Morphological and morphometric studies of the splenic antitumor immune response, elicited by liposome-covered soluble p53 kDa antigen, in chemically-induced rat colon cancer.

We evaluated the splenic morphometric changes in rats treated with carcinogen to study development of anti-cancer immune response. When liposome-covered soluble 53 kDa antigen (s53) was injected into these rats, significant tumor-suppression was seen and the percentage of tumor-free animals rose from 15.4% in non-vaccinated rats to 53.8%. In the spleens of carcinogen treated rats that did not develop tumors, activity of B lymphocytes increased significantly. This was manifested by the expansion of the germinal centers to 50.9% of the follicular area reflecting depletion of B cells, and the decrease of the mantle layer to 48.9% of the follicles. A similar picture was seen with T lymphocytes: the area of the marginal zone decreased to 55.2% of the T zone of the white pulp, and that of the periarterial lymph sheaths (PALS) to 33.6%. In tumor-bearing rats features of the immune decompensation were seen: the germinal centers increased to 96.5% of the follicular area, and the mantle layer and PALS decreased significantly. Vaccination prevented these effects, especially in tumor-bearing rats: the PALS occupies 30.4% of the white pulp and the marginal zone 56.1%, and the mantle layer occupied 58.1% of the follicular zone. Similar changes were found in vaccinated rats without tumors reflecting the compensatory character of the immune reaction in vaccinated rats. In conclusion, we found that treatment with carcinogen followed by vaccination with the s53-liposomes complex stimulated the activity of the splenic B, and to a lesser degree the T systems.