Epithelial dendritic cells and connective tissue macrophages in oral carcinogenesis and the effects of systemic Corynebacterium parvum

Epithelial dendritic cells (EDC) and connective tissue macrophages were examined during the induction and growth of oral squamous cell carcinomas in Sprague-Dawley rats treated with the carcinogen 4-nitroquinoline N-oxide (4NQO) and the immune potentiator Corynebacterium parvum. Splenomegaly was induced in all animals receiving C. parvum. Acetone-fixed frozen sections of the palate and tongue were stained using an indirect immunoperoxidase technique and monoclonal antibodies to rat Ia (MRC OX-6) and macrophage subpopulations (ED1, ED2, ED3). EDC were predominantly Ia+, ED1-, ED2- and ED3-. The lamina propria contained Ia+, ED1+ and ED2+ cells; ED3-reactive cells were rare. ED2+ cells predominated in the interstitial connective tissue of deeper muscle. In the non-invasive tissues, the number of positive cells (Ia+EDC and connective tissue Ia+, ED1+ and ED3+ cells) increased significantly throughout the experimental period (0-9 months), were significantly more prevalent in the test tissues (4NQO, 4NQO + C.parvum, C.parvum) compared to untreated controls and, at 9 months, the carcinogen-treated rats (4NQO, 4NQO + C.parvum) had significantly more Ia+ EDC and connective tissue Ia+ cells than C.parvum controls. Irrespective of the marker under study, there were no significant differences between rats treated with 4NQO or 4NQO + C.parvum at any time during the experimental period. Similarly, intra-epithelial Ia+ and ED1+ cells increased significantly throughout the experimental period in all test groups compared to untreated controls, but no significant differences were evident between carcinogen-treated animals (4NQO, 4NQO + C.parvum) and C.parvum controls. Significant positive correlations between connective tissue Ia+ and ED1+ cells and also intra-epithelial Ia+ and ED1+ cells were present in all experimental groups; connective tissue ED2+ and ED3+ cell numbers did not correlate with any of the other phenotypes and intra-epithelial ED2+ and ED3+ cells were rare/absent. Palatal and/or lingual tumours developed in 80% of carcinogen-treated rats by 9 months and the tumour incidence was similar in rats treated with either 4NQO or 4NQO + C.parvum. There were no significant differences in the number of Ia+ EDC between the infiltrating and the non-invasive overlying epithelium of the lingual carcinomas and the non-invasive lingual epithelium treated with either 4NQO or 4NQO + C.parvum.(ABSTRACT TRUNCATED AT 400 WORDS)