Characterization of epimyoepithelial islands in benign lymphoepithelial lesions of major salivary gland: an immunohistochemical and ultrastructural study

Digital image analysis of intraepithelial B-lymphocytes to assess lymphoepithelial lesions in salivary glands of Sjögren's syndrome patients

OBJECTIVE

Salivary glands of primary SS (pSS) patients characteristically harbour periductal infiltrates, in which lymphoepithelial lesions (LELs) can develop. LELs are composed of hyperplastic ductal epithelium with infiltrating lymphocytes and may assist in the challenging diagnostic process of pSS. As manual identification of LELs remains difficult, we aimed to identify LELs by using an objective digital image analysis (DIA) algorithm that detects intraepithelial lymphocytes.

METHODS

A virtual triple-staining technique developed for this study was used to count intraepithelial lymphocytes in consecutive slides stained for CD3 (T-lymphocytes), high-molecular-weight cytokeratin (hmwCK) (striated ducts) and CD20 (B-lymphocytes) in labial and parotid gland biopsies in a diagnostic cohort of 109 sicca patients. Patients were classified as having pSS or non-SS according to the ACR-EULAR classification criteria.

RESULTS

T-lymphocytes were detected in almost all analysed ducts of pSS and non-SS sicca patients, whereas intraepithelial B-lymphocytes were present in 59-68% of labial and parotid gland biopsies of pSS patients, against only 2-3% of patients classified as non-SS. Intraepithelial B-lymphocytes were found in almost all striated ducts with hyperplasia (LELs). Remarkably, ∼25% of analysed striated ducts without hyperplasia of pSS patients also contained B-lymphocytes (precursor-LELs). Furthermore, presence of intraepithelial B-lymphocytes was associated with clinical parameters of pSS (i.e. serology).

CONCLUSION

The presence of intraepithelial B-lymphocytes in salivary gland biopsies of sicca patients is a clear indicator of pSS and can be used as an objective alternative to LEL scoring. Therefore, identification of B-lymphocyte-containing ducts should be added to the diagnostic histopathological work-up of patients suspected of pSS.

Defining the role of myoepithelium in salivary gland neoplasia

Neoplastic myoepithelium is considered to be the key cellular participant in morphogenetic processes responsible for the variable histologic appearances of many salivary gland tumors. Nevertheless, controversy still exists concerning its participation in some types of salivary gland neoplasms. This has been largely due to the difficulty in fully characterizing the wide spectrum of morphologic and immunophenotypic expressions of neoplastic myoepithelium compared with the normal counterpart. However, in recent years, our understanding regarding the phenotypic, immunophenotypic, ultrastructural, and biochemical properties of myoepithelium has advanced. Here we discuss the role of neoplastic myoepithelium in the scope of salivary gland neoplasia and present this information from a practical diagnostic standpoint.

Benign lymphoepithelial lesion of the parotid gland with sebaceous differentiation

The salivary duct system in the setting of chronic sialadenitis is predisposed to undergo a variety of cellular modifications. This report documents a rare type of metaplasia of a parotid benign lymphoepithelial lesion. Epimyoepithelial islands showing focal sebaceous differentiation and pure sebaceous cell nests in addition to their usual histologic appearance were noted throughout the lesion. The possible pathogenesis is discussed through a review of the literature.

Ultrastructure and three-dimensional imaging of epimyoepithelial islands in benign lymphoepithelial lesions

Benign lymphoepithelial lesions of the salivary glands associated with Sjögren's syndrome are characterized by extensive infiltration of lymphoid cells, atrophy of acini and the presence of so-called epimyoepithelial islands. This report describes ultrastructural and three-dimensional reconstructive studies of epimyoepithelial islands performed at Tokyo Women's Medical College. Ultrastructural examination showed that these islands are composed mainly of epithelial cells containing intermediate filaments and/or tonofilament bundles, scattered lymphocytes and plasma cells. Myoepithelium-like cells containing myofilaments were sometimes found in the peripheral portion of the myoepithelial islands. Also, mitotic figures were rarely found in these islands. Three-dimensional reconstructive study revealed that the epimyoepithelial islands are not isolated cell clusters but are continuous hypertrophic duct-like structures. These results suggest that the epimyoepithelial islands are derived from proliferating duct epithelial cells, especially those of large peripheral ducts.

Pathology of the salivary glands: the contribution of electron microscopy

Electron microscopy has a limited role in the diagnosis of primary salivary gland tumors, although it can be helpful in metastatic lesions of possible salivary gland origin. The diversity of subtypes in salivary gland tumors, as well as the range of histomorphology within any one subtype, is unparalleled in any other human tumor. This and their relative infrequency causes diagnostic problems for pathologists. Ultrastructural techniques have been of major importance in determining the inter-relationship of these tumors for classification purposes, revealing the subtle variations in common cellular differentiation pathways, determining the organization of tumor cells, and displaying the importance of extracellular matrix materials in establishing diagnostic criteria for each of the many subtypes. Electron microscopy has also been valuable in non-neoplastic salivary gland disease and has an increasing role in experimental studies involving tissue from human and animal salivary parenchyma.

The pathobiology of salivary gland. I. Growth and development of rat submandibular gland organoids cultured in a collagen gel matrix

Fragments of rat submandibular gland (organoids) which maintained the topological organization of the parent tissue were cultured in a three-dimensional collagen gel matrix for up to 30 days. At 48 h, vigorous peripheral outgrowth had occurred around each organoid. This was accompanied by central necrosis and the bridging of adjacent organoids. By day 5, large cyst-like spaces occupied the centre of many organoids. Bromodeoxyuridine labelling indicated that a considerable proportion of the lining cells were proliferating. Organoid growth peaked at between 5 and 10 days. Thereafter, the number of viable colonies and proliferating cells declined. Addition of isoproterenol after 24 h culture resulted in marked morphological alterations, with earlier and more prolific outgrowth and a greater tendency for organoids to flatten and grow out over the surface of the gel with squamous differentiation. Ultrastructurally, nuclear and cytoplasmic features of isoproterenol-treated and untreated cultures were similar. The secretory granules and extensive rough endoplasmic reticulum of terminal tubule cells, evident in organoids immediately after isolation, were infrequent after 24 h and absent by 48 h. Similar alterations occurred in the few acinar cells, so by 5 days the cultures were composed entirely of a uniform population of primitive, dedifferentiated cells. Further uses of this culture systems will include the study of diseases and disorders of the salivary glands as well as normal growth and differentiation pathways.

A review of the proliferative capacity of major salivary glands and the relationship to current concepts of neoplasia in salivary glands

The classification of salivary gland tumors relies heavily on histogenetic postulates. One of these, the semipluripotential reserve cell theory, suggests that certain reserve cells in specific segments of the duct system of major and minor salivary glands are critical to the development of neoplasms in these glands. However, direct evidence in support of this hypothesis is unavailable. This survey of proliferative capacity in normal salivary gland is based on a review of data in the literature, our observations of DNA synthetic and mitotic activity in developing rat and human salivary gland, and autoradiographic studies of induced cell proliferation in rat salivary gland. Autoradiography of neonatal rat salivary gland after tritiated thymidine administration, and electron microscopy of these tissues, reveals that as well as duct basal cells, luminal cells at all levels of the duct system and even acinar cells are capable of DNA synthesis and mitosis. Indeed, in such studies, more luminal than basal cells are seen in mitosis. In adult rat salivary gland induced to undergo hyperplasia, more acinar cells than intercalated duct cells are in the S phase of the cell cycle. However, cycling cells were observed even in striated ducts and, importantly, both basal and luminal cells of major interlobular excretory ducts are also labeled. Similar findings are present in fetal and adult human salivary glands. From such observations, it is evident that dividing cells are not limited to basal cells of excretory ducts and luminal cells of intercalated ducts, so that there is no support for the semipluripotential bicellular reserve cell hypothesis. However, there is considerable evidence for a multicellular theory of tumor histogenesis; that is, any of the multiplicity of cell types in normal salivary gland have the potential to give use to any of the various types of tumor occurring in this organ.

Myoepithelioma--new concepts of histology and classification: a light and electron microscopic study

Based on histological, immunohistochemical, and ultrastructural studies, it is now apparent that the modified myoepithelial cell component of pleomorphic adenomas has a considerable range of cytological features. We reasoned that myoepitheliomas could be tumors with a similar spectrum of neoplastic myoepithelium but lacking the ductal element displayed in pleomorphic adenomas. A review of available salivary gland tumors identified 40 examples based on this definition. Architecturally, these myoepitheliomas displayed either nonmyxoid (solid), myxoid (pleomorphic adenoma-like), reticular (canalicularlike), or mixed growth patterns, while cytologically the lesions were composed of spindle-type (32.5%), hyaline-type (7.5%), epithelial-type (45.0%), clear-type (2.5%), or mixed-type (12.5%) tumor cells. Electron microscopy was carried out on eight examples and detailed immunohistochemistry on two methanol-fixed cases. As a result of the current review of myoepitheliomas and the description of similar lesions in the literature, it is our contention that salivary gland myoepitheliomas are not as rare as has been purported.

Characterization of cytoskeletal proteins in basal cells of human parotid salivary gland ducts

From previous immunofluorescent, immunohistochemical and ultrastructural studies, myoepithelial cells have been reported to be absent from the striated and excretory ducts of human salivary gland. Yet recently, certain anti-cytokeratin monoclonal antibodies which specifically label the myoepithelium of salivary gland acini and intercalated ducts have also been found to stain basally situated cells in both striated and excretory ducts. In this study, we have used eight samples of normal human parotid gland (methacarn-fixed and frozen sections) to establish if basal cells of striated and excretory ducts have the cytoskeletal protein complement (actin and cytokeratins) of myoepithelial cells. Using a muscle-specific actin, HHF35, not only is the myoepithelium of acini and intercalated ducts stained in all cases, but stellate and spindle shaped cells are also detected all along the inter- and intralobular striated ducts in four of the eight examples. With double-labeled frozen sections and fluorescent microscopy, the actin-specific probe, phalloidin, and the myoepithelial-selective anti-cytokeratin 14 antibody, 312C8-1, confirm that the striated duct does have a population of basal cells with the cytoskeletal protein make-up of myoepithelium. The monoclonal antibody 8.12 (specific for cytokeratin 13 and 16) also stains some basal cells of striated and excretory ducts, as well as luminal cells of ducts at all levels, but does not label the myoepithelium of acini and intercalated ducts. Both the anti-cytokeratin antibodies and the actin-detecting mechanisms reveal that the basal cell population of striated and excretory ducts is more heterogeneous, and likely functionally more complex, than has been realized previously. Such findings are not in agreement with certain aspects of current theories of the histogenesis of salivary gland tumours.