The ultrastructure of initial changes in hapten-exposed rat oral mucosa

The endothelium in early experimental contact hypersensitivity of the oral mucosa. Leukocyte-binding properties and ultrastructure

Contact hypersensitivity is characterized by an early and specific diapedesis of mononuclear cells into the site of antigenic challenge. In order to study the functional and ultrastructural properties of the endothelium involved in the recruitment of leukocytes, Sprague-Dawley rats were skin sensitized to DNFB; and this was followed by challenge of the oral mucosa. In vitro binding of peripheral blood mononuclear cells to high endothelial venules in lymph nodes was highly specific but no affinity of peripheral blood mononuclear cells to the vessels was observed in normal oral mucosa or in early contact hypersensitivity. However, 10 days after repeated DNFB challenge, occasional vessels bound overlaid peripheral blood mononuclear cells. Ultrastructurally, we identified migration of mononuclear cells through small venules three h after challenge. The vessels involved, however, did not display morphological signs of activation reminiscent of high endothelial venules in lymph nodes. Mast cell degranulation was evident as early as 30 min after challenge, and a possible mechanism for mast cell-mediated leukocyte recruitment is discussed.

Ultrastructural examination of experimentally induced premalignant lesions

Lesions induced in hamster cheek pouch using dimethylbenz(alpha)anthracene were studied by transmission electron microscopy and compared with normal tissue. Features regarded as suggestive of progression towards malignancy were: increased numbers of membrane-bound vesicles in basal cells, gaps in the lamina densa associated with widening of the lamina lucida and an irregular epithelial-connective tissue junction, the presence of cerebriform cells and frequent close association of 2 or more intra-epithelial cells (lymphocytes, cerebriform cells, Langerhans cells).

Irritant and sensitizing potential of copper, mercury and tin salts in experimental contact stomatitis of rat oral mucosa

HgCl2, CuSO4, SnCl2, SnCl4 or sodium lauryl sulphate (SLS) were openly applied to rat oral mucosa for 1 min, followed 6 h later by histologic examination of the tissue response. Granulocytes were the predominant inflammatory cells and no lymphocytic infiltration could be seen with any of the substances tested. Irritant threshold levels were defined histologically for each of the substances. CuSO4 was found to be non-irritant at all concentrations. The addition of non-irritant concentrations of SLS lowered the threshold levels for HgCl2 and SnCl2, but CuSO4/SLS was non-irritant at all concentrations tested. Preapplication to the mucosa of SLS at non-irritant concentrations gave results with HgCl2, SnCl2 and CuSO4 similar to those with SLS added to the metal salt solutions. Lesions of allergic contact type could not be induced in the oral mucosa to any of the metal salt preparations.

Chemically induced inflammation in rat oral mucosa

The toxic, irritative, and sensitizing effects of topically applied sodium lauryl sulfate (SLS), dithranol triacetate (DTA), nonanoic acid in methyl- or propyl ester (NAM, NAP) in the buccal mucosa were investigated in a Sprague-Dawley rat model. Semi-quantitative evaluations of cellular infiltrates were performed in routine histologic preparations. The toxic potential was tested with 2% and 0.2% solutions. All substances, except 0.2% SLS, caused an increased cellularity, mainly of a mononuclear cell type. The low dose of NAM induced stronger inflammatory reactions than the high dose. Repeated applications of 2% solutions decreased the response compared to one application, except for NAM, where a clear irritative potential was observed. Pre-exposure of dorsal skin prior to buccal painting resulted in an enhanced reaction to NAM and NAP, whereas no sensitizing capacity was noted in SLS or DTA in this model.

Immunogenic potential of some mercury compounds in experimental contact allergy of the rat oral mucosa

The contact allergenic potential of substances included in a "dental screening test" has been investigated in a previously established animal model for producing contact allergy. We were unable to produce contact hypersensitivity with any of the original formulas. HgCl2 was selected for further studies and, in order to improve its penetration, butanol was used as a solvent. Sensitization was, however, not obtained with any of the HgCl2/butanol formulas. Our results are discussed in relation to the requirements of reaching immunogenic threshold levels of mercury in the tissue.

New views on the construction of human gingival epithelium

The effects on the basal and spinous layers of human keratinized oral epithelium of 2 glutaraldehyde-based fixatives with buffers hypoosmolar and isoosmolar to blood, respectively, have been investigated. The first-mentioned solution produced an electron microscopic image corresponding to the classical view, that is an epithelium consisting of closely-packed cells having short and stubby membrane projections and separated by an extremely narrow intercellular space. In the Langerhans cells, the specific granules appeared racket-shaped and had a unilaminar limiting membrane with a periodic structure along its internal face. There are strong reasons to believe that these morphological characteristics are swelling artifacts. The last-mentioned fixative produced keratinocytes provided with numerous microvilli and membrane ruffles and disk-shaped Langerhans cell granules surrounded by a trilaminar membrane. Concomitantly, the intercellular space appears very wide and there is evidence for the view that this is a more realistic picture of the in vivo situation and not a gross distortion caused by shrinking during the tissue processing. Broad interstices can explain certain basic events as rapid cell motility within the epithelium and offer efficient pathways for rapid transport of substances.