Immunohistochemical characterization of cellular infiltrates in epidermal tumors induced by two-stage and complete chemical carcinogenesis in mouse skin.

We investigated the population and pattern of the infiltrated cells in both benign and malignant epidermal tumors which were induced chemically with benzo(a)pyrene (B(a)P) in murine skin. In benign papillomas, which were evolved by a two stage carcinogenesis regimen, a slight to mild inflammatory infiltration around the tumors was observed, and cells infiltrating into the tumor nests were rarely seen. In carcinomas, which were produced by a complete carcinogenesis regimen, a dense inflammatory infiltration was observed around the tumor nests. The infiltrated cells were characterized as T-lymphocytes, macrophages, and neutrophils. Natural killer (NK) cells were found around and in the tumor nests, but their number was small. Both T-lymphocytes and macrophages were found to invade the tumor nests in squamous cell carcinoma whose duration was more than four weeks. This experimental carcinogenesis animal model allows the detailed quantitative and functional analysis of the infiltration of immunocompetent cells into epidermal tumors.