Comparative effects of dimethylbenz(a)anthacene and a 15% olive-oil diet on cellular components and expression of apoptosis-related proteins in the spleen and mammary gland tumors of rats.

We compared effects of a high fat diet and a carcinogen on cellular elements of the spleen and mammary gland tumors in rats. Animals were fed a 15% olive-oil diet and a group of them were exposed to a carcinogen, dimethylbenz(a)anthacene (DMBA), in two doses of 10 mg/rat. Results of the experiments were evaluated after 4 months. We studied changes in the areas of different zones of the spleen related to production of B and T lymphocytes and also the number of cells in the spleen and tumors with positive reaction to receptors related to manifestation of apoptosis (FasL and p53) and receptors related to inhibition of apoptosis (bcl-2). In the spleen, dietary fats as well as DMBA alone decreased the zones related to production of B lymphocytes and increased the number of T lymphocytes. The combined effect of a carcinogen and a high fat diet manifested in an increase in the number of lymphoid cells and macrophages. In tumors from rats fed a low-fat diet, an extremely high number of lymphoid cells was seen in the border of tumors with T cell killers as a main component of these infiltrates. In tumors from rats fed a 15% olive-oil diet, the main component of the infiltrates were macrophages. High levels of p53+ and bcl-2+ cells were found in the spleen of rats exposed to a carcinogen. The combined effect of a carcinogen and the 15% olive-oil diet inhibited production of FasL and p53 receptors and stimulated synthesis of bcl-2 protein. In tumors, a carcinogen alone stimulated the high expression of FasL and p53 proteins, but in combination with the 15% olive-oil diet synthesis of these receptors decreased while production of bcl-2 protein increased sharply. This observation may serve as an additional proof of tumor-promoter effects of a high fat diet.

Effects of the soluble low-molecular-mass proteins on spleen activity and cellular composition of infiltrates in rat mammary gland tumors.

We showed previously that soluble low-molecular-mass tumor-associated antigens (TAA) could suppress chemically-induced tumorigenesis. In this study, we analyzed the mechanism of those findings. Studies were performed on the spleen and mammary gland tumors obtained from the following groups of rats: i) control rats treated with dimethyl-benz(alpha)antracene (DMBA), ii) vaccinated and carcinogen-treated rats with non regressed tumors, iii) vaccinated and carcinogen-treated rats with regressed tumors. Different zones of the spleen and tumors and their cellular content (Ki67+ and CD8+ cells, and macrophages) were analyzed morphometrically and immunohistochemically. Reaction of the spleen to vaccination was manifested in a significant increase in all areas of the white pulp and in a decrease in the size of the red pulp. The total number of cells in the white pulp (germinal center and PALS) and in the marginal zone was significantly higher in the spleen of rats with regressed tumors. The number of Ki67+ cells decreased significantly in both groups of vaccinated rats, but most prominently in the marginal zone and the red pulp in rats with regressed tumors. An increased number of CD8+ lymphocytes and macrophages was also seen in the red pulp. Different areas of the tumors (peripheral vs. inside at depth) showed different responses to vaccination and this difference was related to conditions of carcinogenesis, i.e. non-regressed vs. regressed tumors. In regressed tumors, all parameters studied were easily distinguishable in both areas of the tumors, while in non-regressed tumors, a marked distinction was seen only at their periphery. In regressed tumors, a negative correlation was seen at depth tumors between the number of Ki67+ cells and the number of CD8+ lymphocytes (r=-0.48). The findings indicated a strict antitumor effect of vaccination with the soluble low-molecular-mass TAA, which prevents the development of insufficiency of the immune system when an intensive immune reaction takes place.