Ultrastructural studies of human gingiva. 3. Changes of the basal lamina in chronic periodontitis

Matrix Metalloproteinases in the Periodontium-Vital in Tissue Turnover and Unfortunate in Periodontitis

The extracellular matrix (ECM) is a complex non-cellular three-dimensional macromolecular network present within all tissues and organs, forming the foundation on which cells sit, and composed of proteins (such as collagen), glycosaminoglycans, proteoglycans, minerals, and water. The ECM provides a fundamental framework for the cellular constituents of tissue and biochemical support to surrounding cells. The ECM is a highly dynamic structure that is constantly being remodeled. Matrix metalloproteinases (MMPs) are among the most important proteolytic enzymes of the ECM and are capable of degrading all ECM molecules. MMPs play a relevant role in physiological as well as pathological processes; MMPs participate in embryogenesis, morphogenesis, wound healing, and tissue remodeling, and therefore, their impaired activity may result in several problems. MMP activity is also associated with chronic inflammation, tissue breakdown, fibrosis, and cancer invasion and metastasis. The periodontium is a unique anatomical site, composed of a variety of connective tissues, created by the ECM. During periodontitis, a chronic inflammation affecting the periodontium, increased presence and activity of MMPs is observed, resulting in irreversible losses of periodontal tissues. MMP expression and activity may be controlled in various ways, one of which is the inhibition of their activity by an endogenous group of tissue inhibitors of metalloproteinases (TIMPs), as well as reversion-inducing cysteine-rich protein with Kazal motifs (RECK).

Epithelium-Specific Runx2 knockout mice display junctional epithelium and alveolar bone defects

OBJECTIVE

The aim of this investigation was to study the effects of Runt-related transcription factor 2 (Runx2) on the junctional epithelium and alveolar bone.

METHODS

The attachment level of the junctional epithelium and the resorption of alveolar bone were analyzed by histology and scanning electron microscopy. The expression of amelotin was determined by immunohistochemistry, Western blot, and real-time PCR. The ultrastructure of the dentogingival interface was observed by transmission electron microscopy.

RESULTS

The cKO mice demonstrated remarkable attachment loss, epithelial hyperplasia, and alveolar bone loss. The relative protein and mRNA expression of amelotin was increased in the junctional epithelium of the cKO mice. The attachment apparatus of the cKO mice showed ultrastructural deficiency.

CONCLUSIONS

Loss of Runx2 led to the junctional epithelium and alveolar bone defects in mice. Runx2 may play a crucial role in maintaining the integrity of the dentogingival junction and the normal structure of alveolar bone.

Lipopolysaccharide induces a stromal-epithelial signalling axis in a rat model of chronic periodontitis

AIM

Lipopolysaccharide is a bacterial virulence factor implicated in chronic periodontitis, which may penetrate the junctional epithelial barrier and basement membrane to insult underlying stroma. We sought to identify lipopolysaccharide-induced global gene expression changes responsible for signalling between stroma and epithelium during disease onset.

MATERIALS AND METHODS

Using a rat lipopolysaccharide periodontitis model, junctional epithelium and underlying stromal tissue were separately collected from healthy and diseased animals by laser-capture microdissection and subject to gene expression microarray analysis. Key gene products identified were validated in gingival epithelial and fibroblast cell cultures.

RESULTS

Global gene expression patterns distinguishing health versus disease were found in and between both tissue types. In stroma, the most significantly altered gene ontology function group (Z ≥ 4.00) was cytokines, containing most significantly (±2-fold; p < 0.05) upregulated genes amphiregulin, IL1-β and Fas ligand, all positive, diffusible modulators of the epithelial growth factor receptor pathway. In epithelium, the most significant changes were in downregulated FOS-related antigen-1 gene, somatostatin receptor-2 gene and mucin-4 gene, all negative modulators of the epithelial growth factor receptor pathway.

CONCLUSION

These results establish a periodontitis model for studying gene product interactions and suggests that the onset of junctional epithelial disease hyperproliferation involves a concerted stromal-epithelial signalling axis.

Ultrastructure and composition of basement membranes in the tooth

The tooth, the hardest organ in the body, is known to be formed through highly elaborate, unique processes of differentiation and development. Basement membranes play critical roles in fundamentally important biological processes such as growth and differentiation, and for better understanding of the mechanism of development and maintenance of the tooth, specializations of tooth basement membranes are reviewed in detail in relation to their roles. The basement membrane at such diverse locations in the tooth as the inner enamel epithelium, maturation-stage ameloblasts, and junctional epithelium at the dentogingival border are specialized in their own highly unique ways for anchoring, firm binding, or mediation in the transport of substances. Thus, the role of basement membranes in the developing and mature tooth is manifold and for these roles individual basement membranes are specialized in their own specific ways which are rare or not seen in nondental tissues, and these specializations are essential for successful development and maintenance of the tooth.

Detection and possible biological role of chondroitinase and heparitinase enzymes produced by Porphyromonas gingivalis W50

Gingival crevicular fluid levels of the glycosaminoglycan (GAG) chondroitin-4-sulphate (C-4-S) have received increased attention as potential indicators of periodontal tissue turnover. However, little is known about the relationship between crevicular fluid connective tissue metabolites and microbial factors. In this study Porphyromonas gingivalis, a periodontopathogen, was investigated for its ability to degrade the GAGs C-4-S, dermatan sulphate (DS) and heparan sulphate (HS) in vitro. The effect of P. gingivalis extracts on the proteoglycans (PG) derived from human gingiva were also investigated. The presence of chondroitinase and heparitinase eliminase enzymes were identified from the vesicle fraction of P. gingivalis W50. These enzymes were extracted from the vesicle fraction by a differential centrifugation technique and partially purified by non-denaturing gel filtration chromatography which revealed heparitinase enzyme peaks at 200 and 150 kDa and chondroitinase at 70 kDa. Gingival proteoglycans for use as substrates were purified using 4 M guanidinium chloride extraction and anion exchange chromatography; these proteoglycans contained 48% DS, 27% C-4-S and 13% HS P. gingivalis chondroitinase and heparitinase enzymes were capable of the degradation of C-4-S and HS but not DS GAGs. The presence of chondroitinase enzymes produced by P. gingivalis may influence levels of connective tissue metabolites in crevicular fluid. Furthermore these enzymes, particularly the heparitinase, may be involved in the initial permeation of the gingival epithelium, permitting the ingress of further microbial virulence factors.

Ultrastructural characterization of internal basement membrane of junctional epithelium at dentogingival border

BACKGROUND

Although a number of electron microscopic observations of the dentogingival border have been reported, observation of the detailed ultrastructure of the internal basement membrane of the junctional epithelium at the border has not yet been done.

METHODS

The internal basement membrane of a rhesus monkey (Macaca mulatta) was ultrastructurally characterized with high-resolution electron microscopy. The head and neck region of a 5-year-old animal was perfused with a fixative containing 1.25% glutaraldehyde, 0.75% formaldehyde, and 0.04% CaCl2 in 0.1 M phosphate buffer, pH 7.4. Isolated mandibular segments were further fixed with 2.5% glutaraldehyde, 2% formaldehyde, and CaCl2 (300 mg/l) in 0.1 M sodium cacodylate buffer, pH 7.4, for 24 hr at 4 degrees C. The segments were then demineralized and cut into small pieces that were postfixed with 1% osmium tetroxide and further processed for electron microscopy.

RESULTS

The internal basement membrane takes the form of both a common basement membrane and, in places, a multilayered basement membrane. This basement membrane was found to have fundamental ultrastructural features common to other basement membranes. That is, the bulk of the basement membrane is composed of a network of irregular anastomosing strands referred to as "cords." Heparan sulfate proteoglycan-containing ribbonlike 4.5-5-nm-wide "double tracks" were also present in this basement membrane. However, the lamina densa of this basement membrane was unusually thick (160 nm) compared with the thickness (30-60 nm) in other basement membranes, and the cords were also much thicker (8.3 +/- 1.9 nm vs. the usual 3-5 nm).

CONCLUSIONS

From these results, it is concluded that this particular basement membrane is specialized for mechanical strength. This specialization is likely to be suitable for the purpose of the tight sealing of the periodontal tissues from the oral environment.

Keratinocyte integrins in wound healing and chronic inflammation of the human periodontium

Periodontal epithelium plays a critical role in protection, destruction and repair of human periodontium. During optimal repair, epithelium migrates and covers the wound surface to prevent infection and damage of the vulnerable underlying connective tissue. During periodontal destruction, junctional epithelium undergoes transformation to pocket epithelium that has quite different characteristics from junctional epithelium. In the course of periodontal disease the epithelial attachment to the tooth surface is lost and the epithelium proliferates and extends pseudo-rete ridges deep into the inflamed connective tissue. Both scenarios, repair and destruction, involve active epithelial migration either in the wound provisional matrix or in the inflamed connective tissue matrix, respectively. This review covers recent research data on cellular receptors, integrins, that mediate epithelial cell migration during wound healing and destruction of human periodontium.

Multilayer culture of periodontal ligament epithelial cells: a model for junctional epithelium

The unique features of junctional epithelium involve lack of keratinization, limited differentiation and a relatively permeable structure. In order to study the relationship between differentiation and permeability of stratified epithelium a model system was developed. Porcine periodontal ligament epithelial cells were cultured on the polycarbonate nucleopore membrane of the Transwell two-compartment culture system. Within 5 days of culture the cells formed a confluent multilayered structure. Subsequently, maturation of the structure and differentiation of surface cells took place. Transmission electron microscopy showed that the cells were arranged into basal and suprabasal layers with sparse desmosomal attachments and wide intercellular spaces resembling the organization of junctional epithelium. The basal cells attached to a subepithelial basal lamina through numerous hemidesmosomes. The cytokeratin profile of the cultured epithelium (K5, 6, 14, 16, 19) resembled that of the cells of junctional epithelium attached to the tooth surface. The older cultures expressed differentiation markers, K4, K13 and involucrin, thereby resembling sulcular epithelium. The epithelial permeability, measured by diffusion of phenol red, radioactive dextran or methionine tracers, and as transepithelial electrical resistance, decreased with the increased cell number and maturation of the cultures. The new model provides an organotypic culture system which allows to control differentiation of a multilayered periodontal epithelium. It thus may serve as a valuable new tool for studies on the permeability and behaviour of periodontal epithelium under the influence of exogenous and endogenous factors.

Expression of fibronectin and integrins in cultured periodontal ligament epithelial cells

The process of attachment of epithelial cells obtained from the porcine periodontal ligament (cell rests of Malassez) to different extracellular matrix proteins and their expression of fibronectin and integrin receptors were studied by means of immunocytochemistry, in situ hybridization, and time-lapse cinemicrography techniques. The cell lines of periodontal ligament epithelial cells (PLE cells) attached to and spread rapidly on fibronectin, vitronectin, and type I collagen. One of the cell lines also attached to laminin, while the other cell line showed poor attachment to both laminin and Matrigel, a basement membrane material. By use of the in situ hybridization technique, some PLE cells were found to express the fibronectin gene strongly. Immunocytochemical staining localized fibronectin in extracellular fibrils and intracellular granules. Fibronectin was also found in the tracks left behind by the cells migrating on the substratum. Arg-gly-asp-ser peptide inhibited the attachment of the PLE cells to fibronectin, laminin, type I collagen, and vitronectin by 47%, 43%, 83%, and 94%, respectively, suggesting that the cell-matrix interactions were partly mediated by receptors related to the integrin family. Antibodies against the beta 1-integrin subunit stained the cell bodies and the plasma membrane projections of spreading cells. After 24 h or longer in culture, beta 1-integrins were localized to the regions of cell-cell contact. Cinemicrography of the arg-gly-asp-ser-peptide-treated cells demonstrated that the spreading and migration of isolated cells were prevented by the peptide. The peptide did not appear to dissociate the cell-cell contacts or interfere with migration of spread-cell colonies.(ABSTRACT TRUNCATED AT 250 WORDS)

Genesis of hadacidin-induced cleft palate in hamster: morphogenesis, electron microscopy, and determination of DNA synthesis, cAMP, and enzyme acid phosphatase

A morphological, electron microscopic, and biochemical study was undertaken to analyze the genesis of hadacidin-induced cleft palate in hamster fetuses. Gross and light microscopic observations indicated that hadacidin affected the growth of vertical palatal shelves to induce cleft palate. Electron microscopic observations showed that initial hadacidin-induced changes were seen in the mesenchymal cells. Within 12 hr of drug administration, the perinuclear space was swollen and a lysosomal response injury was evident in the mesenchymal cells. Subsequently, 24 hr after hadacidin treatment, lysosomes appeared in the epithelial cells; changes were also seen in the basal lamina which included separation of the lamina densa from the basal cells, duplication of lamina densa, and complete loss of basal lamina. Between 36 and 42 hr post-treatment, the cellular and basal lamina changes subsided, and the epithelium of vertical shelves underwent stratification. Biochemical determination of enzyme acid phosphatase indicated that the levels of enzyme activity in both the control and treated palatal tissues corresponded to the appearance of lysosomes. Measurement of cAMP levels suggested that the peak activity of cAMP corresponded to that of enzyme acid phosphatase and cell injury. The cAMP activity in hadacidin-injured cells, however, was significantly lower in comparison to that of the dying cells of control palates. Hadacidin treatment also affected DNA synthesis in the developing primordia of the palate. It was suggested that hadacidin injures the precursor cells of the palate prior to the appearance of the primordia, and subsequently affects their proliferative behavior, stunting the vertical growth of the palatal shelves and inducing a cleft palate.

Immunohistochemical distribution of the collagen types IV, V, VI and glycoprotein laminin in the healthy rat, marmoset (Callithrix jacchus) and human gingivae

The purpose of this study was to demonstrate the localization of collagen types IV, V and VI as well as the glycoprotein laminin in biopsies of healthy rat, marmoset (Callithrix jacchus) and human gingivae. The slices, after the use of indirect immunofluorescence (incubation with antibodies against these extracellular matrix components), showed the same distribution with the anti-type IV and laminin antibodies on the basement membranes of the epithelium, blood vessels and nerves. Collagen type V, as a filamentous, and collagen type VI, as microfibrillar components, were localized in a similar pattern in the different species. In contrast to the other species, collagen type VI could not be found near the basement membranes of vessels and nerves of the marmoset gingiva. This result shows differences between human and monkey tissues, but not between rat and human gingivae, and conforms the heterogeneity of collagen type VI in the various cell and tissue types.

Gross and cellular analysis of 6-mercaptopurine-induced cleft palate in hamster

The present study analyzes the morphological, histochemical, and ultrastructural aspects of the pathogenesis of 6-mercaptopurine (6MP)-induced cleft palate in hamster fetuses. Gross and light microscopic observations indicated that 6MP stunts the growth of vertical palatal shelves and thus induces cleft palate. Ultrastructural analysis showed that, in contrast to controls, 6MP-induced alterations were first seen in the mesenchymal cells 24 hr after drug administration. The initial alterations were characterized by swelling of the nuclear membrane. During the next 12 hr, lysosomes were seen first in the mesenchymal cells and then in the cells of the medial edge epithelium (MEE) of the developing palatal primordia. The appearance of lysosomes was temporally abnormal and was interpreted as a sublethal response to 6MP treatment. Subsequently, the nuclear alterations and the lysosomes diminished; and 48 hr after 6MP administration, they were absent from the palatal tissues. Ninety hours after 6MP administration, unlike the controls (in which the palatal shelves were already fused), changes were seen at the epithelial-mesenchymal interface in the developing cleft palatal shelves. These changes were characterized by breakdown of the basal lamina and epithelial-mesenchymal contacts. Eventually, at term, the MEE of the vertical shelf stratified. It was suggested that 6MP affected cytodifferentiation in the palatal tissues during the critical phase of early vertical shelf development and thereby induced cleft palate.

An in vitro model to study bacterial invasion of periodontal tissues

In periodontal disease, the abilities of bacteria to adhere to and degrade in vivo basement membranes should be considered as two of the rate-limiting steps for the potential active or passive invasion of gingival connective tissues. To study these mechanisms in greater detail, we used the PF HR-9 basement-membrane-like matrix to establish an in vitro model of bacterial invasion and degradation. Three gram-negative anaerobic periodontopathic organisms, Bacteroides gingivalis, Fusobacterium nucleatum, and Actinobacillus actinomycetemcomitans, bound in considerably higher numbers to the HR-9 matrix than did 6 strains of gram-positive facultative organisms typically associated with periodontal health. In a further experiment with B. gingivalis, the organism rapidly degraded Type IV collagen, the major macromolecular component constituting the HR-9 matrix. Streptococcus mitis, the nonperiodontopathic bacterium tested, did not degrade this model matrix. This study provides evidence that B. gingivalis, a periodontopathic bacterium, is able to adhere to and degrade basement membranes, whereas nonperiodontopathic organisms appear not to share in these abilities.

Attachment of oral bacteria to a basement-membrane-like matrix and to purified matrix proteins

The purpose of this study was to investigate the adherence of oral bacteria to an in vitro basement-membrane-like matrix and to selected individual macromolecular constituents of this matrix. Radiolabeled bacteria were incubated with basement-membrane-like matrices isolated from PF HR-9 cells. Bacteroides gingivalis 33277, Fusobacterium nucleatum FN-2, and Actinobacillus actinomycetemcomitans GA3(A) bound to the matrix in the range of 44 to 70%, considerably higher than the ranges of A. actinomycetemcomitans GA3(NA) and SUNY AB67 (range, 20 to 25%). The attachment of selected strains of gram-positive bacteria such as Streptococcus and Actinomyces spp. was much less frequent (range, 6 to 25%). Competitive inhibition studies demonstrated that preincubating the bacteria with fibronectin significantly decreased the binding of B. gingivalis by 51% but increased the binding of other gram-negative and gram-positive organisms tested. Similarly, preincubating the matrices with antifibronectin antibodies decreased the binding of B. gingivalis by 31%, whereas the other bacteria tested were either unaffected or binding was increased. The adherence of bacteria to purified basement membrane proteins was also investigated. Strain and species differences were seen in binding, but no clear relationship emerged between binding to an intact matrix and binding to isolated matrix proteins. The results of this study suggest that some gram-negative oral bacteria commonly associated with periodontal disease, such as B. gingivalis, A. actinomycetemcomitans, and F. nucleatum, bound in high numbers to basement-membrane-like matrices in vitro. On the other hand, the gram-positive strains tested bound in much fewer numbers. The results suggest that further studies with this in vitro model may aid in understanding the mechanisms by which oral bacteria adhere to basement membranes.

Previously unreported abnormalities of dermal basement membranes and collagen fibrils in a patient with X-linked spondyloepiphyseal dysplasia tarda

Electron microscopic findings of the skin biopsy of a boy with spondyloepiphyseal dysplasia tarda showed several novel features. The basement membrane of the epidermis showed focal irregular thickening and reduplication. The collagen fibres showed foci of fibrous long spacing collagen and marked variation in fibre diameter. Taken together these abnormalities have not been reported in any other condition.

The alteration in gingival basement membrane antigens in chronic periodontitis

The gingival basement membrane antigens, Type IV collagen, bullous pemphigoid antigen and epidermolysis bullosa acquisita antigen were studied by indirect immunofluorescence in 11 gingival specimens from patients with periodontitis and 2 normal gingival specimens. In the normal control gingival specimens, the antigens were all present and stained with a continuous linear pattern. In periodontitis, alterations occurred in the gingival basement membrane antigens in the apical portion of the pockets. These included thinning, interruptions, partial or complete absence involving one or more rete pegs and fragmentation. These alterations may result form the disease process or play a role in the pathogenesis.

Gingival wound healing in the presence of plaque-induced inflammation

An accelerated loss of connective tissue attachment has been reported following surgery in plaque-infected dentitions. It was the purpose of the present study to evaluate histologically the healing of incisional wounds in the gingival supracrestal region in the presence and absence of bacterially induced inflammation. In the experimental group, marginal periodontitis was induced around the teeth by tying plaque-retentive ligatures at the gingival margins and 10 weeks later an incisional wound was made from within the gingival sulcus to the crest of the bone. In the control group, similar incisional wounds were made in normal gingiva. In each group, three specimens were available for histologic and histometric analysis 1, 3, 7 and 21 days after wounding. In the control group, the wound healing sequence in the supracrestal region was similar to that reported following incisional cutaneous wounds. In the experimental group, epithelial continuity across the wound was re-established earlier, and marked invagination of epithelium occurred into the incision. This invagination was significantly greater than in control specimens at all time points. In addition, within the experimental group a second significant epithelial migration into the wound occurred between 7 and 21 days. The epithelial invagination extended through the major portion of the supracrestal area and terminated near the cementum surface. It is conceivable that marked epithelial invagination into a supracrestal wound may predispose to an accelerated loss of connective tissue attachment.

Ultrastructural and cytochemical observations on 5-fluorouracil-induced cleft-palate development in hamster

Sequential alterations in 5-fluorouracil-treated hamster fetal palate were studied by light and electron microscopy and by acid phosphatase cytochemistry. At an early stage in 5-fluorouracil-treated fetuses, when the palatal shelves were vertical, lysosomes first appeared in cells of the prospective fusion epithelium and then in the cells of subjacent mesenchyme. In contrast to controls, increasing numbers of both the epithelial and mesenchymal cells of the vertical palate showed lysosomal injury in 5-fluorouracil-treated fetuses as development progressed. Subsequently, the basal lamina in the vertical palate showed alterations, characterized initially by disturbances in lamina lucida, by fingerlike extensions of lamina densa, and ultimately by its complete breakdown. At a later stage, when shelves became horizontal, the lysosomes were absent in both the epithelial and mesenchymal cells, and the basal lamina continuity was restored. Unlike controls, however, 5-fluorouracil-treated horizontal shelves never contacted one another. Instead, the epithelia of the horizontal shelves underwent stratification. It appears that premature formation of lysosomes in palatal epithelial and mesenchymal cells following 5-fluorouracil treatment disrupts normal cytodifferentiation and affects the integrity of the basal lamina; both effects are associated with cleft-palate development.

Degradation of basement membrane collagen by proteinases from human gingiva, leukocytes and bacterial plaque

Basement membranes in human gingiva are found in dento-epithelial junction, epithelial-connective tissue junction and endothelium-connective-tissue junction where they have important attachment and filtering functions. The ability of plaque and gingiva-derived proteinases to degrade Type IV collagen, the major protein of basement membranes, was examined in vitro. The basement membrane collagen (Type IV) isolated from bovine lens capsules was incubated in the presence of enzyme samples. The degradation was assayed by the release of hydroxyproline from the insoluble substrate and by examining the peptide pattern of the residue by polyacrylamide gel electrophoresis. Salt extracts of inflamed gingival specimens degraded basement membrane collagen into soluble form and produced degradation products that were similar to those produced by human leukocyte extracts. Gingival crevicular fluid collected from patients with severe adult periodontitis also digested the substrate but the degradation pattern was different from the leukocyte and gingival extract samples. The pattern closely resembled the degradation produced by bacterial plaque extracts. A third type of cleavage was observed when collagenase from Clostridium histolyticum was incubated with basement membrane collagen. Crevicular fluid and the extracts from gingiva, leukocytes and plaque also contained gelatinase and elastase-like enzyme activities that have earlier been shown to be potent in degrading basement membrane. It was concluded that enzymes capable of degrading basement membrane collagen in gingivitis and periodontal disease may originate from both plaque bacteria and human leukocytes. It also appeared that the enzymes responsible are more likely to be gelatinase and elastase-like enzymes than specific collagenases.

Tissue culture of guinea-pig gall-bladder epithelium

Tissue culture of gall-bladder was attempted in the following media: Dulbecco, Eagle's minimum essential medium, NCTC 135, medium 199 and Ham's F12. Growth occurred in all of them for up to 2 weeks assessed by light microscopy. No enhancement of growth was induced by collagenase trypsin insulin or hydrocortisone. Scanning electron microscopy confirmed that new cells colonised the free surface of the explant. Transmission electron microscopy showed good preservation of the original tall epithelial cells for the period of study. The new migrating cells were flatter, but retained the morphological features of the columnar cells. Secretory granules were absent after 1 day in culture but increased amounts of glycogen and lipid began to appear in the epithelium.

A quantitative study of lamina densa alterations in hamster cheek pouch carcinogenesis

Lesions produced by topical application of 0.5 per cent. DMBA to the hamster cheek pouch epithelium were classified as hyperplasia, dysplasia and carcinoma groups using strict histological criteria. Untreated epithelium served as a control. Tissue samples from five animals in each group were processed for electron microscopy and electron micrographs from the epithelial-connective tissue junction were obtained from 5 blocks per animal. The micrographs were subjected to stereological intersection counting to determine the relative surface (SSLD, BM) of lamina densa which was in normal relationship to the basal cell plasma membranes. Quantitative results indicated a progressive loss of lamina densa during carcinogenesis and this was accompanied by the extrusion of pseudopodia from the basal cells through the gaps. The pseudopodia were frequently related to peripheral cytoplasmic microfilaments. Quantitative data confirmed the progressive nature of this loss, with values for SSLD,BM being of the order of 98 per cent., 88 per cent., 76 per cent, and 42 per cent. for normal epithelium and for the hyperplastic, dysplastic and carcinomatous lesions respectively. The loss of lamina densa is discussed in relation to the specificity of the response and to the development of features indicative of motility in transforming cells.

Current concepts of the dentogingival junction: the epithelial and connective tissue attachments to the tooth

This review leads to a concept in which the tissues of the dentogingival junction are dynamic rather that static. Even when they are pathologic, they can be reconstituted by repair. Both their cellular and extracellular components exhibit a high rate of turnover. Some of the cells are specialized for specific functions, such as attachment formation, and do not generate additional cells, but generative pools are always nearby. The cells are capable of movement and of positional change. The junctional epithelium can advance and retract. The cuticle width is alterable. The entire tissue is capable of regeneration after wounding. This dynamic group of tissues is well adapted for the healing of direct injuries produced during mastication. The tissues do remarkably well, over long periods, in their response to periodontal disease, whether due to direct bacterial or toxic damage, or to indirect damage via the migration of inflammatory cells into the lesion. The tissues show a capacity for repair and regeneration following the elimination of plaque formation and the resultant resolution of the inflammatory infiltrate. The complete story is not yet developed. The past 60 years are replete with fine contributions by distinguished workers. Additional contributions continue to be made. The inheritance from our predecessors has been used well and our expanded knowledge in this area now serves as the conceptual framework for further study.

Cholecystitis: a fine structural analysis

The epithelial cells from 40 gallbladders showing chronic cholecystitis and five with cholesterolosis were examined by electron microscopy. A number of features of non-specific cytological injury were noted some of which may have been related to the disease and others to anoxia. The basement membrane showed reduplication. Intraepithelial cells were identified as lymphocytes, polymorphonuclear leukocytes, macrophages and mast cells. Lipid droplets in the epithelial cells were found in 60 per cent. of the specimens.

Electron microscopic changes in human oesophageal epithelium in oesophagitis

At the ultrastructural level the inflamed oesophageal epithelium shows a variety of lesions. These include mitochondrial damage, intracellular oedema, membrane whorls and dilation of the endoplasmic reticulum and the appearance of keratohyaline and parakeratosis granules. The basement membrane shows changes ranging from thickening to areas of loss of continuity. There is an increase in the anchoring fibrils. The spaces between the cells are enlarged and contain varying amounts of debris rich in neutral mucosubstances. There are less membrane-coated granules in the inflamed epithelium than in the normal. The intra-epithelial intrusive cells demonstrated were lymphocytes and neutrophil polymorphs.

Ultrastructural studies of human gingiva. V. Microfibrils of elastic nature and their direct penetration of the basal lamina in chronic periodontitis

In this study, microfibrils widely distributed in the connective tissue of the gingival wall of periodontal pockets were examined by electron microscopy, Theirdistribution, ultrastructural characteristics, close association with fibroblasts and direct communication with the basal lamina were shown. The microfibrils in our specimens were observed in three different groupings (Types A, B, and C). They were believedto represent different stages of maturation of elastic fibera. There was a striking ultrastructural resemblance between oxytalan microfibrils, and the immature or imcompletetype of elastic fiber shown in this report.