In situ characterisation of the oral mucosal inflammatory cell response of rats induced by 4-nitroquinoline-N-oxide.

The inflammatory infiltrate induced in palatal and lingual mucosae of Sprague-Dawley rats after treatment with the water-soluble carcinogen 4-nitroquinoline-N-oxide (4NQO) was investigated using immunohistochemical methods on acetone-fixed frozen sections. Tissues from untreated and solvent-painted control rats were similar to each other and contained small numbers of OX-19+ T cells and larger numbers of W3/25+, LCA+, OX-19- cells within the lamina propria. This latter population could be divided into Ia+ and Ia- subpopulations. Although mucosal specimens from carcinogen-treated rats showed significantly increased numbers of T lymphocytes cells expressing the Ia+ and Ia-, W3/25+, LCA+, OX-19- antigenic phenotypes formed the two predominant cell populations beneath treated epithelium and surrounding tumour islands. Ia+ cells were often detected as focal collections adjacent to or within overlying epithelium which itself appeared to express Ia. None of the tumours showed this focal Ia+ cell infiltrate or expressed Ia. The infiltrates did not contain significant numbers of cytotoxic T cells (OX-8+ and OX-19+) or NK cells (OX-8+, OX-19[-], large granular lymphocytes) and, except for increased cell numbers, the populations present appeared similar to those found in normal mucosa. These results indicate that although immune reactions are stimulated by 4NQO treatment the effector cells necessary for controlling tumour development and growth are absent, perhaps reflecting a passive or stimulatory role in this experimental carcinogenesis model.