THE IMMUNE-RESPONSE OF RAT SPLEEN TO DIETARY-FIBERS AND TO LOW-DOSES OF CARCINOGEN - MORPHOMETRIC AND IMMUNOHISTOCHEMICAL STUDIES

The effects of high-fiber diets on anticancer immune response are ofte n masked by the effects of high-dose carcinogens. Using low levels of carcinogen the splenic immune response can be evaluated. Colon tumors were induced in rats with low doses of 1,2-dimethylhydrazine, in the f ollowing experimental groups: rats fed with low fiber diet without exp osure to carcinogen; rats exposed to the carcinogen and fed with low-f iber diet; rats exposed to carcinogen, and maintained on high-fiber di ets, and did not develop tumors; and rats that developed tumors after exposure to carcinogen and maintenance on either low-fiber or high-fib er diets. After 24 weeks their spleens were studied immunohistochemica lly and morphometrically. In tumor-free rats, low doses of carcinogen caused significant response of the lymphoid system. This was manifeste d in the intensive blast transformation and in an increase in the numb er of dendritic cells and macrophages in different structures of the s pleen. Dietary fibers activated these processes: the number of Ki-67 p ositive cells, macrophages and plasma cells increased significantly in the red pulp. A positive correlation was found between the effects of the carcinogen and proliferation of lymphocytes in the white pulp, an d to lesser degree between high-fiber diets and lymphocytic abundance in the red pulp. The number of splenic apoptotic lymphocytes decreased in rats exposed to carcinogen. In tumor-bearing rats, immune insuffic iency of the splenic responses was seen in the significant decrease of the areas of the mantle layer and the periarterial sheaths, as result of the decreased number of lymphocytes. Dietary fibers reduced the de gree of this insufficiency. Even low doses of carcinogen cause a signi ficant splenic immune response. This reaction has a compensatory chara cter with macrophages, B and T cells participating. Addition of any hi gh-fiber diet after the exposure to carcinogen activated the lymphocyt e proliferation in the spleen.