With ongoing gestation the immunofluorescent labeling became increasingly stronger at the DEJ. Thus, type VII collagen was present at the DEJ in the zone immediately beneath the lamina densa, before the appearance of mature anchoring fibrils but coordinate with the appearance of fine filamentous, unbanded structures, and appeared to increase with the development and accumulation of anchoring fibrils.

Tissue form of type VII collagen from human skin and dermal fibroblasts in culture

The triple-helical domain of type VII collagen was isolated from human placental membranes by mild digestion with pepsin, and polyclonal antibodies were raised in rabbits against this protein. After affinity purification the antibodies specifically recognized type VII collagen in both the triple-helical and the unfolded state. They also reacted with the fragments P1 and P2, derived from the triple-helical domain by further proteolysis with pepsin, but did not crossreact with other biochemical components of the dermal connective tissue. In skin the presence of a fragment of type VII collagen, similar to that isolated from placenta, was demonstrated by SDS-PAGE and immunoblotting. Type VII collagen represented less than 0.001% of the total collagen extracted by pepsin digestion from newborn or adult skin. The tissue form of type VII collagen was obtained from dermis after artificial epidermolysis with strongly denaturing buffers under conditions reducing disulfide bonds. The protein was identified by immunoblotting with the antibodies. The molecule was composed of three polypeptides with an apparent molecular mass of about 250 kDa, each. Similar large-molecular-mass chains could be identified by immunoblotting in extracts of human fibroblasts in culture.

Aged skin: a study by light, transmission electron, and scanning electron microscopy

The fine structural organization of the epidermis, dermal/epidermal junction, and dermis from an unexposed site (upper inner arm) of elderly people was compared with the organization of a similar region of young people. Despite an overall thinning of the epidermis and focal areas of cytologic atypia, the characteristic morphological markers associated with the keratinization process are not markedly altered in appearance or amount. A well-formed stratum corneum consisting of flattened, enucleated horny cells enveloped by a thickened membrane, and intracellular spaces filled with electron-dense material provide structural evidence that barrier ability is not compromised in senile skin. The dermal/epidermal changes in aged skin are marked and have significant physiologic implications. The major change is a relatively flat dermal/epidermal junction resulting from the retraction of the epidermal papillae as well as the microprojections of basal cells into the dermis. This flattening results in a more fragile epidermal/dermal interface and, consequently, the epidermis is less resistant to shearing forces. Retraction of the epidermal downgrowths (preferential sites of the putative epidermal stem cell) may also explain the loss in proliferative capacity associated with the aged epidermis. The three-dimensional arrangements of collagen and elastic fibers showed marked alterations with age. Both fibrous components appear more compact because of a decrease in spaces between the fibers. Collagen bundles appear to unravel, and the individual elastic fibers show signs of elastosis. These changes may contribute to the loss of resilience that is one of the salient features of senile skin.

Embryogenesis of the dermis in human skin

The process of human dermal development has been examined from the stage of the embryonic mesenchymal dermis (5-8 weeks of gestation) through the formation of the fibrous dermal connective (end of the first trimester), and during the growth of the fetal dermis (second and third trimesters) until birth. The elaboration of dermal organization and the overall increase in dermal thickness, largely consequences of extracellular, fibrous matrix accumulation, parallel the development and growth of the fetus as a whole. Although the mechanisms that determine the formation of the connective tissue architecture are not fully understood, the structural, histochemical, and biochemical changes that occur throughout development suggest processes that may be important in human dermal embryogenesis.

A study of the dermo-epidermal junction in dystrophic epidermolysis bullosa using the periodic acid-thiosemicarbazide-silver proteinate technique

Dermo-epidermal separation in dystrophic epidermolysis bullosa (DEB) is thought to results from an abnormality of anchoring fibrils which, in normal skin, are stained selectively by the periodic acid-thiosemicarbazide-silver proteinate technique. This method was applied to non-lesional skin from four patients with generalized recessive DEB, five with localized recessive DEB and one with dominant DEB. No anchoring fibrils were present in the subjects with generalized recessive DEB, but they were morphologically normal in the case of dominant DEB and in three patients with mild localized recessive DEB. Two patients with a more severe form of localized recessive DEB possessed attenuated anchoring fibrils which lacked the normal banding of the mid-portion. The lamina densa, normally unlabelled, was consistently stained in patients with generalized recessive DEB, suggesting a biochemical abnormality of this structure.

Evaluation of anchoring fibrils and other components of the dermal-epidermal junction in dystrophic epidermolysis bullosa by a quantitative ultrastructural technique

To examine the possibility that differences in the structure and population density of anchoring fibrils (AF) and other components of the dermal-epidermal junction might distinguish between genetically and clinically distinct varieties of dystrophic epidermolysis bullosa (DEB), a controlled ultrastructural morphometric study of nonseparated keratinocyte-associated dermal-epidermal junction was undertaken in a total of 17 patients with DEB. Seven patients had dominant DEB, 3 had localized recessive DEB, and 7 had severe, generalized recessive DEB. Nonlesional, unscarred skin was obtained from standard body regions. Criteria for the identification of AF were a mandatory union with the lamina densa and the presence of central banding and/or fanning of the extremities. No AF were detected in 9 technically suitable samples from patients with severe recessive DEB. Structurally normal AF were present, but significantly reduced in number, in both dominant and localized recessive DEB, compared with site-matched samples from 12 healthy adults. There was no difference in AF characteristics between dominant and localized recessive DEB, or between sites of predilection and nonpredilection for blisters. The presence or absence of albopapuloid lesions in dominant DEB did not influence AF counts. There was no difference in numbers of hemidesmosomes, basal cell plasmalemmal vesicles, or dermal microfibril bundles in any group of DEB patients compared with controls. Thus, although severe mutilating DEB can be distinguished by routine transmission electron microscopy, the dominant and localized recessive forms cannot be differentiated on the basis of AF structure or numbers.

Ultrastructural morphometry of normal human dermal-epidermal junction. The influence of age, sex, and body region on laminar and nonlaminar components

To obtain baseline data for future studies on such processes as wound healing, carcinogenesis, and blistering, a morphometric analysis of the dermal-epidermal junction was undertaken on normal skin from 3 or 4 standard sites on the arm and leg of 12 subjects aged 20-60 years. Lamina densa was thinner in females than in males (p less than 0.01) but no sex difference was apparent for lamina lucida. Both laminar elements were thinner beneath melanocytes than beneath keratinocytes. Sex, age, and body region had no apparent influence on numbers of hemidesmosomes or basal cell plasmalemmal vesicles, nor was there a significant variation of these structures among individuals. Numbers of dermal microfibril bundles diminished with age (p less than 0.01). Anchoring fibril counts varied widely both among individuals (p less than 0.025) and within the same subject; there were fewer in the upper arm compared with different parts of the leg (p less than 0.005). These results emphasize the importance of appropriate controls in studies of physiologic and pathologic conditions involving the dermal-epidermal junction.

Monoclonal antibodies to anchoring fibrils for the diagnosis of epidermolysis bullosa

Murine monoclonal antibodies to human anchoring fibrils reacted with human and monkey cervix, tongue, esophagus, and vagina. Rat, mouse, and guinea pig tissues were negative. In 11 patients with dystrophic recessive epidermolysis bullosa there was no reaction by immunofluorescence and immunoelectron microscopy. Other forms of epidermolysis bullosa had normal reactivity.

Epidermal-dermal junction during experimental skin carcinogenesis and cocarcinogenesis as revealed by scanning electron microscopy

During epidermal carcinogenesis important changes in the epidermal-dermal junction take place. Because of methodological difficulties may be these changes, especially those concerned with three-dimensional organization of the junction, remain unsatisfactorily investigated. To obtain new information, we studied with scanning electron microscopy (SEM) the development of carcinogenic changes in the epidermis of mice induced by DMBA-TPA, DMBA alone, and by the cocarcinogen TPA alone. We correlated the results with those from transmission electron microscopy and light microscopy. Although the epidermal changes morphologically showed similarities, biologically they differed. With them, distinct changes in the epidermal-dermal junction developed, that could be followed through early, hyperplastic and neoplastic phases. With the SEM the first changes were seen in the basal layer of the epidermis and concerned the cell arrangement. SEM provided information about the localization and development of incipient epidermal carcinomas induced by DMBA-TPA and DMBA treatment, as well as about the changes in the basal lamina. These can be classified by their surface, their extent and their frequency throughout large regions. Our studies indicate that these changes vary greatly, depending upon the treatment used and the time of their development. Only the progressive disintegration of the basal lamina is characteristic of carcinogenesis.

Immunohistochemical studies of the human cutaneous basement membrane-anchoring fibril complex

Antiserum to the human cutaneous basement membrane-anchoring fibril complex specifically binds to the basement membrane zone of normal human skin as demonstrated by indirect immunofluorescence and, in addition, cross-reacts with normal human glomerulus. This antiserum does not prevent binding of pemphigoid antibody to its specific antigen; thus the antigen of bullous pemphigoid is unlikely to be a component of the cutaneous basement membrane (basal lamina).