Two-colour immunofluorescence marker study of pleomorphic adenomas

Functional Histology of Salivary Gland Pleomorphic Adenoma: An Appraisal

The complex microstructure of salivary gland pleomorphic adenoma is examined in relation to function. Events related to secretion of macromolecules and absorption, responses to the altered microenvironment and controversies concerning epithelial-mesenchymal transition versus modified myoepithelial differentiation are explored. Their effects on tumor cell phenotypes and arrangements are emphasized. Heterotopic differentiation and attempts at organogenesis are also considered. The approach allows interpreting microstructure independently of histogenetic perceptions, envisaging the tumor cells as a continuum, endorsing luminal structures as the principal components, and defining pleomorphic adenoma as a benign epithelial tumour characterized by variable epithelial-mesenchymal transition, secretion/differentiation and metaplasia.

Thomsen-Friedenreich (T) antigen as marker of myoepithelial and basal cells in the parotid gland, pleomorphic adenomas and adenoid cystic carcinomas. An immunohistological comparison between T and sialosyl-T antigens, alpha-smooth muscle actin and cytokeratin 14

Controversy centres on the role and identification of myoepithelial (MEC) and basal cells in salivary gland tumours, and recent studies suggest that both basal cells and myoepithelial cells participate in the formation of salivary gland tumours. We have correlated the expression of different well-known markers of normal MEC/basal cells (i.e. alpha-smooth muscle actin and cytokeratin 14) with T (Thomsen-Friedenreich) antigen and its sialylated derivative: sialosyl-T antigen,) in 17 normal parotid glands and in two tumour types with MEC participation (i.e pleomorphic adenomas (PA) and adenoid cystic carcinomas (ACC)) using immunohistology with well-defined monoclonal antibodies (MAbs). Paraffin-embedded/fresh frozen tissue sections were studied from 33/17 patients with PA and 15/7 patients with ACC. In normal parotid tissue coexpression of alpha-smooth muscle actin, cytokeratin 14, T and sialosyl-T antigens was found in all MEC and in some of the basal cells lining striated ducts. The remaining basal cells exclusively expressed cytokeratin 14, T and sialosyl-T antigens. In the tumours, cells believed to be modified myoepithelial cells showed two different staining patterns: 1) Coexpression of alpha-smooth muscle actin, cytokeratin 14, T and sialosyl-T antigens, and 2) Coexpression of cytokeratin 14, T and sialosyl-T antigens, but no alpha-smooth muscle actin. The epithelial ductular structures in the tumours showed aberrant expression of cytokeratin 14, T and sialosyl-T antigens, and cytokeratin 14 was the only marker of cells in solid undifferentiated areas of adenoid cystic carcinomas. Our study supports the view, that modified "myoepithelial" cells in the tumours consist of a mixture of basal cells and myoepithelial cells. None of the investigated structures was in itself an ideal marker in the identification of MEC/basal cells. The cells can be identified by a combination of markers (i.e. cytokeratin 14, alpha-smooth-muscle actin, T and sialosyl-T antigens).

Characterization of a novel cell line from pleomorphic adenoma of the parotid gland with myoepithelial phenotype and producing interleukin-6 as an autocrine growth factor

A cell line was obtained from a primary culture of a pleomorphic adenoma of the parotid gland in a 24-year-old woman. The cells of the line (PA 16/23) grew spontaneously in minimal culture conditions and showed stable morphologic characteristics over 30 passages. PA 16/23 cells had immunophenotypic and ultrastructural features similar to those of transformed myoepithelial cells, which are regarded as the precursors of pleomorphic adenomas. Furthermore, these cells have been demonstrated immunocytochemically to contain interleukin-6 (IL-6) on light and electron microscopic examination. IL-6 also has been found by enzyme-linked immunosorbent assay in the culture supernatant and has been proven to be capable of stimulating growth of the PA 16/23 cells.

Expression of HLA class I and II (DR, DP and DQ) determinants in fetal and postnatal salivary glands

Fetal (n = 20) and postnatal (n = 40) parotid glands were examined by two-colour immunohistochemistry combining monoclonal and polyclonal antibody reagents to study the expression of HLA class I and II (DR, DP, and DQ), CD45 and CD3. The epithelium lacked class II during fetal life, whereas class I determinants appeared in some acini and most major ducts. Fetal vessels were positive for both class I and class II (mainly DR), suggesting constitutive expression. Some class II-positive (DR greater than DP greater than DQ) histiocytic cells, scattered CD45+ leucocytes, and very few CD3+ T cells were present in the fetal stroma. The epithelium remained DR-negative the first few weeks after birth, but brisk expression was seen subsequently. DP and DQ remained virtually negative in the epithelium throughout the first year. A slight postnatal increase of class II expression (DR greater than DP greater than DQ), along with an apparent decrease in class I, was observed in the endothelium. The number of class II-positive histiocytic cells, CD45+ leucocytes and CD3+ T cells, as well as the proportion of presumably activated (DR+) T cells, increased a few weeks after birth. The local immune system hence seemed to be stimulated by extrinsic factors, but the overall number of T cells nevertheless remained small. Stimuli other than T cell-derived lymphokines, therefore, probably explained the brisk postnatal epithelial DR induction.

Abundant dendritic cells express HLA-DR in pleomorphic adenomas

Most pleomorphic adenomas were found to contain abundant dendritic cells (DC) with major histocompatibility complex (MHC) class II (HLA-DR) expression. Their immunohistochemical staining features were suggestive of dendritic histiocytic cells. Extensive phenotypic characterization by two-colour immunofluorescence staining for various cell markers was performed. The DC expressed both HLA class I and II determinants, vimentin, S-100 protein, and various monocyte-related markers (10G11, 3D10, 7G5 or CD11a, 8C2) but were negative for leucocyte common antigen (CD45), Leu-6 (CD1), and the myelomonocytic L1 antigen. Characterization of HLA-DR positive DC isolated by an immunomagnetic bead method confirmed the immunohistochemical staining pattern that corresponds to the phenotype of interdigitating cells. Morphological and immunological implications of the abundant presence of these cells in pleomorphic adenomas are discussed.